THE DYNAMO, OR GENERATOR.

The word dynamo, meaning power, is one transferred from the Greek to the English language, hence the primary meaning of the term signifying the electric generator is, the electric power machine.

The word generator is derived from a word meaning birth giving, hence also the dynamo is the machine generating or giving birth to electricity.

Fig. 217.—See page 251.

Again, the dynamo is a machine driven by power, generally steam or water power, andconverting the mechanical energy expended in driving it, into electrical energy of the current form.

To summarize, the dynamo-electric generator or the dynamo-electric machine, proper, consists of five principal parts, viz:

1.The armature or revolving portion.

2.The field magnets, which produce the magnetic field in which the armature turns.

3.The pole-pieces.

4.The commutator or collector.

5.The collecting-brushesthat rest on the commutator cylinder and take off the current of electricity generated by the machine.

Fig. 218 shows a dynamo of the early Edison type—the names of the principal parts are given in the note below, as well as those of the other parts of the machine.

Fig. 218.

This is a two-pole machine, direct current; the figure is introduced to show the “parts” only—as this dynamo has been largely superseded by others of the four pole type.

Note.—A, Magnet yoke; B, Magnet and field piece; C, Pole piece; D, Zinc field piece; E, Armature; F, Commutator; I, Quadrant; JJ, Brushes; K, Adjusting handle for the brushes; L, Switch pivot; M, Pilot lamp receptacle; N, Negative lug; O, Switch lever; P, Positive lug; Q, Positive terminal; R, Negative terminal; S, Negative rod; T, Pole piece; UU, Bearings; X, Slides for belt tightener; VVV, Driving pulley; Y, Connecting blocks, one on each side of machine.

An electric motoris a machine for converting electrical energy into mechanical energy; in other words it produces mechanical power when supplied with an electric current; a certain amount of energy must be expended in driving it; theintakeof the machine is the term used in defining the energy expended in driving it; the amount of power it delivers to the machinery is denominatedits out-put.

The difference between the out-put to the intake is the realefficiencyof the machine; it is well known that the total efficiency ofan electric distribution system, which may include several machines, usually ranges from 75 to 80 per cent., at full load, and should not under ordinary circumstances fall off more than say 5 per cent. at one-third to half load; the efficiency of motors varies with their size, while a one horse-power motor will, perhaps, have an efficiency of 60 per cent., a 100 horse-power may easily have an efficiency of 90 per cent. and the larger sizes even more.

The general and growing application of electric power to the driving of all kinds of machinery including pumps makesthe question of motor driving one of the most important in the power field. For many purposes, a single speed is sufficient, but for others, it is imperative that the speed should be variable; and for still others, though not absolutely necessary, a speed adjustment is very desirable.

While thedirect-current motorhas been in this field so long that its properties are well known and its possibilities fully developed, in the operation of motors located in the immediate neighborhood of the generator thealternating-current motorhas marked advantages where a large area of territory has to be covered and the conditions are nearly uniform, that is to say—

Where the current has to be transmitted a long distance and the load is approximately constant, the alternating system is preferred, as it can be operated with small main lines or conductors. This effects a saving in copper, over the direct system which requires larger conductors.

Fig. 219.

Fig. 220.

Fig. 217, on page 247, showsa four-pole generatordesigned to run by a belt or directly connected to an engine. The five parts named, as the principal parts of a dynamo, are all shown in the figure. The machine is arranged ready to be bolted to the floor.

Fig. 219on the opposite page is thearmaturewhich is made up of coils of insulated wire, the free ends of which,see Fig. 220, are united to the arms of thecommutator bars. When the armature is finished, as shown, the wire forms an unbroken circuit.

Fig. 221.

Fig. 221is intended to represent another form of armature, but the principle upon which it operates, is the same, as the other shown. A A, represents the wire coils of the armature, B, is the shaft with its journals, C, is the commutator. All commutators both for generators and for motor armatures are insulated by mica between the bars.

Fig. 222.

Fig. 222showsa woven wire brush. The brushes on the dynamo,page 247, are made of carbon.

Fig. 223.

Fig. 223shows an alternatinginductionmotor. Induction is a property by virtue of which an electric current is transferred from one conducting line to anotherwithout any metallic connection; it is that influence by which astrong currentflowing through a conductor controls or affectsa weaker currentflowing through another conductor in its immediate neighborhood,—the strong current remaining unaffected.

Fig. 224.

Fig. 224exhibits the armature for the above alternator; itis familiarly called a “squirrel cage armature” on account of its resemblance to the wheel in a squirrel’s cage.

