HAWKINS ELECTRICAL GUIDE
NUMBER EIGHT

Fig. 2,583.—General Electric simultaneous record of three waves with common zero.

Fig. 2,584.—General Electric simultaneous record of three waves with separate zeros.

Figs. 2,585 and 2,586.—Oscillograms (from paper by Morris and Catterson-Smith, Proc. I. E. E., Vol. XXXIII, page 1,023), showing how the current varies in one of the armature coils of a direct current motor. Fig. 2,585 was obtained with the brushes in the neutral position, and fig. 2,586 with the brushes shifted forward.

Fig. 2,587.—Oscillogram by Bailey and Cleghorne (Proc. I.E.E., Vol. XXXVIII), showing the sparking pressure or pressure between the brush and the commutator segment at the moment of separation. The waves fall into groups of three owing to the fact that there were three armature coils in each slot.

Fig. 2,588.—Various wave forms. The sine wave represents a current or pressure which varies according to the sine law. A distorted wave is due to the properties of the circuit, for instance, the effect of hysteresis in an iron core introduced into a coil is to distort the current wave by adding harmonics so that the ascending and descending portions may not be symmetrical. A peaked wave has a large maximum as compared with its virtual value. A peaked wave is produced by a machine with concentrated winding.

Fig. 2,589.—Diagram illustrating Joubert's step by step method of wave form measurement.

Fig. 2,590.—Four part commutator method of wave form measurement. The contact device consists of two slip rings and a four part commutator. One slip ring is connected to one terminal of the source, the other to the voltmeter, and the commutator to the condenser. By adjusting R when a known direct current pressure is impressed across the terminals, the voltmeter can be rendered direct reading.

Fig. 2,591.—Modified four part commutator method of wave form measurement (Duncan's modification). By this method one contact maker can be used for any number of waves having the same frequency. Electro-dynamometers are used and the connections are made as here shown. The moving coils are connected in series to the contact maker, and the fixed coils are connected to the various sources to be investigated, then the deflection will be steady and by calibration with direct current can be made to read directly in volts.

Fig. 2,592.—Diagram illustrating the ballistic galvanometer method of wave form measurement. The test may be made as described in the accompanying text, or in case the contact breaker is belted instead of attached rigidly to the shaft, it could be arranged to run slightly out of synchronism, then by taking readings at regular intervals, points will be obtained along the curve without moving the contact breaker. If this method be used, a non-adjustable contact breaker suffices. In arranging the belt drive so as to run slightly out of synchronism, if the pulleys be of the same size, the desired result is obtained by pasting a thin strip of paper around the face of one of the pulleys thus altering the velocity ratio of the drive slightly from unity.

Figs.. 2,593 and 2,594.—Two curves representing pressure and current respectively of a rotary converter. Fig. 2,593, pressure wave V, fig. 2,594 current wave C. These waves were obtained from a converter which was being driven by an alternator by means of an independent motor. The rotary converter was supplying idle current to some unloaded transformers and the ripples clearly visible in the pressure wave V, correspond to the number of teeth in the armature of the rotary converter.

Fig. 2,595.—Diagram illustrating zero method of wave measurement with contact maker. The voltage of the battery must be at least as great as the maximum pressure to be measured and must be kept constant.

Fig. 2,596.—Diagram illustrating zero method of wave measurement with contact breaker. The voltage of the battery must be at least as great as the maximum pressure to be measured and must be kept constant.

Fig. 2,597.—Diagram of Hospitalier ondograph showing mechanism and connections. It represents a development of Joubert's step by step method of wave form measurement.

Fig. 2,598.—View of Hospitalier ondograph. In operation, a long pivoted pointer carrying a pen and actuated by electro-magnets, records on a revolving drum a wave form representing the alternating current, pressure or current wave.

Fig. 2,599.—General Electric moving coil oscillograph complete with tracing table. The tracing table is employed for observing the waves, and by using a piece of transparent paper, the waves under observation appear as a continuous band of light which can be traced, thus making a permanent record. This is not, however, to be regarded as a recording attachment, and can not be used where instantaneous phenomena are being investigated. The synchronous motor for operating the synchronous mirror in connection with tracing and viewing attachment is wound for 100 to 115 volts, 25 to 125 cycles, and should, of course, be run from the same machine which furnishes power to the circuit under observation. A rheostat for steadying and adjusting the current should be connected in series with the motor. The beam from the vibrator mirrors striking this synchronous mirror moves back and forth over the curved glass, and gives the length of the wave; the movement of the vibrator mirror gives the amplitude, and the combination gives the wave complete. An arc lamp or projection lantern produces the image reflected by the mirrors upon the film, tracing table or screen. For the rotation of the photographic film, a small direct current shunt wound motor is ordinarily used.

Fig. 2,600.—General Electric moving coil oscillograph. The moving elements consist of single loops of flat wire carrying a small mirror and held in tension by small spiral springs. The current passing down one side and up the other, forces one side forward and the other backward, thus causing the mirror to vibrate on a vertical axis. The vibrator elements fit into chambers between the poles of electro-magnets, and are adjustable, so as to move the beam from the mirror, both vertically and horizontally. A sensitized photographic film is wrapped around a drum and held by spring clamps. The drum, with film, is placed in a case and a cap then placed over the end, making the case light, when the index is either up or down. The loading is done in a dark room. A driving dog is screwed into the drum shaft, and which, when the drum and case are in place, revolves the film past a slot. When an exposure is to be made, the index is moved from the closed position, thus opening the slot in the case and exposing the film to the beam of light from the vibrating mirrors when the electrically operated shutter is open. The slot is then closed by moving the index to "Exposed." A slide with ground glass can be inserted in place of the film case or roll holder to arrange the optical system when making adjustments. The shutter operating mechanism is arranged so as to hold the shutter open during exactly one revolution of the film drum. There are two devices connected to the shutter operating mechanism; one opens the shutter at the instant the end of the film passes the slot; the other opens immediately, at any part of the film, and both give exposure during one revolution. The first is useful when making investigations in which the events are either recurring, or their beginnings known or under control, and the second when the time of the event is not under control, such as the blowing of fuses or opening of circuit breakers.

Fig. 2,601.—General Electric moving coil oscillograph with case removed, showing interior construction and arrangement of parts. The oscillograph is furnished complete with a three element electro-magnet galvanometer, optical system, shutter and shutter operating mechanism, film driving motor and cone pulleys, photographic and tracing attachments, 6 film holders, and the following repair parts, for vibrators: 6 extra suspension strips; 6 vibrator mirrors; 1 box gold leaf fuses; 1 bottle mirror cement; 1 bottle damping liquid.

Fig. 2,602.—Oscillogram showing the direct current pressure of a 25 cycle rotary converter (below), and (above) the pressure wave taken between one collector ring and one commutator brush. The 12 ripples per cycles in the direct current voltage are due to a 13th harmonic in the alternating current supply.

Fig. 2,603.—Curves by Morris, illustrating the dangerous rush of current which may occur when switching on a transformer. The circuit was broken at F and made again at G. The current was so great as to carry the spot of light right off the photographic plate due to the fact that a residual field was left in the core after switching off, and on closing the switch again the direction of the current was such as to tend to build up the full flux in the same direction as this residual flux. The dotted lines have been drawn in to show how the actual waves were distorted from the normal.

Fig. 2,604.—Siemens-Blondel moving coil type oscillograph. The coil is in the shape of a loop of thin wire, which is suspended in the field of an electro-magnet excited by continuous current. The current to be investigated is sent through this loop, which in consequence of the interaction of current and magnetic field, begins to vibrate. The oscillations are rendered visible by directing a beam of light from a continuous current arc lamp onto a small mirror fixed to the loop. The light reflected by the mirror is in the form of a light strip, but by suitable means this is drawn out in respect of time, so that a curve truly representing the current is obtained. The loop of fine wire is stretched between two supports and is kept in tension by a spring. As the spring tension is considerable, the directive force of the vibrating system is large, and its natural periodicity very high. The mirror is fixed in the center of the loop, and has an area of 1 square mm. In order to protect the loops from mechanical injury they are built into special frames. The mirrors are of various sizes, the loop for demonstration purposes (projection device) being provided with the largest mirror and the most sensitive loop with a mirror of the smallest dimensions.

Figs. 2,605 and 2,606.—Oscillograms reproduced from a paper by M. B. Field on "A Study of the Phenomena of Resonance by the Aid of Oscillograms" (Journal of E. E., Vol. XXXII). The effect of resonance on the wave forms of alternators has been the subject of much investigation and discussion; it is a matter of vital importance to the engineer in charge of a large alternating current power distribution system. Fig. 2,605 shows the pressure curve of an alternator running on a length of unloaded cable, the 11th harmonic being very prominent. Fig. 2,606 shows the striking alteration produced by reducing the length of cable in the circuit and thus causing resonance with the 13th harmonic.

Fig. 2,607.—General view of electro-magnet form of Duddell moving coil oscillograph, showing oil bath and electro-magnet. This instrument is specially designed to have a very high natural period of vibration (about 1/10,000 of a second) so as to be suitable for accurate research work. It is quite accurate for frequencies up to 300 per second. In the figure, A is the brass oil bath in which two vibrators are fixed; B, core of electro-magnet which is excited by two coils, one of which, C, is seen. The ends of these two coils are brought out to four terminals at D, so that the coils may be connected in series for 200 volt, or in parallel for 100 volt circuits. The bolts, E,E, hold the oil bath in position between the poles of the magnet. F,F,F (one not seen), are levelling screws; G,G, terminals of one vibrator; H, fuse; K, thermometer with bulb in center of oil bath.

Figs. 2,608 to 2,612.—Vibrator of Duddell moving coil oscillograph and section through oil bath of electro-magnet oscillograph. The vibrator consists of a brass frame W, which supports two soft iron pole pieces P,P. Between these, a long narrow groove is divided into two parts by a thin soft iron partition, which runs up the center. The current being led in by the brass wire U, passes from an insulated brass plate to the strip, which is led over an ivory guide block, down one of the narrow grooves and over another guide block, the loops round the ivory pulley O, which puts tension on the strip by the spring N, back to the guide block again, up the other narrow groove, and out by way of the insulated brass plate and lead U. Halfway up the grooves the center iron partition R is partially cut away to permit of a small mirror M, bridging across from one strip to the other, being stuck to the strips by a dot of shellac at each corner. The figure illustrates one type of vibrator in which P is removable from W for ease in repairing. In type 1, these pole pieces P,P are not removable. The vibrators are placed side by side in the gap between the poles S,S of the electro-magnet, see fig. 2,610. Each vibrator is pivoted about vertical centers, the bottom center fitting in the base of the oil bath, and the one at the top being formed by a screw in the cock piece Y. It can thus be easily turned in azimuth, its position being fixed by the adjusting screw L, a spiral spring serving to keep the vibrator always in contact with this screw. Since each cock piece can be independently moved forward or backward, each vibrator can be tipped slightly in either of these directions so that complete control over the mirrors is obtained and reflected spots of light may be made to coincide with that reflected from the fixed zero mirror, which latter is fixed to a brass tongue in between the two vibrators. A plano-convex lens of 50 cm. focal length is fixed on the oil bath in front of the vibrator mirrors to converge the reflected beams of light. It will be noticed that this lens is slightly inclined so that no trouble will be given by reflections from its own surface. The normal distance from the vibrator mirrors to the scale of photographic plate is 50 cm., and at this distance, a convenient working deflection on each side of the zero line is 3 to 4 cm. This is obtained with a R.M.S. current through the strips of from .05 to .1 of an ampere according to wave form, etc. The maximum deflection on each side of the zero line should not exceed 5 cm. while the maximum R.M.S. current through the strips should in no case exceed .1 ampere.

Fig. 2,613.—Duddell moving coil oscillograph with projection and tracing desk outfit. The outfit is designed for teaching and lecture purposes. In operation, after the beam of light from the arc lamp has been reflected from the oscillograph mirrors, it falls on a vibrating mirror which gives it a deflection proportional to time in a direction at right angles to the deflection it already has and which is proportional to the current passing through the oscillograph. It is therefore only necessary to place a screen in the path of the reflected beam of light to obtain a trace of the wave form. Since the vibrating mirror is vibrated by means of a cam on the shaft of a synchronous motor, which motor is driven from, or synchronously with, the source of supply whose wave form is being investigated, the wave form is repeated time after time in the same place on the screen, and owing to the "persistence" of vision, the whole wave appears stationary on the screen. The synchronous motor with its vibrating mirror, mentioned above, is located underneath the "tracing desk." When used in this position a wave a few centimeters in amplitude is seen through a sheet of tracing paper which is bent round a curved sheet of glass. A permanent record of the wave form can thus easily be traced on the paper. A dark box which is designed to hold a sheet of sensitized paper in place of the tracing paper, can be fitted in place of the tracing desk. Thus an actual photographic record of the wave form is obtained. If the synchronous motor be transferred from its position underneath the tracing desk to the space reserved for it close to the oscillograph, the beam of light is then received on a large mirror which is placed at an angle of about 45 degrees to the horizontal and so projects the wave form onto a large vertical screen which should be fixed about two and a half meters distant. Under these conditions a wave form of amplitude 50 cm. each side the zero line may be obtained which is therefore visible to a large audience.

Figs. 2,614 and 2,615.—Sectional view of permanent magnet form of Duddell moving coil oscillograph. This instrument has a lower natural period of vibration (1/3000 second) than the type shown in fig. 2,612, and therefore is not capable of accurately following wave forms of such high frequency, but it is sufficiently quick acting to follow wave forms of all ordinary frequencies with perfect accuracy. It is easier to repair, and more portable owing to the fact that the magnetic field is produced by a permanent magnet instead of an electro-magnet. This also renders the instrument suitable for use on high tension circuits without earth connection, as, owing to the fact that no direct current excitation is required, the instrument is more easily insulated than other types.

