The standard manual of dynamos and practical application of dynamo-electric machinery

Preface

Our aim in bringing out this little book has been to reach a class of readers who, realizing the need of a general fundamental understanding of the application of Electricity, will read with some benefit, we trust, a few descriptions of the modus operandi of the most generallyused class of Electrical Machinery.

It has not been our intention to take up the subjects treated on, in any but the most simple and as we believe, the most easily understood way.

It is becoming more necessary each year for the well qualified steam engineer to be somewhat familiar with Dynamo Electric Machinery in order to advance in his calling. A partial understanding at least is now or soon will be almost a necessity for those engaged in nearly all branches of engineering work. There is hardly a profession which electricity in some way has not entered. The vast majority of the men in charge of our practical work have never had the advantage of a technical education and are therefore unable to follow the advances that are so rapidly being made.

The volt, ampere, and ohm and their relations to each other are the first stumbling blocks and the cause is easily seen by inspecting a few books for definitions of these words.

We have endeavored to impress as much as possible, the formula expressing Ohms Law,

E

R

on which all calculations necessarily take their start. A

6 PREFACE.

thorough understanding of the relations of the volt, ampere and ohm to each other, is without doubt the foundation of all electrical knowledge.

We have also endeavored to keep up to the times and believe we give some interesting descriptions of modem electrical apparatus, which will be of value to those whose main source of light on electrical matters come from catalogues and newspapers.

The dynamo tender, unless partially conversant with the principles on which his machinery operates, will often be perplexed at even the most trivial troubles to which a dynamo is subject. A motorman on our usual electric street cars, could often lessen motor repairs to a great extent by obtaining even an elementary understanding of the motors' action. An understanding of the proper distribution and installation of electric wires would be the means of averting many thousands of dollars loss each year by fire from electrical causes.

There are many good books on the various branches of electrical work but they are too often of such a technical nature as to bar the uneducated reader from obtaining much benefit from them. We hope that a close study of the following pages will place the average beginner on such a foundation as to make the other more complete electrical books more easily understood.

CarIv K. MacFadden.

ElyKMENTARY DATA.

Chapter I

ei.kme:ntary data.

What is electricity? A question often asked and probably never as yet clearly answered.

Those interested in the practical field, find it almost impossible to keep up to the times, in regard to the laws that govern its generation and control. We know that by means of certain combinations of coils of wire and magnets or by means of chemical action, we can produce, we may say, electricity.

We must be content if we master a few leading laws governing the generation and application of the Electric current. Let the Scientists and Philosophers discuss the question as to what electricity is. In dealing with the simple electric current that is generated by dynamos, batteries, etc. , we will find that there are several broad and easily understood laws that govern its practical applications. These laws hold good in all cases and under all conditions, and should be thoroughly understood by anyone desiring to learn even the first and most simple effects of a flow of electric current.

Probably the easiest way to understand this law will be to take a simple case of a pump connected to a loop of water pipe. The pipe is filled with water and it is evident that if the pump is started there will be a circulation of water from the pump through the pipe and back into

KI^KMENTARY DATA.

the pump again. The pump furnishes the power to move the water in the pipe — and it is evident that the water moves through the pipe owing to the pressure exerted by the pump on the water. In (figure i) an open tank, (d) is shown into which the water flows from the pipe. The pump takes the water from the tank to keep the pipe filled, and the speed of the water through the

FIGURE I. — PUMP FORCING V7ATER THROUGH PIPES.

pipe and therefore the quantity of water passing through the pump and pipe in a minute of time, will depend on the pressure given the water by the pump.

If we double the pressure of the water and the friction or resistance to the flow of water in the pipe remains constant, the quantity of water handled by the pump will be doubled. In other words by increasing the pressure, w^e increase the quantity of water passing through the pipe at exactly the same ratio. Now if we found that a guage placed at (a) would have to register 50 lbs. pressure to make 100 gallons of water pass through the pipe in a minute, it is evident that if the friction in the pipe remained the same, that 100 lbs. pressure ought to put 200 gallons through the pipe. It is also evident that

EI/EMKNl'ARY DATA. 9

if icx) feet of pipe a certain size oflFers a definite amount of friction, that twice the length of pipe would have two times the friction or resistance to the flow of water that the loo feet has. Thus to put loo gallons of water a minute through a pipe will take yi the pressure required to force 200 gallons through the pipe. This example may serve the purpose of illustrating the principle of the flow of current from a source of electricity. We will let the dynamo take the place of the pump, which will generate the pressure to send the electricity through the circuit which may consist of lamps, etc., connected by means of conducting wires. The friction in the pipe is represented by the ''resistance" of the wire and circuit, and the amount of water used, represent the quantity of the current of electricity.