Its peculiar construction enables it to run without producing any sparks; this feature renders it safe to run where there are explosive gases which might be ignited by an electric spark. In the machine the bearings are cast solid with the end shields, thus assuring perfect alignment when properly turned. Another feature is the automatic self adjusting bearings which are lubricated mechanically by rings resting upon the shaft. These rings were formerly a failure, but by the use of mineral oils are now a success.

This machine is one of the simplest designs of alternating motors, the example,Fig. 223, is one developing one hundred horse-power.

Fig. 225.

Fig. 225shows a revolvingfieldwith “spider.” In this construction of generators or motors the field revolves in place of the armatures, the first object of this design is to reduce the high rotative speed; it is also claimed to have a better electrical efficiency.

The field spider consists of an extra heavy cast iron pulley which is keyed to the shaft; the low speed at which it runs permits the employment of bolts to secure the field coils and laminated pole pieces to the rim of the spider, as shown in the engraving. With this construction each individual pole piece can be removed and replaced independent of the others.

The laminated pole piece, one of which is shown in detail inFigs. 226-229, takes its name from the fact that it is built up of a large number of layers of soft sheet iron, which it has been demonstrated give a better electrical efficiency than a solid iron. Soft iron is the most magnetic of all metals and is better suited for pole pieces than steel.

It should be understood that each individual pole piece is insulated from the others as well as from the spider. The pieces of sheet iron are stamped out—like washers and are cut apart and the ends united so as to form a continuous coil, like a coil of wire and each coil is isolated; mica is used between the layers.

Figs. 226-229.

Fig. 230is designed to illustrate the front of a continuous current two wire switchboard with circuit breakers; these are made up usually of marble or slate so that they will not burn; the Insurance Underwriters require a non-combustible material at this place, as well as hangers, and insulators used for conductors.

The Switchesshown in the middle of the board, are enlarged inFig. 232, and are used for closing the connections with the generators and lines running to various parts of the field to be lighted or furnished with power.

The switch handles are made usually of wood or hard rubber; the blades are of copper. The connections are soldered into the sockets shown upon the ends of the screws which project beyond the back of the switch-board.

The upper row of figures as shown inFig. 230and enlarged in the engraving,231, arecircuit-breakers. The use of these is analogous to that of the safety-valve upon a steam boiler, so that when the pressure in the circuit exceeds that at which it is set the “breaker” opens the circuit and thus prevents damage.

Fig. 230.

In this case, the main contact is formed by means of a laminated brush while the final stroke is made on carbon, the motion of this breaker is by means of a toggle-joint which so multiplies the power applied that it does not require much of an effort to close it; this device maintains the same speed in operating the breakers when the circuit-breaker is tripped.

A Rheostatis a device for controlling the amount of electricity in a conductor—by the insertion of coils of wire in a box—which may be successively switched in or out of the main circuit by means of a lever and button-switch. The best place to install a rheostat is on a wall or post, as the resistance transforms a portion of the electric energy into heat, which heat must be dispersed into the atmosphere.

A transformeris an induction coil employed usually for lowering electric pressure, but it may also be used for raising the same, in which case it is sometimes called abooster.A compensatoris a transformer which works automatically.

Fig. 231.

Fig. 232.

Ammetersrecordthe quantity of current flowing through the circuit, in amperes.Voltmetersrecordthe pressureor strength of the current involts.

AnAmpereis an electric current which would pass through a circuit whose resistance is one ohm under an electro-motive force of one volt. AVoltis an electro-motive force of sufficient strength to causea current of one ampere to flow against a resistance of one ohm.

Theampereis the unit for calculations relating tothe quantityor volume of a current; thevoltis the unit for calculating thepressureor strength of the current.

The action of the electric currentin producing rotation in an electric motor is really quite simple. While many electrical problems are comparatively complicated, the principal elements in the operation of electric motors may be readily understood. The fundamental fact in this connection is the relation between an electric current and a magnet.

If a piece of round bar iron be surrounded by a coil through which an electric current passes, it becomes a magnet. InFig. 233the passage of a current through the coil of wire around the iron bar in either direction,renders the iron a magnet, with all its well-known properties. It will attract iron, and the space surrounding it becomes magnetic. Iron filings will arrange themselves in the direction shown by the dotted lines in the figure. One end of the magnet is the North or positive + pole and the other the South or negative - pole.

If a wire, such asCD, be moved past either pole of the magnet, there will be a tendency for current to flow in the wire either fromCtoDorDtoC, according to the character of the pole past which it is moved, and to the direction of the movement. If the ends of the wireCDare joined by a conductor, so that there is a complete circuit, a current of electricity will flow through this circuit.