Fig. 2,616.—Diagram of connections of Duddell oscillograph to high pressure circuit. The modification necessary for high pressure circuit only applies to the vibrator which gives the pressure wave and consists in adding two more resistances, R₄ and R₅. Referring to fig. 2,617, it will be seen that in case fuse f₂ blows, or the vibrator be accidentally broken, the full supply voltage is immediately thrown on the instrument itself. This is not permissible in high voltage work and therefore the resistance R₅ is introduced as a permanent shunt to the oscillograph vibrator. The resistance R₄ is an exact duplicate of R₂ being a 21 ohm plug resistance box for adjusting the sensitivity of the vibrator to an even figure. In practice R₅ is usually a part of R₁, and in most of the high voltage resistances, two taps are brought out near one end to serve as R₅. One of these taps is usually 50 ohms distant from the end terminal and the other only 5 ohms from the end. The use of these taps is as follows: The large resistance consisting of R₁ + R₅ is so chosen with respect to the voltage of the circuit under investigation that the current through R₁ is about .1 ampere. It should never be more than this continuously. Then R₄ is connected to the 50 ohm tap, and since the resistance of the oscillograph vibrator circuit is variable from about 5 to 26 ohms by means of R₄, the current can be controlled through the oscillograph from about .066 to .091 of an ampere, enabling an open wave form to a convenient scale to be obtained. If it now be desired to record large rises of pressure, such as may occur in cases of resonance, the height of the wave must be reduced in order to keep these rises on the plate. This is accomplished by disconnecting R₄ from the 50 ohm tap and connecting it to the 5 ohm tap, when the current through the vibrator will be from .05 to .016 of an ampere according to whether the resistance R₄ is in or out of circuit. When, instead of using the falling plate, the cinematograph camera is being used, it becomes necessary always to work on the 5 ohm tap since the width of the film is much less than that of the plate, and the current must therefore be less. In experiments where sudden rises of voltage are expected it is often advisable to keep R₁ as great as possible. That end of the resistance R₁ referred to as R₅ in the diagram should be securely connected to the supply main and no switch or fuse used. A switch may, if desired, be used in series with R₁, provided it be inserted at the point where R₁ joins the supply main remote from R₅. It will be seen that fuses f₁ and f₂ are shown. Provided that the connections are always made in accordance with the diagram, and the vibrators are always shunted by R₅ or R₃ respectively, there is not much objection to the use of these fuses, but on general principles it is wise to avoid fuses in high tension work and accordingly with each permanent magnet oscillograph, dummy fuses are supplied, which can be inserted in place of the ordinary fuses when desired. The remark previously made about keeping both vibrators and the frame of the instrument at approximately the same pressure applies with additional emphasis in high pressure work.

Fig. 2,617.—Diagram of connections of Duddell oscillograph to low pressure circuit, R₁ is a high non-inductive resistance connected across the mains in series with one of the vibrators. S₂ is a switch, and f₂, the fuse (on the oscillograph in this circuit). The resistance of R₁ in ohms should be rather more than ten times the voltage of the circuit, so that a current of a little less than .1 of an ampere will pass through it. The vibrator will then give the curve of the circuit on an open scale. (For the projection oscillograph, the resistance R₁ should be only twice the supply voltage, since .5 of an ampere is required to give full scale deflection on a large screen.) To obtain the current wave form, the shunt R₃ is connected in series with the circuit under investigation and the second vibrator is connected across this shunt. Here also f₁ is a fuse, S₁ a switch, and R₂ an adjustable resistance box. The switch S₁ is however unnecessary if the plug resistance box supplied for R₂ be used, since an infinity plug is included in this box. The shunt R₃ should have a drop of about 1 volt across it in order to give a suitable working current through the vibrator. The resistance R₂ is not absolutely essential, but it is a great convenience in adjusting the current through the vibrator. It is a plug resistance box, the smallest coil being .04 of an ohm and the total 21 ohms. Being designed to carry .5 ampere continuously it can be used with any other type of Duddell oscillograph, and by its use the sensitiveness of the vibrator can be adjusted so that a round number of amperes in the shunt gives 1 mm. deflection. This adjustment is best made with direct current. It should be noted in connecting the oscillograph in circuit, that the two vibrators should be so connected to the circuit that it is impossible that a higher pressure difference than 50 volts should exist between one vibrator and the other, or between either vibrator and the frame. To ensure attention to this important point, a brass strap is provided which connects the two vibrators together and to the frame of the instrument. This does not mean that this point must necessarily be earthed since the frame of the instrument is insulated from the earth. It is advisable, however, to earth it when possible.

Figs. 2,618 and 2,619.—Two curves obtained with the falling plate camera and illustrating the discharge of a condenser through an inductive circuit. When taking curve A the resistance in the circuit was very small compared to the inductance, while before taking curve B an additional non-inductive resistance was inserted in the circuit so that the oscillations were damped out much more rapidly although the periodic time remained approximately constant.

Fig. 2,620.—Synchronous motor with vibrating mirror as used with Duddell moving coil oscillograph. Since the motor must run synchronously with the wave form it is required to investigate, it should be supplied with current from the same source. The motor can be used over a wide range of frequencies (from 20 to 120). When working at frequencies below 40, it is advisable to increase the moment of inertia of the armature, and for this purpose a suitable brass disc is used. The armature carries a sector, which cuts off the light from the arc lamp during a fraction of each revolution, and a cam which rocks the vibrating mirror. It makes one revolution during two complete periods, and the cam and sector are so arranged that during 1½ periods, the mirror is turning with uniform angular velocity, while during the remaining half period, the mirror is brought back quickly to its angular position, the light being cut off by the sector during this half period.

Figs. 2,621 to 2,623.—Interior of cinematograph camera as used on Duddell moving coil oscillograph for obtaining long records. The loose side of case is shown removed and one of the reels which carry the film lying in front. The spool of film which is placed on the loose reel A, passes over the guide pulley B, then vertically downward between the brass gate D (shown open in the figure), and the brass plate C. The exposure aperture is in the plate C and can be opened or closed by a shutter controlled by the lever M. The groove in the plate C, and the springs which press the gate D flat on the plate C, prevent the film having any but a vertical motion as it passes the exposure slit. E is the sprocket driving pulley which engages with the perforations on the film and unwinds it from the reel A to reel H. Outside the case on the far side of it is secured to the axle G a three speed cone pulley. This is driven by a motor of about 1/7 horse power, which also drives, through the gears shown, the sprocket pulley E. Close to the grooved cone pulley is a lever carrying a jockey pulley L, and a brake, which latter is normally held onto the cone pulley by a spring and so causes the loose belt to slip. By pressing a lever which is attached to the falling plate camera case, the brake can be suddenly released and at the same time the jockey pulley caused to tighten the belt onto the grooved cone pulley, so that the starting and stopping of the film is controlled independently of the driving motor, and being quickly accomplished avoids waste of film. Both reels are alike and each is made in two pieces. The upper reel is loose on its axle and its motion is retarded slightly by a friction brake. The lower reel is also loose on its axle, but it is driven by means of a friction clutch, the clutch always rotating faster than the reel so that the used film delivered by the sprocket pulley E is wound up as fast as delivered. K is the front face of one reel, the boss on it pushes into the tube on the other half H, which serves not only to unite the two halves, but also to secure the end of the film which is doubled through J.

Fig. 2,624.—Portion of oscillograph record taken with cinematograph film camera, showing the rush of current and sudden rise of voltage at the moment of switching on a high pressure feeder.

Fig. 2,625.—Portion of oscillograph record taken with a cinematograph film camera showing the effect of switching off a high pressure feeder and illustrating the violent fluctuations produced by sparking at the switch contacts.

Fig. 2,626.—Curves reproduced from an article by J. T. Morris in the Electrician. "On recording transitory phenomena by the oscillograph."

Fig. 2,627.—First rush of current from an alternator when short circuited, showing unsymmetrical initial wave of current, becoming symmetrical after a few cycles. 25 cycles.

Fig. 2,628.—Pressure wave obtained from narrow exploring coil on alternator armature, indicating distribution of field flux. The terminal voltage of the alternator is very nearly a sine wave, 60 cycles; about 17 volts.

Fig. 2,629.—The waves of voltage and current of an alternating arc. A, voltage wave; B, current wave showing low power factor of the arc without apparent phase displacement. 60 cycles.

Fig. 2,630.—Rupturing 650 volt circuit. A, current wave; B, 25 cycle wave to mark time scale.

Fig. 2,631.—First rush of current from alternator when short circuited, showing unsymmetrical current wave, also wave of field current caused by short circuit current in armature. Upper curve, armature current; lower curve, field current.

Fig. 2,632.—Mazda (tungsten) lamp, showing rapid decrease to normal current as filament heats up. 25 cycles.

Fig. 2,633.—Current wave in telephone line corresponding to sustained vowel sound "i," as in machine; voice pitched at A 110.

Fig. 2,634.—Carbon lamp, showing rapid increase to normal current as filament heats up. 25 cycles.

Fig. 2,635.—Short circuit current on direct current end of rotary converter, 21,500 amperes maximum. Upper curve, direct current voltage; lower curve, direct current amperage. Duration of short circuit about .1 second.

Figs. 2,645 and 2,646.—Diagrams illustrating general principles of switchboard connections.

Fig. 2,646.—Fort Wayne switchboard panel for one alternator and one transfer circuit. Diagram giving dimensions, arrangement of instruments of board, and method of wiring. The different forms of standard alternating current switchboard panels for single phase circuits made by the Fort Wayne Electric Works are designed to fulfill all the usual requirements of switchboards for this class of work. The line includes panels equipped for a single generator; for one generator and two circuits; one generator and one transfer circuit; one generator, an incandescent and an arc lighting circuit; and also feeder panels of different kinds.

Fig. 2,647.—General Electric small plant alternating current switchboard, designed for use in small central stations and isolated plants. They are for use with one set of bus bars, to which all generators and feeders are connected by means of single throw lever switches or circuit breakers, suitable provision being made for the parallel operation of the generators.

Fig. 2,648.—Crouse-Hinds voltmeter and ground detector radial switch, arranged for mounting on the switchboard. The switch proper is placed on the rear of the board with hand wheel, dial, and indicator only on the front side. The current carrying parts are of hard brass, with contact surfaces machined after assembling. The contact parts are of the plunger spring type, and the cross bar has fuse connections. Ground detector circuits are marked G+ and G- for two wire system, and G+, G-, GN+ and GN- for three wire system. When the voltmeter switch is to be used as a ground detector, two circuits are required for a two wire system, and four circuits for a three wire system, that is, a six circuit voltmeter and ground detector switch for use on a two wire system has two circuits for ground detector and four circuits for voltmeter readings. A six circuit voltmeter and ground detector switch, for use on a three wire system, has four circuits for ground detector and two circuits for voltmeter readings.

Figs. 2,649 and 2,650,—Wiring diagrams of Crouse-Hinds voltmeter and ground detector switches. Fig. 2,649 voltmeter switch; fig. 2,650 voltmeter and ground detector switch. A view of the switch is shown in fig. 2,648; it is designed for use on two or three wire systems up to 300 volts.

Figs. 2,651 to 2,653.—Diagrams of connections for generator panels. Key to symbols: A, ammeter; A.S., ammeter switch; C.T., current transformer; F., fuse; F.A., direct current field ammeter; F.S., field switch; G.C.S., governor control switch; L.S., limit switch (included with governor motor); O.S., oil switch; P.I.W., polyphase indicating wattmeter; P.W.M., polyphase watthour meter; P.R., pressure receptacle; P.P., pressure plug; Rheo., rheostat; S., shunt; S.R., synchronizing receptacle; S.P., synchronizing plugs; T.B., terminal board for instrument leads; V, alternating current voltmeter.

Figs. 2,654 and 2,655.—Diagrams illustrating a simple method of determining bus capacity as suggested by the General Electric Co. Fig. 2,654 relates to any panel; the method is as follows: 1. Make a rough plan of the entire board, regardless of the number of panels to be ordered. The order of panels shown is recommended, it being most economical of copper and best adapted to future extensions. 2. To avoid confusion keep on one side of board everything pertaining to exciter buses, and on other side everything pertaining to A. C. buses. 3. With single lines represent the exciter and A. C. buses across such panels as they actually extend and by means of arrows indicate that portion of each bus which is connected to feeders and that portion which is connected to generators. Remember that "Generator" and "Feeder" arrows must always point toward each other, otherwise the rules given below do not hold. Note also that the field circuits of alternator panels are treated as D. C. feeders for the exciter bus. 4. On each panel mark its ampere rating, that is, the maximum current it supplies to or takes from the bus. For A. C. alternator panels the D. C. rating is the excitation of the machines. 5. Apply the following rules consecutively, and note their application in fig. 2,654. (For the sake of clearness ampere ratings are shown in light face type and bus capacities in large type.) A. Always begin with the tail of the arrow and treat "generator" and "feeder" sections of the bus separately. B. Bus capacity for first panel = ampere rating of panel. C. Bus capacity for each succeeding panel = ampere rating of panel plus bus capacity for preceding panel. (See sums marked above the buses in fig. 2,654.) D. For a panel not connected to a bus extending across it, use the smaller value of the bus capacities already obtained for the two adjoining panels. (See exciter bus for panel C.) E. The bus capacity for any feeder panel need not exceed the maximum for the generator panels (see A. C. bus for panel G) and vice versa (see exciter bus for panel B). Hence the corrections made in values obtained by applying rules B and C. The arrangement of panels shown in fig. 2,654 is the one which is mostly used. The above method may, however, be applied to other arrangements, one of which is shown in fig. 2,655. Here the generators must feed both ways to the feeders at either end of the board so that in determining A. C. bus capacities it is necessary to first consider the generators with the feeders at one end, and then with the feeders at the other end as shown by the dotted A. C. buses. The required bus capacities are then obtained by taking the maximum values for the two cases.