Instead of using the pound as the unit of water pressure we will use the term ' 'volt' ' which is the unit of electrical pressure. We also have a term which denotes the unit of ' 'resistance, which is the equivalent of ' 'friction" used in the illustration ot the pump and pipe. The unit of resistance is called the "ohm."

Then lastly the quantity of current in electricity is measured by the unit of current quantity, the "ampere. ' ' This is the quantity of current that a pressure of one volt will force through a resistance of i ohm.

The resistance of a conductor of electricity varies not only with its size or cross section but also with the material of which it is made. Silver, when pure, is the best conductor of electricity known, but copper, when pure, nearly approaches silver and is so much cheaper that it is used in nearly all cases to distribute current for practical purposes.

ro EI^HMKNTARY DATA.

The metals in their order for conductivity are as follows: Silver, Copper, Gold, Aluminum, Zinc, Platinum, Iron, Lead, German Silver, Platinum Silver alloy and Mercury.

In practice the wires or conductors to carry current are either designated in size by their diameter in thousandths of an inch (or mils) or by the sectional area or cross section of the wire expressed in circular mils or by the size in number, as measured by the Standard American or Brown & Sharp Wire Guage.

A circular mil is a circle ^q^qq inch in diameter.

As in the case of pump, the higher the pressure in volts at the dynamo, the larger quantity of electricity (expressed in amperes) will be put through a circuit which has a resistance (expressed in ohms) to the flow of current.

Thus if I volt pressure will force i ampere of current through a circuit having i ohm of resistance, it will take 5 volts to force 5 amperes thiough this same i ohm of resistance and if this resistance is increased to 2 ohms, the pressure would have to be 10 volts to force 5 amperes of current through it.

It will be seen that these terms are dependent on each other and their relation to each other is expressed by what is known as Ohms Law which is expressed:

Current Pressure in Volts E

in = ^ or C = —

Amperes Resistance in Ohms R

**C" standing for current, "K" for electro-motive force or volts, and ''R" for resistance expressed in *'Ohms.'* This relation C=B/R must be remembered for it is the fundamental law of the governing of electric currents, and is used as a foundation to obtain all of the more com-

EI.KMENTARY DATA. II

plex formulas known to the Electrical Engineers.

Take the simple case of a certain make of incandescent lamp, the resistance of the lamp in question is found to be 200 ohms The pressure of the circuit on which this lamp is designed to run is 100 volts, and according to Ohms law the current in amperes which 100 volts pressure will force through 200 ohms of resistance is ^gg or yi which is the number of amperes such a lamp would allow to pass through it if current at 100 volts pressure was applied.

It will thus be seen that it is a very easy matter to obtain any one of these quantities, provided we have the other two given, by a simple multiplying or dividing of the two known quantities. The relations to each other are expressed

E E

C= — , E=R X C, and R= — .

R C

There is still another term with which the practical man is brought in contact and that is the unit of power, the *'watt." This watt is the /(^ze'^r represented by the passing of i ampere of current through i ohm of resistance and can always be obtained of any current by multiplying the number of volts by the number of amperes.

Thus in the incandescent lamp before spoken of, the watts used by the lamp would be 100 (volts) x^ (^inp) = 50 (the number of watts), this being the amount of electrical energy necessary to be applied continually to keep the lamp burning. Such an incandescent lamp would be termed "a 50 watt incandescent lamp." An arc lamp which needed a current of 10 amperes at a pressure of 50 volts to keep it in operation would be termed a * '500 watt arc lamp".

ELEMENTARY DATA.

There are two entirely diflferent methods of distributing current to lamps etc., connected to dynamos.

The plan illustrated by means of the pump in (figure i) may be seen as applied to a dynamo and lamps in (figure 2) (a), in which the dynamo D supplies current for lamps L, and is known as the Series System. It will be seen in plan (a) that the lamps are connected in "series" that is, the current which passes out from the positive (-|-) D D D

Series (a) Multiple or Parallel (b) Mulliple Series {c) FIGURE 2. — SYSTEMS OF CURRENT DISTRIBUTIOIT.

brush of the dynamo must go through the whole series of lamps before the negative ( — ) brush is reached, the number of amperes flowing through the v/ire will be found to be the same at whatever point it is measured, but the pressure in volts will vary with the number of lamps through which current is forced. If each of the lamps required lo amperes of current to bring it up to candle power, and it took 50 volts pressure to put 10 amperes of currei • ^Wough it, or in other words, if the lamp had 5

ELEMENTARY DATA. I3

ohms resistance, then the dynamo would have to generate 50 volts for every lamp in the series of lamps or on a 10 lamp circuit the voltage would be 500, 20 lamps 1000 volts and so on. Such a system of lighting is used in operating the usual type of * 'Series arc lamps." The current in amperes remains nearly constant, but the voltage at the dynamo varies with the number of lamps through which it has to force current.