This circuit may be a simple wire, as shown by the lineCEFD, or it may be the wire coils on machines enabling the current to produce mechanical work, or it may be electric lamps producing light. The indispensable feature is that there shall be a complete unbroken circuit fromCtoDfor the current to flow, no matter how complicated or how long this circuit may be.

This description of a dynamo and motor carries with it all of the elementary theory of electric generators and motors that is necessary for an attendant to know in order to take reasonably intelligent care of electric machines. Further useful knowledge must be acquired by studying the different types of electric motors and dynamos. All these other types ofdirect currentmachines have the same elementary theory, although their construction may be quite different.

By suitable illustrations the operation of the electric motor as applied to pumps will be easily understood; its application to other machines is the same in theory and practice.

“Why an electric motor revolves” is a question well worth careful, and, if necessary, long study.

Fig. 233.

The reason why there is a tendency for an electric current to flow in the wireCDwhen it is moved in the vicinity of a magnet is not fully known. There are several theories, all more or less complicated, and depending upon pure assumptions as to the nature of an electric current. For practical purposes it matters little what the reason is,the fact that current flows when there ts an electric pressure in a closed circuit, is the important thing, and it serves all useful purposes to know that current does flow, and that its direction and amount are always the same under similar circumstances. There are many facts in mechanics that are accepted and used practically, about which little is known as to their fundamental and primary causes, and this fact about motors and dynamos is, therefore, only one of many which all must accept without a full and complete explanation.

The intensity of the electric pressure, or electro-motive force, depends upon the velocity of revolution of the wire sections in the armature and upon the strength of the magnets, and the quantity of current depends upon the electro-motive force and upon the amount of the resistance in the circuit. Other things being equal, the current, flowing through a long small wire, or greater resistance, will be less than through a short, thick wire, or a less resistance.

Having seen that when a wire is moved in the vicinity of a magnet an electric pressure is produced which will cause a current to flow in a closed circuit, one can easily conceive of many ways in which, by combining magnets and wires so that there will be a relative motion between them, a current of electricity may be generated. In order to cause a continuous flow the relative motion must be continuous; and if the current is to be uniform the motion must be uniform.

Fig. 234.

Two electro-magnets are shown inFig. 234, in which the North pole of one magnet is near the South pole of the other, and the magnetic field between the two lies in the approximately straight lines between the two magnets, as indicated by the dotted lines. If the wireCDbe moved across this field and its ends be joined, as by the metallic circuitCEFD, a current will flow in this circuit. The wireCDmay be made to revolve around the wireEF, passing in front of one pole and then in front of the other pole, as inFig. 235. The current in the circuit will pass in one direction when the wire is passing one pole, and in the other direction when it is passing the otherpole. The connection between this elementary arrangement and the dynamo is easily recognized. In the dynamo a magnetic field is produced by electric magnets, called “pole pieces,” and a considerable number of wires similar to the wireCDare placed upon an armature so that they revolve in front of these poles. Each individual wire produces current first in one direction and then in another direction, as explained above; but if there be many wires there will always be the same number in front of the North, or positive pole, and the same number in front of the South, or negative pole, so that the total or resultant action is practically uniform, and may be made to produce a continuous current. Such a machine is the common direct current dynamo, or motor.

Fig. 235.

A dynamo transforms mechanical into electrical energy, and a motor transforms electrical into mechanical energy. The two operations are reversible, and may be effected in the same machine; a dynamo may be used as a motor, or a motor may become a dynamo.

A dynamo is a motor when it is driven by a current of electricity, and it is a dynamo when it is driven by mechanical power and produces an electric current.If a motor be driven by an engine, it can deliver a current of electricity which is able to operate other motors or electrical apparatus or lights. A simple form of electric machine is shown inFig. 236, which is a general form of the electric motor. In this there are two projections of steel,HandG, which are made electro-magnets by the current flowing through the wires wound aroundthem from any source of electricity, such as a battery atIandJ. These magnets have poles facing toward an armature,K, on a shaft. The polesGandHare called the “salient” poles; the polesMandPare called the “consequent” poles. The magnetic flow or field is shown by the dotted lines. On the periphery of the armature are wires in the slots shown. As this armature revolves, there will be a tendency for electricity to flow through the wires.

Fig. 236.

In order to distribute a current of electricity through these wires it is necessary to make a complete circuit. As each of the wires in the slots passes in front of a pole, a pressure or electro-motive force will be generated, and its direction will depend upon whether the pole is a North or a South pole,i.e., + or -.

Note.—In the above illustrations I and J represent the ordinary electric battery; in electrical literature such marks always indicate a battery.