Fig. 2,656.—End view showing general arrangement of switchboards for 240, 480, and 600 volt alternating current. The cut shows a single throw oil switch mounted on the panel.

Figs. 2,657 and 2,658.—Two views of a feeder panel, showing general arrangement of the devices assembled thereon. A, circuit breaker; B, ammeter; C, voltmeter; D, switches.

Figs. 2,659 to 2,666.—Diagram of connections for three phase feeder panels. Key to symbols: A, ammeter; A.S., three way ammeter switch; B.A.S., bell alarm switch; C.T., current transformer; F, fuse; O.S., oil switch; P.I.W., polyphase indicating wattmeter; P.W.M., polyphase watthour meter; T.B., terminal board; T.C., trip coils for oil switch.

Figs. 2,667 and 2,668.—Diagrams of connections for two phase and three phase installations: A and A1, ammeter; C.C., constant current transformer; C.T., current transformer; D.R., discharge resistance; F, fuse; F.S., field switch; L.A., lightning arrester; O.S., oil switch; P.P., pressure plug; P.R., pressure receptacle; P.T., pressure transformer; S and S1, plug switches; T.C., oil switch trip coil; V, voltmeter.

Fig. 2,669.—Crouse-Hinds radial ammeter switch, arranged for mounting directly on the switchboard. It is designed for use with external shunt ammeters of any make or capacity, and in connection with the required number of shunts, makes possible the taking of current readings of a corresponding number of circuits by means of one ammeter. The wiring diagram is shown in fig. 2,670.

Fig. 2,670.—Wiring diagram for Crouse-Hinds radial ammeter switch as illustrated in fig. 2,669. The switch proper is on the rear of the switchboard, and the hand wheel dial and indicator on the front.

Figs. 2,671 to 2,676.—The effect of self-induction. In a non-inductive circuit, as in fig. 2,672, the whole of the virtual pressure is available to cause current to flow through the lamp filament, hence it will glow with maximum brilliancy. If an inductive coil be inserted in the circuit as in fig. 2,674, the reverse pressure due to self-induction will oppose the virtual pressure, hence the effective pressure (which is the difference between the virtual and reverse pressures), will be reduced and the current flow through the lamp diminished, thus reducing the brilliancy of the illumination. The effect may be intensified to such degree by interposing an iron core in the coil as in fig. 2,676, as to extinguish the lamp.

Fig. 2,677.—Measurement of self induction when the frequency is known. The apparatus required consists of a high resistance or electrostatic a.c. voltmeter, d.c. ammeter, and a non-inductive resistance. Connect the inductive resistance to be measured as shown, and close switch M, short circuiting the ammeter. Connect alternator in circuit and measure drop across R and across X_i. Disconnect alternator and connect battery in circuit, then open switch M and vary the continuous current until the drop across R is the same as with the alternating current, both measurements being made with the same voltmeter; read ammeter, and measure drop across X_i. Call the drop across X_i with alternating current E, and with direct current E_i, and the reading of the ammeter J. Then L = √E² + E_i² ÷ 2π f I. If the resistance X_i be known, and the ammeter be suitable for use with alternating current, the switch and R may be dispensed with.

 Then L = √E² - X_i² I_i² ÷ 2π f I, where I_i is the value of the alternating current. The resistance of the voltmeter should be high enough to render its current negligible as compared with that through X_i.

Fig. 2,678.—Transposition diagram for two parallel lines consisting of two wires each.

Fig. 2,679.—Transposition diagram for three phase, three wire line, transposing at the vertices of an equilateral triangle. The line is originally balanced and becomes unbalanced on transposing, a procedure which should be resorted to only to prevent mutual induction.

Fig. 2,680.—Transposition diagram of three phase, three wire line, with center arranged in a straight line.

Fig. 2,681.—Capacity effect in single phase transmission line. The effect is the same as would be produced by shunting across the line at each point an infinitesimal condenser having a capacity equal to that of an infinitesimal length of circuit. For the purpose of calculating the charging current, a very simple and sufficiently accurate method is to determine the current taken by a condenser having a capacity equal to that of the entire line when charged to the pressure on the line at the generating end. The effect of capacity of the line is to reduce the pressure drop, that is, improve the regulation, and to decrease or increase the power loss depending on the load and power factor of the receiver.

Fig. 2,682.—Capacity effect in a three phase transmission line. It is the same as would be produced by shunting the line at each point by three infinitesimal condensers connected in star with the neutral point grounded, the capacity of each condenser being twice that of a condenser of infinitesimal length formed by any two of the wires. The effect of capacity on the regulation and efficiency of the line can be determined with sufficient accuracy in most cases by considering the line shunted at each end by three condensers connected in star, the capacity of each condenser being equal to that formed by any two wires of the line. An approximate value for the charging current per wire is the current required to charge a condenser, equal in capacity to that of any two of the wires, to the pressure at the generating end of the line between any one wire and the neutral point.

Figs. 2,683 to 2,687.—Skin effect and shield effect. Fig. 2,683, section of conductor illustrating skin effect or tendency of the alternating current to distribute itself unequally through the cross section of a conductor as shown by the varied shading, which represents the current flowing most strongly in the outer portions of the conductor. For this reason it has been proposed to use hollow or flat instead of solid round conductors; however, with frequency not exceeding 100, the skin effect is negligibly small in copper conductors of the sizes usually employed. In figs. 2,684 and 2,685, or 2,686 and 2,687, if two adjacent conductors be carrying current in the same direction, concentration will occur on those parts of the two conductors remote from one another, and the nearer parts will have less current, that is to say, they will be shielded. In this case, the induction due to one conductor will exert its opposing effect to the greatest extent on those parts of the other conductor nearest to it; this effect decreasing the deeper the latter is penetrated. After crossing the current axis, the induction will still decrease in magnitude, but will now aid the current in the conductor. Hence, the effect of these two conductors on one another will make the current density more uniform than is the case where the two conductors adjacent to one another are carrying current in opposite directions, as in figs. 2,685 and 2,686, therefore, the resistance and the heating for a given current will be smaller. If the two return conductors be situated on the line passing through the center of the conductors just considered, the effect will be to still further concentrate the current; the distribution symmetry will be further disturbed, and the resistance of the conductor system increased. It is therefore difficult to say which of the two cases considered holds the advantage so far as increasing the resistance is concerned. The case, however, in which the phases are mixed has much the smaller reactive drop.

Fig. 2,688.—Electromagnetic and electrostatic fields surrounding the conductors of a transmission line. The electromagnetic field is represented by lines of magnetic force that surround the conductors in circles, (the solid lines), and the electrostatic field by (dotted) circles passing from conductor to conductor across at right angles to the magnetic circles. For any given size of wire and distance apart of wires there is a certain voltage at which the critical density or critical gradient is reached, where the air breaks down and luminosity begins—the critical voltage where corona manifests itself. At still higher voltages corona spreads to further distances from the conductor and a greater volume of air becomes luminous. Incidentally, it produces noise. Now to produce light requires power and to produce noise requires power. Air is broken down and is heated in breaking down, and to heat also requires power; therefore, as soon as corona forms, power is consumed or dissipated in its formation. When this phenomenon occurs on the conductors of an alternating current circuit a change takes place in relation to current and voltage. On the wires of an alternating current transmission line, at a voltage below that where corona forms—at a voltage where wires are not luminous—considerable current, more or less depending on voltage and length of wire, flows into the circuit as capacity current or charging current.

Figs. 2,689 to 2,692.—Triangles for obtaining graphically, impedance, impressed pressure, etc., in alternating current circuits. For a full explanation of this method the reader is referred to Guide 5, Chapter XLVII on Alternating Current Diagrams. A thorough study of this chapter is recommended.

Fig. 2,693.—Mechanical analogy of power factor, as exemplified by a locomotive "poling" a car off a siding. The car and locomotive are shown moving in parallel directions, and the pole AB, inclined at an angle ϕ. Now, if the length of AB be taken to represent the pressure exerted on the pole by the locomotive, then the imaginary lines AC and BC, drawn respectively parallel and at right angles to the direction of motion will represent respectively the useful and no energy (wattless) components; that is to say, if the pressure AB be applied to the car at an angle ϕ, only part of it, AC, is useful in propelling the car, the other component, BC, being wasted in tending to push the car off the track at right angles to the rails, being resisted by the flanges of the outer wheels.

Fig. 2,694.—Diagram showing that the apparent current is more than the active current, the excess depending upon the angle of phase difference.

Fig. 2,695.—Diagram showing components of impedance volts. Compare this diagram with figs. 2,689 and 2,671, and note that the term "reactance" is the difference between the inductance drop and the capacity drop if the circuit contain capacity, for instance, if inductance drop be 10 volts and capacity drop be 7 volts then reactance 10-7 = 3 volts.

Figs. 2,696 to 2,698.—Example of wiring showing where inductance is negligible, and where it must be considered in wire calculations.

Figs. 2,699 to 2,703.—Stranded copper cables. For conductors of large areas and in the smaller sizes where extra flexibility is required it becomes necessary to employ stranded cables made by grouping a number of wires together in either concentric or rope form. The concentric cable as here illustrated is formed by grouping six wires around a central wire thereby forming a seven wire cable. The next step is the application in a reverse direction of another layer of 12 wires and a nineteen wire cable is produced. This is again increased by a third layer of eighteen wires for a 37 wire cable and a fourth layer of 24 wires for a 61 wire cable. Successive layers, each containing 6 more wires than that preceding, may be applied until the desired capacity is obtained. The cuts show sectional views of concentric cables each formed from No. 10 B. & S. gauge wires.

Fig. 2,704.—Rope type of stranded copper cable which is used when a high degree of flexibility is required. The construction of this cable is the stranding together of seven groups, each containing seven wires and producing a total of 49 wires. In cases when a greater carrying capacity is desired than can be obtained through the use of the 7 × 7 or 49 wire cable, the number of groups is increased to nineteen thereby making a total of 133 wires (19 × 7).

Fig. 2,705.—Elevation of small station with direct drive, showing arrangement of the boiler and engine, piping, etc.

Fig. 2,706.—Diagram illustrating graphical method of determining the center of gravity of a system in locating the central station.

Fig. 2,707.—Exterior of central station at Lewis, Ia.; example of very small station located in the principal business section of a town. It also illustrates the use of a direct connected gasoline electric set. The central station is located on Main Street, which is the principal thoroughfare, and is installed in a low one story building for which a mere nominal rental charge is paid, the company having the option to buy the property later at the value of the land plus the cost of the improvements and simple interest on the same. To the front of an old frame building about 16 feet by 28 feet has been built a neat, well lighted concrete block room, about 16 feet by 16 feet, carrying the building to the lot line and affording ample space for the generating set and switchboards, and such desk room as is needed for the ordinary office business of the company. In this room, which is finished in natural pine with plastered walls, has been installed a standard General Electric 25 kw. gasoline electric generating set consisting of a four cylinder, four cycle, vertical water cooled, 43-54 H.P. gasoline engine, direct connected to a three phase, 2,300 volt, 600 R.P.M. alternator with a 125 volt exciter mounted on the same shaft and in the same frame. With the generating set is a slate switchboard panel equipped with three ammeters, one voltmeter, an instrument plug switch for voltage indication, one single pole carbon break switch, one automatic oil circuit breaker line switch and rheostats. Instrument transformers are mounted above and back of the board. For street lighting service a 4 kw. constant current transformer has been installed, and with it a gray marble switchboard panel mounted on iron frames and carrying an ammeter and a four point plug switch. On a board near the generator set are mounted in convenient reach suitable wrenches, spanners, and repair parts and tools. To cool the engine cylinders five 6 × 8 steel tanks have been installed in the old building, a pump on engine giving forced circulation.

Fig. 2,708.—Map of Cia Docas de Santos hydro-electric system; an example of station location remote from the center of distribution. In the figure A is the intake; B, flume; C, forebay; D, penstocks; E, power house; F, narrow gauge railway; G, general store; H, point of debarkation; I, transmission line; J, dead ends; K, sub-station. Santos, in the republic of Brazil, is one of the great coffee shipping ports of the world, and for the development of its water front has required an elaborate system of quays. These have been developed by the Santos Dock Company, which holds a concession for the whole water front. The company, needing electric power for its own use, has developed a system deriving its power from a point about thirty miles from the city, where a small stream plunges down the sea coast from the mountain range that runs along it. The engineers have estimated that 100,000 horse power can be obtained from this source.

Fig. 2,709.—Station location. The figure shows two distribution centers as a town A and suburb B supplied with electricity from one station. For minimum cost of copper the location of the station would be at G, the center of gravity. However, it is very rarely that this is the best location. For instance at C, land is cheaper than at G, and there is room for future extension to the station, as shown by the dotted lines, whereas at G, only enough land is available for present requirements. Moreover C is near the railroad where coal may be obtained without the expense of cartage, and being located at the river, the plant may be run condensing thus effecting considerable economy. The conditions may sometimes be such that any one of the advantages to be secured by locating the station at C may more than offset the additional cost of copper.

Fig. 2,710.—Section of the central station or "electricity works" at Derby, showing boiler and engine room and arrangement of bunkers, conveyor, ash pit, grates, boilers (drum, heating surface and superheater), economizer, flue, turbines, condenser pumps, etc.; also location of switchboard gallery and system of piping.

Fig. 2,711.—View of old and new Waterside stations. The new station at the right has an all turbine equipment of ten units, some Curtis and some Parsons machines, two have a capacity of 14,000 kw., and the remaining eight are of 12,000 kw. each. The old Riverside station, seen at the left is described on page 1940.