Plan (b), figure 2 shows the Multiple System or the system of placing lamps in parallel or multiple arc. The dynamo (D) furnishes current of a uniform pressure to lamps (L) connected to the mains marked (-[-) and ( — )the current from the dynamo however varies as to its quantity in amperes, on the number of paths through the lamps from the positive to the negative mains. This plan of current distribution is used in furnishing current to the usual incandescent lamps, or in any other work requiring a uniform pressure or voltage. It will thus be seen that the multiple system is the opposite from the series system in several ways. In the series system the larger the number of lamps the higher the pressure in volts, although the current in amperes remains constant, while in the multiple system the voltage remains practically uniform and the amperes given out by the dynamo varies with the number of lamps connected between the mains.

The Multiple-Series plan of distribution is a combination of both the previous methods and is shown in plan (c) figure 2. This system of wiring is used to operate arc lamps on incandescent or constant potential circuits and in the other special places which will be spoken of later on in Chapter IV.

14 KI.EMKNTARY DATA.

746 watts are equal to i electrical horse power and by dividing the output of a dynamo in watts by 746 we can obtain the output of the dynamo in electrical horsepower or E. H. P.

1000 watts = I kilo watt and is a term generally used to give the rating of generators or dynamos. The abbreviation K. W., is used to express kilo-watt. It is evident that the term kilo- watt as used to describe a dynamo does not denote the voltage, or the current in amperes, which the dynamo may be designed to generate. It simply means, for example, in a i kilo watt generator, that the generator has a capacity of supplying 1000 watts of electricity, which may be represented by i ampere at 1000 volts pressure, 1000 amperes at i volt, 10 amperes at 100 volts, 100 amperes at 10 volts or any other combination of current that equals 1000 watts, as the case may be.

A proper description of such a generator would be, for instance, a i kilo watt, 100 volt generator, which of course lets us know that such a dynamo will generate 10 amperes at the 100 volt pressure, thus making one thousand watts or one kilo-watt. Hence Watts or W. =C x E the product of amperes and volts.

The instruments used for measuring electrical pressure in volts are generally called voltmeters, or pressure indicators. Those for measuring amperes or quantity are called ammeters.

The resistance in ohms is measured usually by means of an instrument called the Wheatstone bridge, or rarely an ohmmeter.

Wattmeters are used for measuring watts, or the product of volts and amperes.

MAGNETISM AND INDUCTION. I5

Chapter II. Magnetism And Induction

Inasmuch as the generation of dynamo electricity is effected by means of the action of magnetism, it is well to take up the subject of magnets first.

A magnet, as known to practice, is a piece of iron or steel, which has the power of attracting other pieces of iron to it. There are two types of magnets, permanent magnets, and electro-magnets. A permanent magnet is usually made of hard tempered steel, which after having been brought under the influence of some magnetizing apparatus, retains a more or less amount of magnetism. We often see them in horse-shoe form, known as horse-shoe magnets. Large permanent magnets, however, are expensive to make, and are extremely weak in comparison to their weight, and in addition they seldom hold their magnetism for any length of time.

The other type, known as the electro-magnet, is quite a diflferent thing. If a piece of iron has wound around it, a few turns of insulated wire, and a current of electricity be passed through the wire, the iron immediately will be magnetized, and will remaij. magnetized as long as the current passes through tW wire. The moment, however, the current through 1 le wire is stopped the iron is no longer magnetized. Tl as l6 MAGNETISM AND INDUCTION.

it is seen that the current in passing around the iron has an efifect on it, and magnetizes it.

The amount of magnetism shown by the iron centre of the coil will depend on two factors, the number of turns of wire around the core of iron, and the number of amperes of current passing around through the turns. Thus with lo amperes passing around the core, 20 turns of wire will have twice the magnetizing power that 10 turns will have. . The effect will depend on what is known as the number of ' 'ampere turns' ' in the coil of wire, the ampere turns being the product of the number amperes and turns, thus, if we have 10 turns and 10 amperes passing through them, we have a coil of 100 ampere turns, which will have J4 the effect that 200 ampere turns will have. It is evident, that 100 turns with one ampere passing through them, will have the same effect as 50 amperes and 2 turns, or 100 amperes and one turn, each of the above quantities being equal to . "X) ampere turns.