The pressure or electro-motive force generated in the wires moving in front of the North, or positive field poles, will be in one direction, while that of those in front of the South, or negative field poles, will be in the opposite direction. Therefore, if two such wires be connected together at one end of the armature, the free terminals of the wires at the other end of the armature will have the sum of the electro-motive forces generated in the two wires. The wires so connected can be considered as a turn of a single wire instead of two separate wires, and this turn may be connected in series with other turns, so that the resulting electro-motive force is the sum of that in all the turns and all the wires so connected. It is customary to connect the coils of an armature so that the electro motive force given is that obtained from half the coils in series. The other half of the coils is connected in parallel with the first half, so that the currents flowing in the two halves will unite to give a current in the external circuit equal to twice the current in the two armature circuits or paths.

It is evident that, as the armature revolves, wires which were in front of the positive pole will pass in front of the negative, and that in order to maintain the electro-motive force it will be necessary to change the connections from the armature winding to the external circuit in such a way that all the wires between the two points of connection will have their electro-motive forces in the proper direction. The connection to the armature must therefore be made not at a definite point in the armature itself, but at a definite point with reference to the field magnets, so that all the wires between two points or contacts shall always sustain the same relation to the field magnets.

For this purpose a device known as a “commutator” is provided. The commutator is made up of a number of segments, as shown atA, inFig. 237, which are connected to the armature winding. On the commutator, rest sliding contacts, or brushes, which bear on the segments and are joined to an external circuit, making a continuous path through which current may flow. As the commutator revolves, the different segmentscome under the brushes, so that the relative position of the armature wires between the brushes is dependent on the position of the brushes. The armature wires which connect the brushes are those sustaining the desired definite position to the field magnets, so that the currents from the armature at all times flow properly into the external circuit, although individual armature wires carry currents first in one direction and then in the other direction, depending on the character of the pole in front of which they may be moving.

Fig. 237.

On two-pole machines there are two brush-holders, each containing one or more brushes. On the four-pole machine there may be either two or four brush-holders, and on a six-pole machine, either two, four, or six brush-holders.

A single path of the current through the commutator and armature winding is shown by the arrows onFig. 237. ThebrushesBandCare placed on the top side of the commutator to make them more accessible, and this shows a peculiar but simple armature winding.

For the sake of simplicity, the batteriesIandJ, ofFig. 236, are not used on common forms of generators or motors, but the current that flows from the armature through the commutator is made to flow through the electro-magnets either in whole or in part. If all of the armature current flows around the electro-magnets or fields of the machine, it is a “series” machine; if only a part of the current is used in this way, it is a “shunt” machine; that is, some of the current is “shunted” through the fields. Sometimes both the shunt and series windings are used, and in that case the machine is called a “compound wound” machine. Such a machine has a large wire through which the main current passes, and a fine wire through which the shunted current flows. Fig. 237 shows how the commutator and the fields are connected, and how the current flows from the wires in the armature through the commutator in a series machine.

If the current delivered by a dynamo does not flow in the desired direction, it can be reversed by shifting the wires in the binding posts or by throwing a switch. If the motor does not revolve in the desired direction, it can be made to do so by reversing the connections to the armature or field-coils; so that, without knowing which way a current of electricity is to be generated, any practical man can make a motor revolve in a proper direction by simply changing its connections.

It is natural that a machine which gives out electric energy when driven by an external power, should, when electric energy is delivered to it, reverse its action and give out mechanical power and do work.

Perhaps the simplest way to explain the cause of the movement of an electric motor, when supplied with a current, is to compare its action to the well-known attraction of unlike poles or magnets and the repulsion of like poles. Unlike poles are North and South; like poles are two North or two South. Inall motors a current through the field causes a North or South pole to be maintained, and a current through the armature and brushes causes an opposite polarity. These constantly-maintained unlike poles attract each other and pull the armature around on its axis.

It has been explained that if a motor be driven by a belt an electro-motive force is produced and the machine acts as a dynamo. It is also a fact that an electro-motive force is produced whether the power for driving the machine is received from a belt or from the electric current,—that is, whether the machine be driven as a dynamo or as a motor. In a dynamo, however, the current follows the direction in which the electro-motive force is acting. In a motor, the electro-motive force produced has a direction opposed to that of the flow of current. This may be illustrated by the following experiment.