Fig. 2,712.—View illustrating the location of a station as governed by the presence of a water falls. In such cases the natural water power may be at a considerable distance from the center of gravity of the distribution system because of the saving in generation. In the case of long distance transmission very high pressure may be used and a transformer step down sub-station be located at or near the center of gravity of the system, thus considerably reducing the cost of copper for the transmission line.

Fig. 2,713.—View of a station admirably located with respect to transportation of the coal supply. As shown, the coal may be obtained either by boat or rail, and with modern machinery for conveying the coal to the interior of the station, the transportation cost is reduced to a minimum.

Fig. 2,714.—Floor plan of part of the turbine central station erected by the Boston Edison Co., showing two 5,000 kw. Curtis steam turbines in place. The complete installation contains twelve 5,000 kw. Curtis steam turbines, a sectional elevation being shown in fig. 2,758, page 1,971.

Fig. 2,715.—Example of central station located remote from the distributing center and furnishing alternating current at high pressure to a sub-station where the current is passed through step down transformers and supplied at moderate pressure to the distribution system. In some cases the sub-station contains also converters supplying direct current for battery charging, electro-plating, etc.

Fig. 2,716.—Diagram illustrating diversity factor. By definition diversity factor = combined actual maximum demand of a group of customers divided by the sum of their individual maximum demands. Example, a customer has fifty (50) watt lamps and, of course, the sum of the individual maximum demands of the lamps is 2.5 kw. watts ("connected load"). The customer's maximum demand, however, is 1.5 kw. Hence, the diversity factor[A] of the customer's group of lamps is 1.5 ÷ 2.5 = .6. In the diagram the ordinates of the curves show the ratio maximum demand to connected load for various kinds of electric lighting service in Chicago.

Fig. 2,717.—Load curve for one day.

Fig. 2,718.—Load curve for one year.

Fig. 2,719.—Load curve of plant supplying power for the operation of motors in a manufacturing district. The horizontal dotted lines show suitable power ratings. A properly designed steam plant has a large overload capacity, a hydraulic plant has a small overload capacity, and a gasoline engine plant has no overload capacity. Accordingly, the peak of the load (maximum load) may be 25 or 30 per cent. in excess of the rated capacity of a steam plant, not more than 5 or 10 per cent. in excess of the rated capacity of a hydraulic plant, not at all in excess of the rated capacity of a gas engine plant.

Fig. 2,720.—Floor plan of an electrical station having a belted drive with counter shaft.

Fig. 2,721.—Elevation of station having a belted drive with countershaft, as shown in plan in fig. 2,720.

Fig. 2,722.—Plan of station arranged for extension. The space required for a central station depends upon the number and kind of lights to be supplied, and upon the character and arrangement of the machinery. In calculating the size of building required, two things must be carefully considered: first, the building must be adapted to the plant to be installed in the beginning; and second, it must be arranged so that enlargement can be made without disarranging or interfering with the plant already in existence. This is usually best secured by providing for expansion in one or two definite directions, the building being made large enough to accommodate additional units that will be necessary at some future time because of the growth of the community and consequent increased demand for electric current.

Fig. 2,723.—Interior of old Riverside station showing at the right, seven 6,000 horse power alternators driven by reciprocating engines, and at the left, a number of turbine units aggregating 90,000 horse power.

Fig. 2,724.—View of engine and condenser, showing how to arrange the piping to secure good vacuum. Locate the condenser as near the engine as possible; use easy bends instead of elbows; place the pump below bottom of condenser so the water will drain to pump. At A is a relief valve, for protection in case the condenser become flooded through failure of the pump, and at B is a gate valve to shut off condenser in case atmospheric exhaust is desired to permit repairs to be made to condenser during operation. A water seal should be maintained on the relief valve and special attention should be given to the stuffing box of the gate valve to prevent air leakage. The discharge valve of the pump should be water sealed.

Fig. 2,725.—"Dry pipe" for horizontal boiler: it is connected to the main outlet and its upper surface is perforated with small holes, the far end being closed. With this arrangement steam is taken from the boiler over a large area, so that it will contain very little moisture. All horizontal boilers without a dome should be fitted with a dry pipe; most engineers do not realize the importance of obtaining dry steam for engine operation.

Fig. 2,726.—Method of connecting a header to a battery of boilers. Where two or more boilers are connected to a single header, the use of a reliable non-return boiler stop valve is necessary, and in some countries their installation is compulsory. A non-return boiler stop valve will instantly close should the pressure in the boiler to which it is attached suddenly decrease below that in the header, and thereby prevent the entrance of steam from the other boilers of the battery. This sudden decrease in pressure may be caused by a ruptured fitting or the blowing out of a tube, in which event an ordinary stop valve taking the place of a non-return boiler stop valve would be inadequate, as the loss of steam from the other boilers of the battery would be tremendous before an ordinary valve could be reached and closed, assuming that it would be possible to do so, which in the majority of cases it is not. Should it be desired to cut out a boiler for cleaning or repairs, the non-return boiler stop valve will not permit steam to enter the boiler from the header, even should the handwheel be operated for this purpose, as it cannot be opened by hand, but can, however, be closed. A non-return boiler stop valve should be attached to each boiler and connected to an angle valve on the header. A pipe bend should be used for connecting the valves, as this will allow for expansion and contraction. The pipe should slope a trifle downward toward the header and a suitable drain provided. This drain should be opened and all water permitted to escape before the angle valve is opened, thereby preventing any damage due to water hammer.

Figs. 2,727 and 2,728.—Method of preventing vibration and of supporting pipes. The figures show top and side views of a main header carried in suitable frames fitted with adjustable roller. While the pipe is illustrated as resting on the adjustable rollers, nevertheless the rollers may also be placed at the sides or on top of the pipe to prevent vibration, or in cases where the thrust from a horizontal or vertical branch has to be provided for. This arrangement will take care of the vibration without in any way preventing the free expansion and contraction of the pipe.

Figs. 2,729 and 2,730.—Points on placing stop valves. The first and most important feature is to ascertain whether the valve will act as a water trap for condensed steam. Fig. 2,729 illustrates a common error in the placing of valves, as this arrangement permits of an accumulation of condensed steam above the valve when closed, and should the engineer be careless and open the valve suddenly, serious results might follow owing to water-hammer. Fig. 2,730 illustrates the correct method of placing the valve. It sometimes occurs, however, that it is not convenient to place the valve as shown in fig. 2,730 and that fig. 2,729 is the only manner in which the valve can be placed. In such cases, the valve should have a drain, and this drain should always be opened before the large valve is opened.

Fig. 2,731.—Plan of electrical station with belt drive without counter shaft. The installation here represented consists of two boilers, S, etc., and three sets of engines and generators, T, M, etc. Sufficient allowance has been made in the plans, however, for future increase of business, as additional space has been provided for an extra engine and generator set, as indicated by the dotted lines.

Fig. 2,732.—Plan of electrical station containing direct connected units. As shown, space is provided for an extra boiler and engine and generator set, as indicated by the dotted lines. Space also exists for a storage battery room if necessary, and the partition dividing this room from the engine and dynamo room is shown by a dotted line as in previous cases.

Fig. 2,733.—Angle for foundation footing. In ordinary practice the footing courses upon which the walls of the building proper rest, consist of blocks or slabs of stone as large as are available and convenient to handle. Footings of brick or concrete are also used in very soft soils; footings consisting of timber grillage are often employed. A grillage of iron or steel beams has also been used successfully. The inclination of the angle φ, of footing should be about as follows: for metal footings 75°; for stone, 60°; for concrete, 45°; for brick, 30°. Damp proof courses of slate, or layer of asphalt are laid in or on the foundations or lower walls to prevent moisture arising or penetrating by capillary attraction.

Fig. 2,734.—Concrete foundation showing method of installing the anchor bolts.

Fig. 2,735.—View showing part of template for locating anchor bolt centers, pipes through which the bolts pass and bolt boxes at lower end of bolts. The completed foundation is shown in fig. 2,734, with template removed. The template is made of plain boards upon which the center lines are drawn, and bolt center located. Holes are bored at the bolt centers to permit insertion of the pipes as shown.

Fig. 2,736.—One form of roof construction.

Fig. 2,737.—An example of direct connected unit with gas engine power. The view shows a Westinghouse 200 kva., 4,000 volt, three phase, 60 cycle alternator direct connected to a gas engine.

Fig. 2,738.—Curves showing comparative costs of chimney and mechanical draft. In certain of these, the cost of the existing chimney is known, and that of the complete mechanical draft plant is estimated, while in others, the cost of mechanical draft installation is determined from the contract price, and the expense of a chimney to produce equivalent results is calculated. Costs are shown for both single, forced and induced engine driven fans and for duplex engine driven plants, in which either fan may serve as a relay. An apparatus of the latter type is the most expensive, and finds its greatest use where economizers are employed.

Figs. 2,739 and 2,740.—Substituting mechanical draught in place of chimney. The relative proportions of a brick chimney, and of the smoke pipe required when mechanical draft is introduced are forcibly shown in the illustrations, which show the works of the B.F. Sturtevant Co., at Jamaica Plain, Mass. The removal of the boilers to a position too far distant from the existing chimney to permit of its longer fulfilling its office, led to the substitution of an induced draft fan and the subsequent removal of the chimney. The present stack or smoke pipe, barely visible in fig. 2,740, extends only 31 feet above the ground, and no trouble is experienced from smoke.

Figs. 2,741 to 2,744.—Installation of forced draft system to old boiler plant. The figures illustrate the simplest method. The fan which is of steel plate with direct connected double cylinder engine, is placed immediately over the end of a brick duct into which the air is discharged. This duct is carried under ground across the front of the boilers, to the ash pits of each of which connection is made through branch ducts. Each branch duct opening is provided with special ash pit damper, operated by notched handle bar, as illustrated in the detail. This method of introduction serves to distribute the air within the ash pit, and to secure even flow through the fuel upon the grate above. Of course, the ash pit doors must remain closed in order to bring about this result. A chimney of sufficient height to merely discharge the gases above objectionable level is all that is absolutely necessary with this arrangement. Although the introduction of a fan in an old plant is usually evidence of the insufficiency of the existing chimney to meet the requirements, such a chimney, will, however, usually serve as a discharge pipe for the gases when the fan is employed. The fan thus becomes more than a mere auxiliary to the chimney; it practically supplants it so far as the method of draught production is concerned.

Figs. 2,745 and 2,746.—Comparison of chimney draft and mechanical draft. The illustrations show a plant of 2,400 H.P. of modern water tube boilers, 12 in number, set in pairs and equipped with economizers. Fig. 2,745 indicates the location of a chimney, 9 feet in internal diameter by 180 feet high, designed to furnish the necessary draft; fig. 2,746 represents the same plant with a complete duplex induced draught apparatus substituted for the chimney, and placed above the economizer connections. Each of the two fans is driven by a special engine, direct connected to the fan shaft, and each is capable of producing draft for the entire plant. A short steel plate stack unites the two fan outlets and discharges the gases just above the boiler house roof. All of the room necessary for the chimney is saved, and no valuable space is required for the fans.

Fig. 2,747.—Forced draft plant with hollow bridge wall at the Crystal Water Co., Buffalo, N. Y. The air is delivered to the ash pit via the hollow bridge wall, being supplied under pressure by the blower seen at the side of the boiler setting. As shown, the blower is operated by a small reciprocating engine; however, compact blowing units with steam turbine drive can be had and which are designed to be placed in the boiler setting.

Fig. 2,748.—Longitudinal section of elementary Parsons type steam turbine. The turbine consists essentially of a fixed casing, or cylinder, and a revolving spindle or drum. The ends of the spindle are extended in the form of a shaft, carried in two bearings A and B, and, excepting the small parts of the governing mechanism and the oil pump, these bearings are the only rubbing parts in the entire turbine. Steam enters from the steam pipe at C and passes through the main throttle or regulating valve D, which, as actually constructed, is a balanced valve. This valve is operated by the governor through suitable controlling mechanism. The steam enters the cylinder through the passage E and, turning to the left passes through alternate stationary and revolving rows of blades, finally emerging from them at F and flowing through the connection G to the condenser or to the atmosphere, depending upon whether the turbine is condensing or non-condensing. Each row of blades, both stationary and revolving, extends completely around the turbine and the steam flows through the full annulus between the spindle and the cylinder. In an ideal turbine the lengths of the blades and the diameter of the spindle which carries them would continuously and gradually increase from the steam inlet to the exhaust. Practically, however, the desired effect is produced by making the spindle in steps, there being generally three such steps or stages, H, J and K. The blades in each step are arranged in groups of increasing length. At the beginning of each of the larger steps, the blades are usually shorter than at the end of the preceding smaller step, the change being made in such a way that the correct relation of blade length to spindle diameter is secured. The steam, acting as previously described, produces a thrust tending to force the spindle toward the left, as seen in the cut. This thrust, however, is counteracted by the "balance pistons," L, M and N, which are of the necessary diameter to neutralize the thrust on the spindle steps, H, J and K, respectively. These elements are called "pistons" for convenience, although they do not come in contact with the cylinder, but both the pistons and the cylinder are provided with alternate rings which form a labyrinth packing to retard the leakage of steam. In order that each balance piston may have the proper pressure on both sides, equalizing passages O, P and Q are provided connecting the balance pistons with the corresponding stages of the blading. The end thrust being thus practically neutralized by means of the balance pistons, the spindle "floats" so that it can be easily moved in one direction or the other. In order to definitely fix the position of the spindle, a small adjustable collar bearing is provided at R, inside the housing of the main bearing B. This collar bearing is adjustable so as to locate and hold the spindle in such position so that there will be such a clearance between the rings of the balance piston and those of the cylinder, that the leakage of steam will be reduced to a minimum and, at the same time, prevent actual contact under varying conditions of temperature. Where the shaft passes out of the cylinder, at S and T, it is necessary to provide against in-leakage of air or out-leakage of steam by means of glands. These glands are made tight by water packing without metallic contact. The shaft of the turbine is extended at U and coupled to the shaft of the alternator by means of a flexible coupling. The high pressure turbines are so proportioned that, when using steam as previously described, they have enough capacity to take care of the ordinary fluctuations of load when controlled by the governor through the valve D, thus insuring maximum economy of steam consumption at approximately the rated load. To provide for overloads, the valve V is supplied to admit steam to an intermediate stage of the turbine. This valve shown diagrammatically in the illustration, is arranged to be operated by the governor and is, according to circumstances, located either as shown by the illustration, or at another stage of the turbine.