We have practically no limit as to the strength of the magnet we may construct. The very powerful magnets used in dynamos lately constructed, are made by winding an immense number of turns on large iron cores, and then sending currents of electricity through them, thus making a large number of ampere turns, and producing an immense magnetic effect.

Iron has been spoken of as the cores for the magnets because it is the metal found to be capable of carrying more magnetism than any other. In any coil of wire carrying an electric current we may imagine a large number ''lines of magnetism" being generated by the current, each line starting from the end of the magnet

called the positive end and taking a path through the air or some magnetic material back to the other end of the coil called the negative end. These little loops are thrown out from the end of the coil and will follow the easiest path back to the other end, thus completing a magnetic circuit. A permanent magnet made of hardened steel throws out these same little loops from its poles without being excited by means of the passage of a current of electricity arou-nd it.

FIGURE 3. — KlvKCTRO-MAGNET AND ARMATURE SHOW- ING WNES OF MAGNETISM.

If a piece of iron or steel is placed in such a position with relation to the coil as to be in the magnetic influence or * Afield," a large number of these lines of magnetism will take the path through the iron in preference to that through the air owing to the fact that iron will l8 MAGNETISM AND INDUCTION.

carry lines of magnetism better than air or any other material. The iron under these conditions will tend to assume the position in which the largest number of the lines of force or magnetism will pass through it, and for this reason iron is * 'attracted" to the coil or magnet. Some iron carries these lines thousands of times better than air. Figure (3) shows the action on a horse-shoe magnet made of soft iron, having a coil of wire on each limb.

The nearer the armature or * 'keeper" of the horse-shoe magnet approaches the ends of the magnet, the stronger will be the pull, owing to the increased number of lines of magnetism it carries. A compass needle points north and south because in that position the metal of the compass is parallel to and is carrying more of the lines of the Earth's magnetism through it, than at any other position.

If a coil of wire is wound on a hollow spool of wood or other non-magnetic material, and- a current of electricity be passed through the coil, it will be found that a piece of iron will be drawn up into the coil of wire and tend to assume a central position in the coil. On stopping the flow of current through the coil, the iron core will no longer be attracted. When the core of the coil or *'selonoid" as it is called, is in its centre, it is carrying the maximum number of lines of magnetism.

The selonoid is a form of magnet often used in the manufacture of arc lamps, etc. , and is adapted for this purpose on account of the large movement of the core compared to that of the armature, or keeper of the usual type of electro-magnet with an iron centre.

There is still another wonderful effect of magnetism, that of induction. If a magnet be moved about in the

MAGNETISM AND INDUCTION. I^

vicinity of a coil of wire whose ends are connected to a means for measuring the passage of an electric current, it will be found that a current of electricity will be generated in the wire of the coil, and that it flows only when the magnet is being moved near the coil. Also, that as the magnet moves toward the coil» that the current flows in one direction through the coil, and as it is being pulled away, the current flows in an opposite direction.

By arranging a suitable set of coils and magnets, in such manner that the coils pass in front of the magnets, we may be able to generate strong currents of electricity, and in fact, all dynamos and generators are operated on this plan. The usual method employed ib to so mount an electro magnet, called the field magnet, that there is a break in the iron magnetic circuit, across which the lines of magnetism will pass in completing their circuit. In this gap in the magnetic circuit, an armature consisting of a number of coils of insulated wire mounted on a shaft, is revolved by means of power applied to it. As these coils of insulated wire move through the lines of magnetism, currents of electricity are generated in them which are carried away from the armature, to the lamp, etc., to which the dynamo is connected.

Chapter III. Theory Of^ Dynamos

An electric generator or dynamo is a combination of coils of wire and magnets, which have a movement with relation to each other and which, when supplied with suitable mechanical power will generate currents of electricity.

In practice, they consist without exception of an armature in which the currents of electricity are generated, and a field magnet or magnets which furnish the lines of magnetism, through which the coils of wire on the armature pass, and thus generate current.

The armature may be, and usually is, the moving part; but this is not by any means a necessary thing, for the field magnets may be made the moving part with the armature stationary and accomplish the same result. At present the stationary armature is found only on a few types of dynamos which are usually used for generating alternating currents. It has been shown that the movement of a coil of wire with its ends connected, in the vicinity or magnetic field of a stationary magnet, will generate currents of electricity in the coil. If the coil of wire approaches the magnet, the flow of current will be in one direction, and if it is drawn away, the current will flow in an opposite direction through the coil. If the coil is held stationary near the mag-

THEORY OE DYNAMOS.

net, no current will be generated in it. This is all caused by the coil of wire passing through, or * 'cutting'*, the lines of magnetism. The current generated, depends however, on several factors. In the first place let us construct, for illustration, the simplest possible form of a dynamo. To furnish the lines of magnetism, we will use a simple steel horse-shoe shaped permanent magnet, M, see figure 4.