Two similar machines are driven independently at 600 revolutions and give an electro-motive force of 100 volts. Similar terminals of the two machines are connected together; no current flows between the machines, because the two pressures are the same and are in opposite directions. If now the belt be thrown off from one machine, its speed will begin to fall; this will lower its electro-motive force below that of the other machine or dynamo, but will not change the direction of the force. There will now be a difference of pressure in favor of the machine which is driven, and it will deliver a current through the other machine and run it as a motor. The speed of the motor will continue to fall until the difference in pressure or electro-motive force between the two machines is only sufficient to cause the flow of enough current to keep the motor running against whatever frictional resistance, and other resistance there may be. The electro-motive force generated in the motor, which is against, or counter to that of the current in the circuit, is called the “counter electro-motive force.”

In order to determine how fast a motor will run without doing work under any given pressure, it is not necessary to know anything about the dynamo that furnishes the pressure.The pressure alone is sufficient to determine the speed of the motor. For instance, if a motor will give a pressure of 500 volts when running free at 100 revolutions, it will always run at about 100 revolutions when not doing work on an electric circuit where the pressure is 500 volts.

Thefigure on page 242shows a magnetic compass needle. This is used to test the direction of an electric current flowing through a wire or cable conductor. The plus sign, +, is the positive and the minus, -, sign is the negative end or pole.A continuous current always flows from the positive to the negative end or pole, hence the north end or pole, N, is the positive end of the needle and the south pole, S, is the south pole of the needle.

When one of these devices is held in close proximity to a conductor of electricityit immediately assumes a parallel position to the conductorand indicates the direction in which the current is flowing. The long, upper arrow, as shown in the figure, tells the direction of the flow. A small pocket compass may be used in place of this device and is often carried in the pocket of electricians for the purpose of indicating the direction of the current.

It should be understood that an electric dynamo or battery does not generate electricity, for if it were only the quantity of electricity that is desired, there would be no use for machines, as the earth may be regarded as a vast reservoir of electricity, of infinite quantity. But electricity in quantity without pressure is useless, as in the case of air or water, we can get no power without pressure, a flow of current.

As much air or water must flow into the pump or blower at one end, as flows out at the other. So it is with the dynamo; for proof that the current is not generated in the machine, we can measure the current flowing out through one wire, and in through the other—it will be found to be precisely the same. As in mechanics a pressure is necessary to produce a current of air, so in electrical phenomena an electro-motive force is necessary to produce a current of electricity. A current in either case can not exist without a pressure to produce it.

Since the conditions surrounding pumping plants are so widely different, it is impossible to treat every practical application in detail, hence, the space allotted to this subject has been used in the preceding succinct and plain discussion of the principles upon which electric power is applied to the operation of pumps.

The following are some of the advantages claimed for electric pumping machinery:

“Economy in operation and maintenance is the first and most vital consideration that demands the attention in the installation of pumping machinery. In respect to economy, the electric system has many important advantages. It is saving in the transmission of power, and thus enables a pumping installation to be situated at a considerable distance from the source of power where the first cost and maintenance expense of other systems would be almost prohibitive.

“The economy in space required is also worthy of consideration. The driving mechanism of a modern electric pumping outfit occupies a small amount of room and the space required for wiring is negligible. In case of accident, any mechanical injury to wires can be quickly and easily repaired—thus the economy in time and expenditure for repairs. There is no large loss by condensation. The only loss sustained with the electric system in the transmission of power is a small loss dueto line resistance, increasing directly with the amount of water being pumped and ceasing entirely when the pump is not in operation.”

A well designed electric pump will give an efficiency of from 75 to 80 per cent.; and, as the transmission loss depends upon the weight of copper in the transmission line it can be made as low as the cost of power, and, 2, the investment in copper will warrant.

1. It is important to locate the electric pump where it will be dry and clean and where it will be thoroughly accessible for proper care.

2. No pipes should be allowed to pass above the electric motor where liquids are likely to drip upon it.

3. The suction or supply pipe must be as short and straight as possible and must be air tight, as air entering the pump through the suction reduces its capacity or prevents it from working altogether.

4. A tight foot valve and a strainer should invariably be used on the bottom end of the suction pipe when the water is to be lifted from 8 ft. to 10 ft. below the pump. Where the lift is excessive or for any reason the supply be limited, an air chamber placed on the suction pipe near the pump will prove beneficial in preventing slamming of the valves.

5. Provision should be made for draining both pumps and pipes in cold weather by a proper application of frost cocks.

6. If the electric pump is keptdry, clean and well oiled, it will prove the most desirable and least expensive apparatus to be had for the service.

7. Ascertain the nature of electric current to be used. Direct or alternating? Voltage? (If alternating, note phase and number of alternations.)

8. Also record any unusual or peculiar circumstances connected with the installation or operation of the apparatus; and if so, what?

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