Fig. 2,749.—Arrangement of blading in Parsons type turbine, consisting of alternate moving and stationary blades. The path taken by the steam is indicated by the arrows.

Fig. 2,750.—Sectional view of Parsons-Westinghouse turbine, showing rotor and governor.

Fig. 2,751.—Sectional view of a combination impulse and reaction single flow turbine. This is a modification of the single flow type, in which the smallest barrel of reaction blading is replaced by an impulse wheel. Steam is admitted to the nozzle block A, is expanded in the nozzles and discharged against a portion of the periphery of the impulse wheel. The intermediate and low pressure stages are identical with the corresponding stages in the single flow type. The substitution of the impulse element for the high pressure section of reaction blading has no influence one way or another on the efficiency. That is to say the efficiency of an impulse wheel is about the same at the least efficient section of reaction blading. This design is attractive, however, in that it shortens the machine materially, and gives a stiffer design of rotor. The entering steam is confined in the nozzle chamber until its pressure and temperature have been materially reduced by expanding through the nozzles. As the nozzle chamber is cast separately from the main cylinder, the temperature and pressure differences to which the cylinder is subjected are correspondingly lessened. However, probably on account of its small diameter at the high pressure section, the straight Parsons type has always shown itself to be adequate for all of the steam pressures and temperatures encountered in ordinary practice.

Fig. 2,752.—Sectional view of governor of the Parsons-Westinghouse turbine.

Fig. 2,753.—Sectional view of a double flow turbine. The maximum economical capacity of a single flow turbine is limited by the rotative speed. The economical velocity at which the steam may pass through the blades of the turbine depends on the velocity of the moving blades. The capacity of the turbine depends on the weight of the steam passed per unit of time, which in turn depends on the mean velocity and the height of the blades. For a given rotative speed, the mean diameter of blade ring practicable is limited by the allowable stresses due to centrifugal force, and there is a practical limit for the height of the blades. Now if the rotative speed be taken only half as great, the maximum diameter of the rotor may be doubled and, without increasing the height of the blades, the capacity of the turbine will be doubled. So with the single flow steam turbine as well as with the single crank reciprocating engine, there is a practical limiting economical capacity for any given speed. If this limit be reached with a single crank reciprocating engine, a unit of double the power may be produced at the same speed by coupling two single crank engines to one shaft. Similar results are secured making a double flow turbine which is in effect, as will be seen from the figure, two single flow turbines made up in a single rotor in a single casing with a common inlet and two exhausts. Steam enters the nozzle block, acts on the impulse element, and then the current divides, one-half of the steam going through the reaction blading at the left of the impulse wheel; the remainder passes over the top of the impulse wheel and through the impulse blading at the right.

Fig. 2,754.—Sectional view of a semi-double flow turbine. This is a modification in which the intermediate section of reaction blading is single flow, and the low pressure section only is double flow. This would be analogous to a four cylinder triple expansion engine, that is, one with one high pressure, one intermediate pressure and two low pressure cylinders—a design not at all uncommon in very large engines in which the required dimensions of a single low pressure cylinder would be prohibitive. Such turbines are useful for capacities greater than is desirable for a single flow turbine, and which are still below the maximum possibilities of a double flow turbine of the same speed. In such machines the best efficiency is secured by making the intermediate blading in a single section large enough to pass the entire quantity of steam. A "dummy" similar to those used on the single flow Parsons type, shown at the right of the impulse wheel, compels all of the steam to pass through the single intermediate section of the reaction blading, and balances the end thrust due to this section. When the steam issues from the intermediate section, the current is divided, one-half passing directly to the adjacent low pressure section, while the other half passes through the holes shown in the periphery of the hollow rotor and through the rotor itself, beyond the dummy ring, into the other low pressure section at the left hand end of the turbine.

Fig. 2,755.—Westinghouse valve gear with steam relay. In the smaller turbines, the governor acts directly on the steam admission valves, opening first the primary valve, and then, if necessary, the secondary valve, after the primary is fully open. In turbines of the single flow Parsons type, the governor actuates two small valves controlling ports leading to steam relay cylinders which operate the admission valves. The little valve controlling the relay cylinder for the secondary valve has more lap than the other and consequently does not come into action until the primary valve has attained its maximum effective opening. The figure shows the general design of this type of valve gear.

Figs. 2,756 and 2,757.—Westinghouse valve gear with oil relay. Governors for the larger turbines, particularly those of the combination impulse and reaction double, or single double flow type, employ an oil relay mechanism, as shown in the figure, for operating the steam valves. In these turbines the lubricating oil circulating pump, maintains a higher pressure than is required for the lubricating system. The governor controls a small relay valve A which admits pressure oil to, or exhausts it from the operating cylinder. When oil is admitted to the operating cylinder raising the piston, the lever C lifts the primary valve E. The lever D moves simultaneously with C, but on account of the slotted connection with the stem of the secondary valve F, the latter does not begin to lift until the primary valve is raised to the point at which its effective opening ceases to be increased by further upward travel. In the Westinghouse designs, the operating valve, A is connected not only to the governor, but also to a vibrator, which gives it a slight but continuous reciprocating motion, while the governor controls its mean position. The effect of this is manifested in a slight pulsation throughout the entire relay system, which, so to speak, keeps it "alive" and ready to respond instantly, to the smallest change in the position of the governor. The oil relay can be made sufficiently powerful to operate valves of any size, and it is also in effect a safety device in that any failure of the lubricating oil supply will automatically and immediately shut off the steam and stop the turbine.

Fig. 2,758.—Elevation of new turbine central station erected by the Boston Edison Co. The turbine room is 68 feet, 4 inches wide and 650 feet long from outside to outside of the walls. The boiler room is 149 feet, 6 inches by 640 feet and equipped with twelve groups of boiler, one group consisting of eight 512 H.P. boilers for each turbine. The switching arrangements are located in a separate building as shown in the elevation. The total floor space covered by boiler room, turbine room and switchboard room is 2.64 square feet per kw. The boilers are all on the ground floor. See fig. 2,714 for plan.

Fig. 2,759.—Illustration of a weir. To make a weir, place a board across the stream at some point which will allow a pond to form above. The board should have a notch cut in it with both side edges and the bottom sharply beveled toward the intake, as shown in the above cut. The bottom of the notch, which is called the "crest" of the weir, should be perfectly level and the sides vertical. In the pond back of the weir, at a distance not less than the length of the notch, drive a stake near the bank, with its top precisely level with the crest. By means of a rule, or a graduated stake as shown, measure the depth of water over the top of stake, making allowance for capillary attraction of the water against the sides of the weir. For extreme accuracy this depth may be measured to thousandths of a foot by means of a "hook gauge," familiar to all engineers. Having ascertained the depth of water over the stake, refer to the accompanying table, from which may be calculated the amount of water flowing over the weir. There are certain proportions which must be observed in the dimensions of this notch. Its length, or width, should be between four and eight times the depth of water flowing over the crest of the weir. The pond back of the weir should be at least fifty per cent. wider than the notch and of sufficient width and depth that the velocity of flow or approach be not over one foot per second. In order to obtain these results it is advisable to experiment to some extent.

Figs. 2,760 and 2,761.—Samson vertical runner and shaft, and complete Samson vertical turbine. The runner is composed of two separate and distinct types of wheel, having thereby also two diameters. Each wheel or set of buckets receives its separate quantity of water from one and the same set of guides, but each set acts only once and singly upon the water used, and the water does not act twice upon the combined wheel, as some suppose. In construction, the lower or main set of buckets is made of flanged plate steel, and cast solidly into a heavy ring surrounding the outer and lower edges, and into a heavy diaphragm, separating the two sets of buckets.

Fig. 2,762.—Water discharging from a needle nozzle due to a pressure of 169 lbs. per sq. in.

Fig. 2,763.—Photograph of an operating tangential water wheel equipped with Pelton buckets.

Fig. 2,764.—Sectional elevation of one of the 5,000 horse power vertical Pelton-Francis turbines directly connected to generator, as installed for the Schenectady Power Co.

Figs. 2,765 to 2,768.—Cross sections of Lowel dam power house, and wheel pits containing sixteen Samson turbines: The section C-D gives an end view of the generator room showing the locations of the generators below the head level water. They are secure against flood water, or leakage, by well constructed stuffing boxes in the iron bulkheads, through which the turbine wheel shafts pass and connect to the generators. Section E-F gives an end view of one of these wheel rooms or penstocks, and shows the extension of the draft tube from wheel case into tail water. The section A-B shows the sub-structure of gravel and macadam under the controlling gates, this forming also a portion or extension of the dam proper. These gates turn on an axis made of two 15 inch I beams securely riveted together with plates and angle irons to which the wooden frame is attached. The radius of the gates is 14 feet. They are designed to allow the water to pass underneath the gate, thus controlling any height of head water. They are intended to take care of an excess of water at unusual stages of the river. The whole affair has been well designed and executed. This plant furnishes a good example of a secure, and level foundation, since the wheel houses and generator room are immediately on the rock. It is necessary in all tandem plants to provide a very secure, substantial super-structure so that the long line of turbines and shaft will always remain straight and in proper alignment with the generator and the turbine cases. Users cannot be reminded of this too often.

Figs. 2,769 and 2,770.—Exterior and interior of hydro-electric plant at Harrisburg, Va. It is located on the south fork of the Shenandoah River, twelve and one-half miles distant. A dam 720 feet long and 15 feet high was built on a limestone ledge running across the river; which with a fall of 5 feet from the dam to the power house, a quarter of a mile distant, secured an effective head pressure of 20 feet. The power house, comprising the generator room and the wheel room, also the machinery room, are here shown. The wheel room, which is 20 × 40 feet, extends across the head race, and rests upon solid concrete walls, forming the sides and ends of the wheel pits. The end wall is 6 feet thick at the bottom, and 4½ feet at the top. It has three arched openings, each 8 feet wide and 9 feet high, through which the water escapes after leaving the turbines. The intake is protected by a wrought iron rack 40 feet long. The power is obtained by three 50 inch vertical shaft Samson turbines, with a 20 inch Samson for an exciter. The three large turbines have a rating of 1,350 horse power; and are connected to the main horizontal line shaft by bevel mortise gears 7 feet diameter and 15 inches face. The couplings on the main shaft have 48 inch friction clutch hubs, permitting either or each turbine being operated, or shut down independently of the others. The main shaft is 85 feet long and 6 inches diameter; making 280 revolutions. This shaft carries two pulleys 70 inches diameter and 38 inches face for driving the generators. The accompanying illustration shows the harness work, gears, pulleys, etc., furnished with the turbines. The 20 inch horizontal shaft Samson turbine of 72 horse power is direct connected to an exciter generator of 20 kw., running 700 rev. per min. The two large generators are driven 450 revolutions per minute by belts producing a three phase current of 60 cycles of 11,500 volts for the twelve and one-half miles transmission. The line consists of three strands of No. 4 bare copper wire. This current is used for lighting and power purposes, and the plant is of the latest improved design and construction.

Fig. 2,769a.—Triumph direct current generator set with upright slide valve engine.

Fig. 2,770a.—Murray alternating current direct connected unit with high speed Corliss engine and belt driven exciter, 50, 75 and 100 kva. alternator and 150 R.P.M. engine.

Fig. 2,771.—Direct connected direct current unit with Ridgway high speed four valve engine.

Fig. 2,772.—Buckeye mobile, or self contained unit consisting of compound condensing engine, boiler, superheater, reheater, feed and air pumps; it produces one horse power on 1½ lbs. of coal, built in sizes from 75 to 600 horse power.

Fig. 2,773.—Westinghouse three cylinder gas engine, direct connected to dynamo, showing application of gas engine drive for small direct connected units.

Fig. 2,774.—General Electric 25 kw., gasoline electric generating set for lighting and power. The engine has four cylinders 7¼ × 7½, and runs at a speed of 560 revolutions per minute. The total candle power capacity in Mazda lamps is 20,000. The ignition is by low tension magneto, coil and battery. Carburetter is of the constant level type to which gasoline is delivered by a pump driven by the engine. Forced lubrication; five crank shaft bearings babbitted; valves in side; overall dimensions 96 × 34 × 60 high; weight 5,000.

Fig. 2,775.—Plan of sub-station with air blast transformers and motor operated oil switches and underground 11,000 or 13,200 volt high tension lines.

Fig. 2,776.—Plan of small sub-station with single phase oil insulated self-cooling transformers and hand operated oil switches 11,000 or 13,200 volts, overhead high tension lines.

Fig. 2,777.—Elevation of small sub-station, as shown in plan in Fig. 2,776.

Fig. 2,778.—Marine portable transformer station on Los Angeles Aqueduct. The view shows three 20 kva. Westinghouse out door transformers installed on a float, 33,000 volts high pressure; 440 volts low pressure; 50 cycles.

Ques. Explain the use of reactance coils in sub-stations.

Ans. In order that the direct current voltage of the ordinary rotary may be regulated by a field rheostat, which calls for a corresponding change in the alternating current voltage, a reactance coil is provided between the low tension winding and the converter.

Without such a reactance the maintenance of the same voltage at full load as at no load involves excessive leading and lagging currents and consequently excessive heating in the armature inductors, unless 1985 the resistance drop from the source of constant pressure is small, or the natural reactance of the circuit high.

