Electric motor

“ Motors are rated by horsepower, and generators are rated by kilowatts. Thus a one kilowatt generator has a capacity of 1,000 watts; as a motor, it would be rated as 1000/746 horsepower, or 1.34 horsepower. Their efficiency varies with their size, ranging from 40 to 60 per cent in very small motors, and up to 95 per cent in very large ones. The following table may be taken as a guide in calculating the power required by motors, on 110-volt circuits:
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An electric motor, in operation, actually generates electricity, which it pushes back into the line as a counter-electromotive-force. ”

“ In order to give different speeds and to enable the amount of current taken by the motors at starting to be reduced, arrangements must be made for connecting either the motors or the parts of the motors, or the two halves of the battery, or both in different groupings. It must be pointed out that more current can be put into an electric motor at starting than when running, owing to the fact that when running it produces a kind of back electric pressure. ”

“ The electric motor is also exceedingly compact. As regards the amount of space it occupies, it compares favourably with any other form giving the same amount of power. As regards weight it is slightly heavier than the petrol motor. ”

“ An Electric Motor is really a machine. If it be supplied with a proper current of electricity, its armature will revolve; and, if a pulley or wheel be fastened to the revolving shaft, a belt can be attached, and the motor made to do work. There are many kinds of motors, and many simple experiments which aid in understanding them. ”

“ The compound motor has the characteristics of the series and shunt motors, giving an increased starting torque, and a more nearly constant speed under varying loads than the shunt motor, since the latter drops off slightly in speed with increasing load.
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Flexible Power
An electric motor is an extremely satisfactory form of power because it is so flexible. Thus, one may use a five horsepower motor for a one horsepower task, and the motor will use only one electrical horsepower in current—just enough to overcome the task imposed on it. ”

“ The motors may therefore be reduced in size, saving money in first cost and in the current consumed.
The second valuable peculiarity of the electric motor is that it gives its 'maximum torque' at starting. That is to say, it exercises the highest propulsive effort at the precise moment when it is required. When horses are employed, they have to endure an abnormal strain in overcoming the inertia of a stationary vehicle; everyone must have noticed how horses have to struggle to start a car which they can keep going at an easy trot once it has got up speed. ”

“ In this system the power of the car engine is used to drive an electric dynamo. This dynamo generates current which is either supplied direct to electric motors or else stored in a battery of accumulators, the former method being the better and more likely to survive. Sometimes one electric motor is used, taking the place of an ordinary gear box, and driving the back wheels through a universally jointed shaft and a differential gear. ”

“ Having got your electric motor it would seem a comparatively easy job to mount it on a car, to fix up a moving connection with an electric wire, and to make the motor turn the car-wheels. It looks easy enough to-day in places where hundreds of horseless cars are running about in all directions as if by magic. ”

“ On the passage of an electric current through the wire, a continuous rotary motion was produced in it, the direction of which depends both on the direction of the current, and on the polarity of the end of the magnet around which the rotation occurs.
The great value of the electric motor to the world is too evident to need any proof. The number of purposes for which electric motors are now employed is so great that the actual number of motors in daily use is almost incredible, and every year sees this number rapidly increasing. ”

“ In the illustration, Fig. 32, [56] is shown a modern electric motor. It is a Westinghouse two-phase machine, of 300 horse power, of the self starting induction type, designed to operate at a speed of 500 revolutions per minute when supplied with two-phase currents of 3,000 alternations per minute and 2,000 volts pressure.
FIG. 33.—SIEMENS’ FIRST ELECTRIC RAILWAY.
The most important application of the electric motor is for street car operation. ”

“ Motors operated by electricity have been devised to propel everything from a bicycle to a locomotive. Electric power is sometimes conveyed to the motor from a waterfall and sometimes from a storage battery. In any simple electric motor one finds a field-magnet, consisting of various coils of insulated wire on soft iron cores. ”