I«'IGUR:e 4.— SINGI.K I^OOP ARMATURK WITH COLLECTOR

RINGS, REVOLVING BETWEEN POLES OF

PERMANENT MAGNET.

On a shaft we mount a coil of wire consisting of one convolution, the ends of which are connected to insulated rings mounted at one end of the shaft and on which two brushes bear, and thus connect the coil of wire to a suitable measuring instrument (a) . In the diagram we will assume that the lines of magnetism are being concentrated between the ])oles N end S; N being the north and S the south. Thus if the coil of wire on the armature is revolved on its shaft, it is evident that with the coil in the position shown, will have Its right hand half moving down before the pole S, and the left hand half moving upward before the pole N, and since we assume that there are an immense number of lines of magnetism flowing through the space from N to S, it is evident that the moving coil must *'cuf these lines, and it is this action that generates current, or to be more correct, generates electrical pressure which expends itself in creating a flow of current, the amount depending on the resistance of the circuit. Assuming that the lines of magnetism from the permanent field magnets, remains constant, we will find that the electrical pressure generated, and thus the current will depend on simply the rate at which these lines of magnetism are cut, if at looo revolutions per minute the coil of a single turn will generate 5 volt pressure, 2000 revolutions per minute will generate 10 volts pressure. The direction in which the current will flow, will depend on the direction of movement of the conductor through the lines of magnetism.

In a simple loop, whose ends are connected to rings, mounted on shaft as shown in figure 4, the current through half a revolution will flow through the coil in one direction, and in the remaining half revolution the current will flow in an opposite direction. Thus in a

THEORY O^ DYNAMOS.

complete revolution, the current will flow first in one direction, and then reverse and flow in an opposite direction, and in this way produces what is known as an alternating current. This alternating type of current can only be used for certain kinds of work, and to so arrange ths connections that all the impulses or waves of current generated in the armature will be given out in one direction, a commutator is necessary. The action of the com-

C-

FIGURE 5. — SINGlvE lyOOP ARMATURE ON IRON CORE WITH COMMUTATOR AND BRUSHES.

mutator may be understood from study of figure 5, which shows the same loop x>f wire between the poles of a magnet, as v/as shown in figure 4, with the exception that instead of rings mounted in the shaft, with brushes

THEORY 01^ DYNAMOS.

bearing on them a split ring is shown, each half of whicV is connected to a terminal of the single armature coil of one turn (c). The two half rings are insulated from each other and from the armature shaft, and the action may be described as follows: — From the point (A) figure 5 to the point (B) which is yi revolution, the current flows in such a direction as to make the brush (-]-) a positive brush, that is, the current flows from -|- to — ,

FIGURE 6. — ALTERNATING CURRENT WAVE.

the current generated depending on the rate at which lines of magnetism are being cut by the loop of wire. The current with the loop at the line ( A-B ) will be zero, for this is the point at which the current is reversing its direction in the loop, owing to the fact that

THEORY Olf DYNAMOS. 25

the direction in which the loop cuts the lines of magnetism is being changed. From this position on dotted line A — B, the current will gradually rise to a tnaximum when the loop is on the line C — D, which is the point at which a certain given movement of the loop will cut the greatest number of lines of force. The rise and fall oi current in an alternating current circuit may be shown readily by the cut in figure 6. The line A — B representing the zero line or line of no flow of current in the coil. The distance from i to 2 represents one complete revolution and the curved line C represents the current produced by the revolving loop. The portion of the curved line above the zero line represents current flowing in a positive direction and the portion below the line will represent the negative flow of current. The total curve from i to 2, represents one complete alternation, which in the combination shown in figure 4, means one revolution. If we had the coil making 2000 revolutions per minute, there would be 2000 of such waves as shown in curve i — 2. With a commutator such as shown in figure 5, and with the brushes placed as shown, it will be seen that just as the current in the coil is at zero the commutator has moved in such a position that the brushes are just changing from one segment of the commutator to the other, thus keeping the rising side of the loop connected to the negative brush and the downward moving side of the loop connected to the positive brush. In this way we can send all the impulses or waves of current from the revolving coil on the circuit in one direction, thus producing a pulsating current, but at the same time one whose flow is always in one direction, The current curve of such a dynamo will now be