Ques. What is the effect of weakening the converter field?

Ans. A lagging current is set up which causes a drop in the reactance coil.

Fig. 2,779.—Sectional elevation of portable outdoor transformer type sub-station. The high voltage switching and protective apparatus is mounted, out of the way, on the roof of the car, but is operated from the switchboard with a standard remote control handle. The transformer is carried directly over the truck at the uncovered end of the car and the low-tension leads from it run in conduit beneath the floor and up into the cab, (which contains the converter and switchboard) to the converter. The positive lead runs through a conduit and ends in a terminal on the roof. The energy thus makes a complete circuit of the car leaving at a point close to that at which it entered. The low pressure alternating current as well as the direct current positive leads are carried below the car floor in iron conduit supported from the channel frame. The field wires are carried through this conduit to the rheostat. Wiring for the lights is arranged to supply two, 5 light clusters. One is fed with the 600 volt direct current and the other with 420 volt alternating current. All lighting conductors are carried in metal moulding carried between the flanges of the channel iron ribs. High wiring is carried entirely on the roof of the car where it is entirely out of the way and where the operator cannot come in contact with it. The switchboard should be of the utmost simplicity. Usually the negative and equalizer switches, and the field break-up switch are mounted on the frame of the converter. The double throw switch for starting and running the converter can be mounted under the floor of the car and operated by handle at the switchboard. The rheostat can be mounted back of the switchboard on brackets bolted to the car super-structure. The switchboard need only carry the positive knife switch and circuit breaker, and the alternating current ammeter, voltmeter and power factor meter. Sometimes a watthour meter is added. The positive lead is brought out through a conduit on the roof of the car and is arranged for bolting to the positive feeder. The negative and equalizer terminals are located at the cab end of the car and are arranged so that connection can be easily made from them to the ground and, if necessary, to an equalizer circuit. There is usually a sliding door at each end of the cab and two windows on each side. Above the doors, transoms, extending the width of the cab, are arranged to drop so that a current of air will circulate through the cab under the roof, carrying out the heated air. There are also several ventilating holes beneath the converter in the floor of the car. These provisions insure a constant circulation of air through the car which carries away all heated air.

1986 Ques. State the effect of strengthening converter field.

Ans. A leading current is set up which gives a rise of voltage in the reactance coil.

Hence when a heavy current passes through the series coil of a compound wound converter and tends to produce a leading current, the reactance coil will balance it, and improve the power factor of the whole line.

Fig. 2,780.—Westinghouse 300 kw. converter in portable sub-station.

Portable Sub-Stations.—A portable sub-station constitutes a spare equipment for practically any number of permanent sub-stations and renders unnecessary the installation of spare equipment in each. 1987

It can be used to increase the capacity of a permanent sub-station when the load is unusually heavy, or to provide service while a permanent sub-station is being overhauled or rebuilt.

The transformer can be used for emergency lighting, the primary being connected to a high pressure line and the secondary to the load, if special provision be made at the time the transformer is built to adapt it for these applications.

Fig. 2,781.—Switchboard end of Westinghouse portable sub-station.

When an electric railway has a portable sub-station, direct current can be provided at any point on the system where there is track at the high pressure line. The direct current can be made available very 1988 quickly as its production involves only the transferring of the sub-station, and its connection to the high pressure line.

Portable sub-stations range in capacity from 200 to 500 kw., and for all alternating current voltages up to 66,000, and frequencies of 25 and 60 cycles.

Although portable sub-stations usually must be of more or less special design to adapt them to the conditions under which they must operate, there are certain general features that are common to all. All members are readily accessible and there are no unnecessary parts. The weight and dimensions are a minimum insuring ease of transportation. Live parts are so protected that the danger of accidental contact with them is minimized.

Figs. 2,782 and 2,783.—Views of levelling device for Westinghouse converter.

Ques. What are the advantages of using outdoor transformers on portable sub-stations?

Ans. All high pressure wiring is kept out of the car. The transformer is more effectively cooled and the heat dissipated by the transformer does not warm the interior of the cab. The transformer is much more accessible. The car can be run under a crane and the transformer coils pulled out with a hoist.

Taps for different high and low pressure voltages can be readily provided at the time the transformer is being built.

1989

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CHAPTER LXVII
MANAGEMENT

The term "management," broadly speaking, includes not only the actual skilled attention necessary for the proper operation of the machines, after the plant is built, but also other duties which must be performed from its inception to completion, and which may be classified as

   1. Selection;
   2. Location;
   3. Erection;
   4. Testing;
   5. Running;
   6. Care;
   7. Repair.

That is to say, someone must select the machinery, determine where each machine is to be located, install them, and then attend to the running of the machines and make any necessary repairs due to the ordinary mishaps likely to occur in operation.

These various duties are usually entrusted to more than one individual; thus, the selection and location of the machinery is done by the designer of the plant, and requires for its proper execution the services of an electrical engineer, or one possessing more than simply a practical knowledge of power plants. 1990

The erection of the machines is best accomplished by those making a specialty of this line of work, who by the nature of the undertaking acquire proficiency in methods of precision and an appreciation of the value of accuracy which is so essential in the work of aligning the machines, and which if poorly done will prove a constant source of annoyance afterward.

The attention required for the operation of the machines, embracing the running care and repair, is left to the "man in charge," who in most cases of small and medium size plants is the chief steam engineer. He must therefore, not only understand the steam apparatus, but possess sufficient knowledge of electrical machinery to operate and maintain it in proper working order.

The present chapter deals chiefly with alternating current machinery, the management of direct current machines having been fully explained in Guide No. 3, however, some of the matter here presented is common to both classes of apparatus.

Selection.—In order to intelligently select a machine so that it will properly harmonize with the conditions under which it is to operate, there are several things to be considered.

   1. Type;
   2. Capacity;
   3. Efficiency;
   4. Construction.

The general type of machine to be used is, of course, dependent on the system employed, that is, whether it be direct or alternating, single or polyphase.

Thus, the voltage in most cases is fixed except on transformer systems where a choice of voltage may be had by selecting a transformer to suit. 1991

In alternating current constant pressure transmission circuits, an average voltage of 2,200 volts with step down transformer ratios of ¹⁄₁₀ and ¹⁄₂₀ is in general use, and is recommended.

For long distance, the following average voltages are recommended 6,000; 11,000; 22,000; 33,000; 44,000; 66,000; 88,000; and higher, depending on the length of the line and degree of economy desired.

In alternating circuits the standard frequencies are 25, and 60 cycles. These frequencies are already in extensive use and it is recommended to adhere to them as closely as possible.

Fig. 2,784.—Diagram of connections for testing to obtain the saturation curve of an alternator. The saturation curve shows the relation between the volts generated in the armature and the amperes of field current (or ampere turns of the field) for a constant armature current. The armature current may be zero, in which case the curve is called no load saturation curve, or sometimes the open circuit characteristic curve. A saturation curve may be taken with full load current in the armature; but this is rarely done, except in alternators of comparatively small output. If a full load saturation curve be desired, it can be approximately calculated from the no load saturation curve. The figure shows the connections. If the voltage generated is greater than the capacity of the voltmeter, a multiplying coil or a step down pressure transformer may be used, as shown. A series of observations of the voltage between the terminals of one of the phases, is made for different values of the field current. Eight or nine points along the curve are usually sufficient, the series extending from zero to about fifty per cent. above normal rated voltage. The points should be taken more closely together in the vicinity of normal voltage than at other portions of the curve. Care must be taken that the alternator is run at its rated speed, and this speed must be kept constant. Deviations from constant speed may be most easily detected by the use of a tachometer. If the machine be two phase or three phase, the voltmeter may be connected to any one phase throughout a complete series of observations. The voltage of all the phases should be observed for normal full load excitation by connecting the voltmeter to each phase successively, keeping the field current constant at normal voltage. This is done in order to see how closely the voltage of the different phases agree.

In fixing the capacity of a machine, careful consideration should be given to the conditions of operation both present and future in order that the resultant efficiency may be maximum.

Most machines show the best efficiency at or near full load. If the load be always constant, as for instance, a pump forcing water to a 1992 given head, it would be a simple matter to specify the proper size of machine, but in nearly all cases, and especially in electrical plants, the load varies widely, not only the daily and hourly fluctuations, but the varying demands depending on the season of the year and growth of the plant's business. All of these conditions tend to complicate the matter, so that intelligent selection of capacity of a machine requires not only calculation but mature judgment, which is only obtained by long experience.

Fig. 2,785.—Saturation curve taken from a 2,000 kw., three phase alternator of the revolving field type, having 16 poles, and generating 2,000 volts, and 576 amperes per phase when run at 300 R.P.M.

In selecting a machine, or in fact any item connected with the plant its construction should be carefully considered.

Standard construction should be insisted upon so that in the event of damage a new part can be obtained with the least possible delay.

The parts of most machines are interchangeable, that is to say, with the refined methods of machinery a duplicate part (usually carried in stock) may be obtained at once to replace a defective or broken part, and made with such precision that little or no fitting will be required.

1993 The importance of standard construction cannot be better illustrated than in the matter of steam piping, that is, the kind of fittings selected for a given installation.

With the exception of the exhaust line from engine to condenser, where other than standard construction may sometimes be used to reduce the frictional resistance to the steam, the author would adhere to standard construction except in very exceptional cases. Those who have had practical experience in pipe fitting will appreciate the wisdom of this.

For installations in places remote from large supply houses, the more usual forms of standard fittings should be employed, such as ordinary T's, 45° and 90° elbows, etc.

In such locations, where designers specify the less usual forms of standard fittings such as union fittings, offset reducers, etc., or special fittings made to sketch, it simply means, in the first instance that they usually cannot be obtained of the local dealer, making it necessary to order from some large supply house and resulting in vexatious delays.

As a rule, those who specify special fittings have found that their making requires an unreasonable length of time, and the cost to be several times that of the equivalent in standard fittings.

An examination of a few installations will usually show numerous special and odd shape fittings, which are entirely unnecessary.

Moreover, a standard design, in general, is better than a special design, because the former has been tried out, and any imperfection or weakness remedied, and where thousands of castings of a kind are turned out, a better article is usually the result as compared with a special casting. 1994

In the matter of construction, in addition to the items just mentioned, it should be considered with respect to

   1. Quality;
   2. Range;
   3. Accessibility;
   4. Proportion;
   5. Lubrication;
   6. Adjustment.

It is poor policy, excepting in very rare instances, to buy a "cheap" article, as, especially in these days of commercial greed, the best is none too good.

Figs. 2,786 and 2,787.—Wheel and roller pipe cutters illustrating range. The illustrations show the comparative movements necessary with the two types of cutter to perform their function. The wheel cutter requiring only a small arc of movement will cut a pipe in an inaccessible place as shown, which with a roller cutter would be impossible. Accordingly, the wheel cutter is said to have a greater range than the roller cutter.

Perhaps next in importance to quality, at least in most cases, is range. This may be defined as scope of operation, effectiveness, or adaptability. The importance of range is perhaps most pronounced in the selection of tools, especially for plants remote from repair shops.

For instance, in selecting a pipe cutter, there are two general classes: wheel cutters, and roller cutters. A wheel cutter has three wheels and a roller cutter one wheel and two rollers, the object of 1995 the rollers being to keep the wheel perpendicular to the pipe in starting the cut and to reduce burning. It must be evident that in operation, a roller cutter requires sufficient room around the pipe to permit making a complete revolution of the cutter, whereas, with a wheel cutter, the work may be done by moving the cutter back and forth through a small arc, as illustrated in figs. 2,786 and 2,787. Thus a wheel cutter has a greater range than a roll cutter.

Range relates not only to ability to operate in inaccessible places but to the various operations that may be performed by one tool.

PROPERTIES OF STANDARD WROUGHT IRON PIPE

Diameter.			Thick- ness.	Circumference.		Transverse areas.
Nominal  internal.	Actual  external.	Actual  internal.		External.	Internal.	External.	Internal.	Metal.
Inches	Inches	Inches	Inches	Inches	Inches	Sq. ins.	Sq. ins.	Sq. ins.
⅛	.405	.27	.068	1.272	.848	.129	.0573	.0717
¼	.54	.364	.088	1.696	1.144	.229	.1041	.1249
⅜	.675	.494	.091	2.121	1.552	.358	.1917	.1663
½	.84	.623	.109	2.639	1.957	.554	.3048	.2492
¾	1.05	.824	.113	3.299	2.589	.866	.5333	.3327
1	1.315	1.048	.134	4.131	3.292	1.358	.8626	.4954
1¼	1.66	1.38	.14	5.215	4.335	2.164	1.496	.668
1½	1.9	1.611	.145	5.969	5.061	2.835	2.038	.797
2	2.375	2.067	.154	7.461	6.494	4.43	3.356	1.074
2½	2.875	2.468	.204	9.032	7.753	6.492	4.784	1.708
3	3.5	3.067	.217	10.996	9.636	9.621	7.388	2.243
3½	4.	3.548	.226	12.566	11.146	12.566	9.887	2.679
4	4.5	4.026	.237	14.137	12.648	15.904	12.73	3.174
4½	5.	4.508	.246	15.708	14.162	19.635	15.961	3.674
5	5.563	5.045	.259	17.477	15.849	24.306	19.99	4.316
6	6.625	6.065	.28	20.813	19.054	34.472	28.888	5.584
7	7.625	7.023	.301	23.955	22.063	45.664	38.738	6.926
8	8.625	7.982	.322	27.096	25.076	58.426	50.04	8.386
9	9.625	8.937	.344	30.238	28.076	72.76	62.73	10.03
10	10.75	10.019	.366	33.772	31.477	90.763	78.839	11.924
11	12.	11.25	.375	37.699	35.343	113.098	99.402	13.696
12	12.75	12.	.375	40.055	37.7	127.677	113.098	14.579

PROPERTIES OF STANDARD WROUGHT IRON PIPE
(Continued)

Diam.	Length of pipe per square foot of		Length of pipe per  containing  one cubic foot.	Nominal  weight per foot.	Number of  threads per inch.
Nominal  internal.	External  surface	Internal  surface
Inches	Feet.	Feet.	Feet.	Pounds.
⅛	9.44	14.15	2513.	.241	27
¼	7.075	10.49	1383.3	.42	18
⅜	5.657	7.73	751.2	.559	18
½	4.547	6.13	472.4	.837	14
¾	3.637	4.635	270.	1.115	14
1	2.904	3.645	166.9	1.668	11½
1¼	2.301	2.768	96.25	2.244	11½
1½	2.01	2.371	70.66	2.678	11½
2	1.608	1.848	42.91	3.609	11½
2½	1.328	1.547	30.1	5.739	8
3	1.091	1.245	19.5	7.536	8
3½	.955	1.077	14.57	9.001	8
4	.849	.949	11.31	10.665	8
4½	.764	.848	9.02	12.34	8
5	.687	.757	7.2	14.502	8
6	.577	.63	4.98	18.762	8
7	.501	.544	3.72	23.271	8
8	.443	.478	2.88	28.177	8
9	.397	.427	2.29	33.701	8
10	.355	.382	1.82	40.065	8
11	.318	.339	1.450	45.95	8
12	.299	.319	1.27	48.985	8

Open construction should be employed, wherever possible, so that all parts of a machine that require attention, or that may become deranged in operation, may be accessible for adjustment or repair. 1996

The design should be such that there is ample strength, and the bearings for moving parts should be of liberal proportions to avoid heating with minimum attention.

A comparison of the proportions used by different manufacturers for a machine of given size might profitably be made before a selection is made.

The matter of lubrication is important.

Fast running machines, such as generators and motors, should be provided with ring oilers and oil reservoirs of ample capacity, as shown in figs. 2,788 to 2,794.

Fig. 2,788.—Sectional view showing a ring oiler or self oiling bearing. As shown the pedestal or bearing standard is cored out to form a reservoir for the oil. The rings are in rolling contact with the shaft, and dip at their lower part into the oil. In operation, oil is brought up by the rings which revolve because of the frictional contacts with the shaft. The oil is in this way brought up to the top of the bearing and distributed along the shaft gradually descending by gravity to the reservoir, being thus used over and over. A drain cock, is provided in the base so that the oil may be periodically removed from the reservoir and strained to remove the accumulation of foreign matter. This should be frequently done to minimize the wear of the bearing.

All bearings subject to appreciable wear should be made adjustable so that lost motion may be taken up from time to time and thus keep the vibration and noise of operation within proper limits. 1997

Selection of Generators.—This is governed by the class of work to be done and by certain local conditions which are liable to vary considerably for different stations.

These variable factors determine whether the generators must be of the direct or alternating current type, whether they must be wound to develop a high or a low voltage, and whether their outputs in amperes must be large or small. Sufficient information has already been given to cover these various cases; there are, however, certain general rules that may advantageously be observed in the selection of generators designed to fill any of the aforementioned conditions, and it is well to possess certain facts regarding their construction.

Figs. 2,789 to 2,794.—Self oiling self aligning bearing open. Views showing oil grooves, rings, bolts etc.

Ques. Name an important point to be considered in selecting a generator.

Ans. Its efficiency.

Ques. What are the important points with respect to efficiency?

Ans. A generator possessing a high efficiency at the average load is more desirable than a generator showing a high efficiency at full load. 1998

Ques. Why?

Ans. The reason is that in station practice the full load limit is seldom reached, the usual load carried by a generator ordinarily lying between the one-half and three-quarter load points.

Ques. How do the efficiencies of large and small generators compare?

Ans. There is little difference.

Fig. 2,795.—Rotor of Westinghouse type T turbine dynamo set. The dynamo is of the commutating pole type either shunt or compound wound. The turbine is of the single wheel impulse type. The wheel is mounted directly on the end of the shaft as shown. Steam is used two or more times on the wheel to secure efficiency. A fly ball governor is provided with weights hung on hardened steel knife edges. In case of over speeding, an automatic safety stop throttle valve is tapped shutting off the steam supply. This type of turbine dynamo set is especially applicable for exciter service in modern, superheated steam generating stations where the steam pressure exceeds 125 pounds. Westinghouse Type T turbines operate directly (that is, without a reducing valve) on pressures up to 200 pounds per square inch with steam superheated to 150 degrees Fahrenheit.

Ques. How are the sizes and number of generator determined?

Ans. The sizes and number of generator to be installed should be such as to permit the engines operating them being worked at nearly full load, because the efficiencies of the latter machines decrease rapidly when carrying less than this amount. 1999

Ques. What is understood by regulation?

Ans. The accuracy and reliability with which the pressure or current developed in a machine may be controlled.

It is generally possible if purchasing of a reputable concern, to obtain access to record sheets on which may be found results of tests conducted on the generator in question, and as these are really the only means of ascertaining the values of efficiency and regulation, the purchaser has a right to inspect them. If, for some reason or other, he has not been afforded this privilege, he should order the machine installed in the station on approval, and test its efficiency and regulation before making the purchase.

Fig. 2,796.—Cross section of electrical station showing small traveling crane.

Installation.—The installation of machines and apparatus in an electrical station is a task which increases in difficulty with the size of the plant. When the parts are small and comparatively light they may readily be placed in position, either by hand, by erecting temporary supports which may be moved from place to place as 2000 desired, or by rolling the parts along on the floor upon pieces of iron pipe. If, however, the parts be large and heavy, a traveling crane such as shown in fig. 2,797, becomes necessary.

Ques. What precaution should be taken in moving the parts of machines?

Ans. Care should be taken not to injure the bearings and shafts, the joints in magnetic circuits such as those between frame and pole pieces, and the windings on the field and armature.

Fig. 2,797.—Cross section of electrical station showing a traveling crane for the installation or removal of large and heavy machine parts. A traveling crane consists of an iron beam which, being supplied with wheels at the ends, can be made to move either mechanically or electrically upon a track running the entire length of the station. This track is not supported by the walls of the building, but rests upon beams specially provided for the purpose. In addition to the horizontal motion thus obtained, another horizontal motion at right angles to the former is afforded by means of the carriage which, being also mounted on wheels, runs upon a track on the top of the beam. Electrical power is generally used to move the carriage and also the revolving drums contained thereon, the latter of which give a vertical motion to the main hoist or the auxiliary hoist, these hoists being used respectively for raising or lowering heavy or light loads. In the larger sizes of electric traveling crane, a cage is attached to the beam for the operator, who, by means of three controllers mounted in the cage, can move a load on either the main or auxiliary hoist in any direction.

The insulations of the windings are perhaps the most vital parts of a generator, and the most readily injured. The prick of a pin or tack, 2001 a bruise, or a bending of the wires by resting their weight upon them or by their coming in contact with some hard substance, will often render a field coil or an armature useless.

Owing to its costly construction, it is advisable when transporting armatures by means of cranes to use a wooden spreader, as shown in fig. 2,798 to prevent the supporting rope bruising the winding.

Fig. 2,798.—View of armature in transit showing use of a wooden spreader as a protection. If a chain be used in place of the rope, a padding of cloth should be placed around the armature shaft and special care taken that the chain does not scratch the commutator.

Ques. If an armature cannot be placed at once in its final position what should be done?

Ans. It may be laid temporarily upon the floor, if a sheet of cardboard or cloth be placed underneath the armature as a protection for the windings; in case the armature is not to be used for some time, it is better practice to place it in a horizontal position on two wooden supports near the shaft ends. 2002

Ques. What kind of base should be used with a belt driven generator or motor?

Ans. The base should be provided with V ways and adjusting screws for moving the machine horizontally to take up slack in the belt, as shown in fig. 2,799.

Owing to the normal tension on the belt, there is a moment exerted equal in amount to the distance from the center of gravity of the machine to the center of the belt, multiplied by the effective pull on the belt. This force tends to turn the machine about its center of gravity. By placing the screws as shown, any turning moment, as just mentioned, is prevented.

Fig. 2,799.—Plan of belt drive machine showing V ways and adjusting screws for moving the machine forward from the engine or counter shaft to take up slack in the belt.

Ques. How should a machine be assembled?

Ans. The assembling should progress by the aid of a blue print, or by the information obtained from a photograph of the complete machine as it appears when ready for service. Each part should be perfectly 2003 clean when placed in position, especially those parts between which there is friction when the machine is in operation, or across which pass lines of magnetic force; in both cases the surfaces in contact must be true and slightly oiled before placing in position.

Contact surfaces forming part of electrical circuits must also be clean and tightly screwed together. An important point to bear in mind when assembling a machine is, to so place the parts that it will not be necessary to remove any one of them in order to get some other part in its proper position. By remembering this simple rule much time will be saved, and in the majority of instances the parts will finally be better fitted together than if the task has to be repeated a number of times.

When there are two or more parts of the machine similarly shaped, it is often difficult to properly locate them, but in such cases notice should be taken of the factory marks usually stamped upon such pieces and their proper places determined from the instructions sent with the machine.

Figs. 2,800 to 2,802.—Starrett's improved speed indicator. In construction, the working parts are enclosed like a watch. The graduations show every revolution, and with two rows of figures read both right and left as the shaft may run. While looking at the watch, each hundred revolutions may be counted by allowing the oval headed pin on the revolving disc to pass under the thumb as the instrument is pressed to its work. A late improvement in this indicator consists in the rotating disc, which, being carried by friction may be moved to the starting point where the raised knobs coincide. When the spindle is placed in connection with the revolving shaft, pressing the raised knob with the thumb will prevent the disc rotating, while the hand of the watch gets to the right position to take the time. By releasing the pressure the disc is liberated for counting the revolutions of the shaft when every 100 may be noted by feeling the knob pass under the thumb lightly pressed against it, thus relieving the eye, which has only to look on the watch to note the time.

Ques. What should be noted with respect to speed of generator?

Ans. Each generator is designed to be run at a certain speed 2004 in order to develop the voltage at which the machine is rated. The speed, in revolutions per minute, the pressure in volts, and the capacity or output in watts (volts × amperes) or in kilowatts (thousands of watts) are generally stamped on a nameplate screwed to the machine.

This requirement frequently requires calculations to be made by the erectors to determine the proper size pulleys to employ to obtain the desired speed.

Fig. 2,803.—Home made belt clamp. It is made with four pieces of oak of ample size to firmly grip the belt ends where the bolts are tightened. The figure shows the clamp complete and in position on the belt and clearly illustrates the details of construction. In making the long bolts the thread should be cut about three-quarter length of bolt and deep enough so that the nuts will easily screw on.

Example.—What diameter of engine pulley is required to run a dynamo at a speed of 1,450 revolutions per minute the dynamo pulley being 10 inches in diameter and the speed of engine, 275 revolutions per minute?

The diameter of pulley required on engine is 10 × (1,450 ÷ 275) = 53 inches, nearly.

Rule.—To find the diameter of the driving pulley, multiply the speed of the driven pulley by its diameter, divide the product by the speed of the driver and the answer will be the size of the driver required. 2005

Example.—If the speed of an engine be 325 revolutions per minute, diameter of engine pulley 42 inches, and the speed of the dynamo 1,400 revolutions per minute, how large a pulley is required on dynamo?

The size of the dynamo pulley is 42 × (325 ÷ 1,400) = 9¾ inches.

Rule.—To find the size of dynamo pulley, multiply the speed of engine by the diameter of engine wheel and divide the product by the speed of the dynamo.

Figs. 2,804 and 2,805.—A good method of lacing a belt. The view at the left shows outer side of belt, and at the right, inner or pulley side.

Example.—If a steam engine, running 300 revolutions per minute, have a belt wheel 48 inches in diameter, and be belted to a dynamo having a pulley 12 inches in diameter, how many revolutions per minute will the dynamo make?

The speed of dynamo will be 300 × (48 ÷ 12) = 1,200 rev. per min.

Rule.—When the speed of the driving pulley and its diameter are known, and the diameter of the driven pulley is known, the speed of the driven pulley is found by multiplying the speed of the driver by its diameter in inches and dividing the product by the diameter of the driven pulley. 2006

Example.—What will be the required speed of an engine having a belt wheel 46 inches in diameter to run a dynamo 1,500 revolutions per minute, the dynamo pulley being 11 inches in diameter?

The speed of the engine is 1,500 × (11 ÷ 46) = 359 rev. per min. nearly.

Fig. 2,806.—Wiring diagram and directions for operating Holzer-Cabot single phase self-starting motor. Location: The motor should be placed in as clear and dry a location as possible, away from acid or other fumes which would attack the metal parts or insulation, and should be located where it is easily accessible for cleaning and oiling. Erection: The motor should be set so that the shaft is level and parallel with the shaft it is to drive so that the belt will run in the middle of the pulleys. Do not use a belt which is too heavy or too tight for the work it has to do, as it will materially reduce the output of the motor. The belt should be from one-half to one inch narrower than the pulley. Rotation: In order to reverse the direction of rotation, interchange leads A and B. Suspended Motors: Motors with ring oil bearings may be used on the wall or ceiling by taking off end caps and revolving 90 or 180 degrees until the oil wells come directly below the bearings. Starting: Motors are provided with link across two terminals on the upper right hand bracket at the front of the motor and with this connection should start considerable overloads. If the starting current be too great with this connection, it may be reduced by removing the link. Temperatures: At full load the motor will feel hot to the hand, but this is far below the danger point. If too hot for touch, measure temperature with a thermometer by placing bulb against field winding for 10 minutes, covering thermometer with cloth or waste. The temperature should not exceed 75 degrees Fahr. above the surrounding air. Oiling: Fill the oil wells to the overflow before starting and keep them full. See that the oil rings turn freely with shaft. Care: The motor must be kept clean. Smooth collector rings with sandpaper and see that the brushes make good contact. When brushes become worn they may be reversed. When fitting new brushes or changing them always sandpaper them down until they make good contact with the collector rings, by passing a strip of sandpaper beneath the brush.

2007

Rule.—To find the speed of engine when diameter of both pulleys, and speed of dynamo are given, multiply the dynamo speed by the diameter of its pulley and divide by the diameter of engine pulley.

Ques. How are the diameters and speeds of gear wheels figured?

Ans. The same as belted wheels, using either the pitch circle diameters or number of teeth in each gear wheel.

Figs. 2,807 to 2,809.—Wiring diagrams and directions for operating Holzer-Cabot slow speed alternating current motors. Erecting: In installing the motor, be sure the transformer and wiring to the motor are large enough to permit the proper voltage at the terminals. If too small, the voltage will drop and reduce the capacity of the motor. Oiling: Maintain oil in wells to the overflow. Starting: Single phase motors are started by first throwing the starting switch down into the starting position, and when the motor is up to speed, throwing it up into the running position. Do not hold the switch in starting position over 10 seconds. Starter for single phase motors above ½ H.P. are arranged with an adjusting link at the bottom of the panel. The link is shown in the position of least starting torque and current. Connect from W to 2 or W to 3 for starting heavier loads. Two or three phase motors are started simply by closing the switch. These motors start full load without starters. The motor should start promptly on closing the switch. It should be started the first time without being coupled to the line shaft. If the motor start free, but will not start loaded, it shows either that the load upon the motor is too great, the line voltage too low, or the frequency too high. The voltage and frequency with the motor running should be within 5% of the name plate rating and the voltage with 10 to 15% while starting. If the motor do not start free, either it is getting no current or something is wrong with the motor. In either case an electrician should be consulted. Solution: To reverse the direction of rotation interchange the leads marked "XX" in the diagrams. Temperature: At full load the motor should not heat over 75 degrees Fahr. above the temperature of the surrounding air; if run in a small enclosed space with no ventilation, the temperature will be somewhat higher.

2008 Ques. What should be noted with respect to generator pulleys?

Ans. A pulley of certain size is usually supplied with each generator by its manufacturer, and it is not generally advisable to depart much from the dimensions of this pulley. Accordingly, the solution of the pulley problem usually consists in finding the necessary diameter of the driving pulley relative to that of the pulley on the generator in order to furnish the required speed.

Ques. What is the chief objection to belt drive?

Ans. The large amount of floor space required.

Fig. 2,810.—Tandem drive for economizing floor space with belt transmission. Belts of different lengths are used, as shown, each of which passes over the driving wheel d of the engine, and then over the pulley wheel of one of the generators. In such an arrangement the belts would be run lengthwise through the room in which the machines are placed, and it is obvious that since the width of the room would be governed by the width of the machines thus installed, this method is a very efficient one for accomplishing the end in view.

Ques. How may the amount of space that would ordinarily be required for belt drive, be reduced?

Ans. By driving machines in tandem as in fig. 2,810, or by the double pulley drive as in fig. 2,811. 2009

Ques. What is the objection to the tandem method?

Ans. The most economical distance between centers cannot be employed for all machines.

Ques. What is the objectionable tendency in resorting to floor economy methods with belt transmission?

Ans. The tendency to place the machines too closely together. This is poor economy as it makes the cleaning of the machines a difficult and dangerous task; it is therefore advisable to allow sufficient room for this purpose regardless of the method of belting employed.

Fig. 2,811.—Double pulley drive for economizing floor space with belt transmission. Where a center crank engine is used both pulleys may be employed by belting a machine to each as shown. Although considerable floor space would be saved by the use of this scheme if the generators thus belted were placed at M and G yet still more floor space would be saved by having them occupy the positions indicated at M and S.

Ques. What is the approved location for an alternator exciter?

Ans. To economize floor space the exciter may be placed between the alternator and engine at S in fig. 2,811.

Belts.—In the selection of a belt, the quality of the leather should be first under consideration. The leather must be firm, yet pliable, free from wrinkles on the grain or hair side, and of an even thickness throughout. 2010

Fig. 2,812.—Separately excited belt driven alternator showing approved location of exciter. In an electrical station where alternating current is generated, the alternators for producing the current generally require separate excitation for their field windings; that is, it is usually necessary to install in conjunction with an alternator a small dynamo for supplying current to the alternator field. The exciter is a comparatively small machine; in fact, it requires only about 1 per cent. of the capacity of the alternator which it excites, and so being small is often belted to an auxiliary pulley mounted on the alternator shaft. Considerable floor space would be occupied by an installation of this nature if the exciter be placed at M, and belted to the alternator as indicated by the dotted lines. By locating the exciter at S, between the alternator and the engine, much floor space will be saved and the general appearance of the installation improved.

If the belt be well selected and properly handled, it should do service for twenty years, and even then if the worn part be cut off, the remaining portion may be remade and used again as a narrower and shorter belt.

Besides leather belts, there are those made of rubber which withstand moisture much better than leather belts, and which also possess an excellent grip on the pulley; they are, however, more costly and much less durable under normal conditions.

In addition to leather and rubber belts, there are belts composed of cotton, of a combination of cotton and leather, and of rope. The leather belt, however, is the standard and is to be recommended.

Equally important with the quality of a belt is its size in order to transmit the necessary power.

The average strain under which leather will break has been found by many experiments to be 3,200 pounds per square inch of cross section. A good quality of leather will sustain a somewhat greater strain. In use on the pulleys, belts should not be subjected to a greater strain than one eleventh their tensile strength, or about 290 pounds to the square inch or cross section. This will be about 55 pounds average strain for every inch in width of single belt three-sixteenths inch 2011 thick. The strain allowed for all widths of belting—single, light double, and heavy double—is in direct proportion to the thickness of the belt.

Ques. How much horse power will a belt transmit?

Ans. The capacity of a belt depends on, its width, speed, and thickness. A single belt one inch wide and travelling 1,000 feet per minute will transmit one horse power; a double belt under the same conditions, will transmit two horse power.

Fig. 2,813.—One horse power transmitted by belt to illustrate the rule given above. A pulley is driven by a belt by means of the friction between the surfaces in contact. Let T be the tension on the driving side of the belt, and T', the tension on the loose side; then the driving force = T-T'. In the figure T is taken at 34 lbs. and T' at 1 lb.; hence driving force = 34-1 = 33 lbs. Since the belt is travelling at a velocity of 1,000 feet per minute the power transmitted = 33 lbs. × 1,000 ft. = 33,000 ft. lbs. per minute = 1 horse power.

This corresponds to a working pull of 33 and 66 lbs. per inch of width respectively.

Example.—What width double belt will be required to transmit 50 horse power travelling at a speed of 3,000 feet per minute?

The horse power transmitted by each inch width of double belt travelling at the stated speed is

( 1 × 3,000 / 1,000 ) × 2 = 6,

hence the width of belt required to transmit 50 horse power is

50 ÷ 6 = 8.33, say 8 inches. 2012

Ques. At what velocity should a belt be run?

Ans. At from 3,000 to 5,000 feet per minute.

Ques. How may the greatest amount of power transmitting capacity be obtained from belts?

Ans. By covering the pulleys with leather.

Ques. How should belts be run?

Ans. With the tight side underneath as in fig. 2,814.

Figs. 2,814 and 2,815.—Right and wrong way to run a belt. The tight side should be underneath so as to increase the arc of contact and consequently the adhesion, that is to say, a better grip, is in this way obtained.

Ques. What is a good indication of the capacity of a belt in operation?

Ans. Its appearance after a few days' run.

If the side of the belt coming in contact with the pulley assume a mottled appearance, it is an indication that the capacity of the belt is considerably in excess of the power which it is transmitting, 2013 inasmuch as the spotted portions of the belt do not touch the pulley; and in consequence of this there is liable to be more or less slipping.

Small quantities of a mixture of tallow and fish oil which have previously been melted together in the proportion of two of the former to one of the latter, will, if applied to the belt at frequent intervals, do much toward softening it, and thus by permitting its entire surface to come in contact with the pulley, prevent any tendency toward slipping. The best results are obtained when the smooth side of the belt is used next to the pulley, since tests conducted in the past prove that more power is thus transmitted, and that the belt lasts longer when used in this way.

Fig. 2,816.—The Hill friction clutch pulley for power control. The clutch mechanism will start a load equivalent to the double belt capacity of the pulley to which the clutch is attached.

Ques. What is the comparison between the so called endless belts and laced belts?

Ans. With an endless belt there is no uneven or noisy action as with laced belts, when the laced joint passes over the pulleys, and the former is free from the liability of breakage at the joint.

Ques. How should a belt be placed on the pulleys?

Ans. The belt should first be placed on the pulley at rest, and then run on the other pulley while the latter is in motion. 2014

The best results are obtained, and the strain on the belt is less, when the speed at which the moving pulley revolves is comparatively low. With heavy belts, particular care should be taken to prevent any portion of the clothing being caught either by the moving belt or pulleys, as many serious accidents have resulted in the past from carelessness in regard to this important detail. The person handling the belt should, therefore, be sure of a firm footing, and when it is impossible to secure this, it is advisable to stop the engine and fit the belt around the engine pulley as well as possible by the aid of a rope looped around the belt.

Fig. 2,817—Sectional view of Hill clutch mechanism. In every case the mechanism hub A, and in a clutch coupling the ring W, is permanently and rigidly secured to the shaft and need not be disturbed when removing the wearing parts. When erected, the adjustment should be verified, and always with the clutch and ring engaged and at rest. If the jaws do not press equally on the ring, or if the pressure required on the cone be abnormal, loosen the upper adjusting nuts T´ on eye bolts and set up the lower adjusting nuts T´´ until each set of jaws is under the same pressure. Should the clutch then slip when started it is evident that the jaw pressure is insufficient and a further adjustment will be necessary. All clutches are equipped throughout with split lock washers. Vibration or shock will not loosen the nuts if properly set up. The jaws can be removed parallel to the shaft as follows: Remove the gibs V, and withdraw the jaw pins P, then pull out the levers D. Do not disturb the eye bolt nuts T´ and T´´. The outside jaws B can now be taken out. Remove the bolt nuts I allowing the fulcrum plates R to be taken off. On the separable hub pattern the clamping bolts must be taken out before fulcrum plate is removed. The inside jaws C may now be withdrawn. Always set the clutch operating lever in the position as shown in fig. 2,816 to avoid interference with mechanism parts. Oil the moving parts of the clutch. Keep it clean. Examine at regular intervals.

Ques. Under what conditions does a belt drive give the best results?

Ans. When the two pulleys are at the same level.

If the belt must occupy an inclined position it should not form a greater angle than 45 degrees with the horizontal.

Ques. What is a characteristic feature in the operation of belts, and why?

Ans. Belts in motion will always run to the highest side of a 2015 pulley; this is due partially to the greater speed in feet per minute developed at that point owing to the greater circumference of the pulley, and also to the effects of centrifugal force.

If, therefore, the highest sides of both pulleys be in line with each other, and the shafts of the respective pulleys be parallel to each other, there will be no tendency for the belt to leave the pulleys when once in its proper position. In order that these conditions be maintained, the belt should be no more than tight enough to prevent slipping, and the distance between the centers of the pulleys should be approximately 3.5 times the diameter of the larger one.

Fig. 2,818.—Hill clutch mechanism Smith type. The friction surfaces are wood to iron, the wood shoes being made from maple. All parts of the toggle gear are of steel and forgings with the exception of the connection lever which is of cast iron.

Ques. What minor appurtenances should be provided in a station?

Ans. Apparatus should be installed as a prevention against accidents, such as fire, and protection of attendants from danger.

In every electrical station there should be a pump, pipes and hose; the pump may be either directly connected to a small electric motor or belted to a countershaft, while the pipes and hose should be so placed that no water can accidentally reach the generators and 2016 electrical circuits. A number of fire bucket filled with water should be placed on brackets around the station, and with these there should be an equal number of bucket containing dry sand, the water being used for extinguishing fire occurring at a distance from the machines and conductors, and the sand for extinguishing fire in current carrying circuits where water would cause more harm than benefit. To prevent the sand being blown about the station, each sand bucket, when not in use, should be provided with a cover.

Neat cans and boxes should be mounted in convenient places for greasy rags, waste, nuts, screws, etc., which are used continually and which therefore cannot be kept in the storeroom.

While it is important to guard against fire in the station, it is equally necessary to provide for personal safety. All passages and dark pits should therefore be thoroughly lighted both day and night, and obstacles of any nature that are not absolutely necessary in the operation of the station, should be removed. Moving belts, and especially those passing through the floor, should be enclosed in iron railings. If high voltages be generated, it is well to place a railing about the switchboard to prevent accidental contact with current carrying circuits, and in such cases it is also advisable to construct an insulated platform on the floor in front of the switchboard.

Fig. 2,819.—Method of joining adjacent switchboard panels.

Switchboards.—The plan of switchboard wiring for alternating 2017 current work depends upon the system in use and this latter may be either of the single phase, two phase, three phase, or monocyclic types. The general principles in all these cases, however, are practically identical.

Fig. 2,820 shows the switchboard wiring for a single phase alternator. As an aid in reading the diagram, the conductors carrying alternating current are represented by solid lines, and those carrying direct current, by dotted lines.

Fig. 2,820.—Switchboard wiring for a single phase separately excited alternator. The direct current circuits are represented by dotted lines, and the alternating current circuit, by solid lines.

The exciter shown at the right is a shunt wound machine. By means of the exciter rheostat, the voltage for exciting the field winding of the alternator is varied; this, in turn, varies the voltage developed in the alternator since the main leads of the exciter are connected through a double pole switch G to the field winding of the alternator. 2018