“ On level, easy roads, where the power required falls below the maximum power exerted by the benzine motor, the electric motor changes automatically to a dynamo and the surplus force of the benzine motor is converted into current and stored. In running down hill or stopping the carriage, the momentum of the vehicle is also received by the electric motor acting as a dynamo and brake, and is stored as electricity in the battery, which is thus in an ordinary journey kept constantly charged. ”

“ The solution was found by making the two wheels move by means of a timing fork, which vibrates with the same speed everywhere, and under all conditions.
Electric Motor.—The direct current electric motor depends for its action on the principle that likes repel, and unlikes attract. The commutator so arranges the poles that at the proper points, in the revolution of the armature, the poles are always presented to each other in such a way that as they approach each other, they are opposites, and thus attract, and as they recede from each other they repel. ”

“ To milk cows by electricity is simply to apply the vacuum-cleaner idea to the process, and, in general, doing things by electricity usually means doing them by some machine that is made to go by an electric motor. This then is the first key to the Electrical Show, and if you will remember to look first for the motor it may remove much of the mystery from some of the exhibits. In many cases it is not necessary to have a complete electric motor, but simply an electro-magnet to do the work. ”

“ An electric motor of small power—about eighteen kilogrammetres per second—controls the shaft on which the three rotary brushes are fixed, and the customer has only to unlock the machine, the same as all others of its kind, with his coin, and move the handle which opens the circuit and starts the motion. ”

“ An electric motor is a machine which produces rotary movement owing to the magnetic action caused by an electric current.
Everyone is doubtless familiar with the ordinary magnet, a piece of steel either straight or, more often, shaped like a horseshoe, possessing the property of attracting certain metals which are termed magnetic, or more accurately para-magnetic. Nickel and iron are amongst those which are attracted, but iron is much more powerfully attracted than nickel. ”

“ An electric motor is small and compact, gives off no fumes and practically no heat, makes very little noise, is capable of running for very long periods at high speed and with the utmost steadiness, and requires extremely little attention. ”

“ The machine gets charged after a few turns of the handle, and the operator feels that, as the charging progresses, it gets harder to turn the handle. In large machines the manual work becomes so heavy that it is convenient to use an electric motor for working the machine. ”

“ And when, starting from the researches of Siemens, Wilde, Nollet, Holmes and Gramme, the modern forms of magneto-electric and dynamo-electric machines began to come into commercial use, it was discovered that any one of the modern machines designed as a generator of currents constituted a far more efficient electric motor than any of the previous forms which had been designed specially as motors. ”

“ The little electric motor may be designed, on the other hand, to have almost as high an efficiency as the large motor. And while the loss of energy due to condensation in long steam-pipes is most serious, the loss of energy due to transmission of electric current in mains of equal length is practically negligible. ”

“ Thus, a one kilowatt plant permits the use of any one of these lamp circuit devices at a time, with a few lights in addition.
Power
Electric power is to be had through motors. A direct current dynamo and a direct current motor are identical in construction. That is, a motor becomes a generator if belted to power; and a generator becomes a motor, if connected to electric mains. ”

“ Then his fingers waited on the switches.
"But Doug, the fan motors will only work on house current—"
"Yes, that's right, but I've geared—pulleyed, I mean—two of them up, so that they'll turn the other two at least twice their normal armature speed. And the simple electric motor works—"
"—in reverse, too, doesn't it! If you turn it by mechanical means, it generates electric current!"
"That's about it. I ought to get about five hundred volts from each, with the pulley ratio I'm using. And they're both connected in series, so—a thousand volts, I hope. ”

“ Electric motor service is much less exacting as to constancy of voltage, and the pressure at motor terminals may sometimes be varied as much as ten per cent without material objection on the part of users. A mixed service to these three classes of apparatus must often be provided where transmitted energy is used, and the limitations as to variations at incandescent lamps are thus the ones that must control the regulation of pressure. ”

“ Assuming a vehicle with running gear complete and motors mounted and geared to the driving-wheels, the motors have to be fed with energy in order that the car may be propelled— that is to say, we must in addition to the motors have a source of electric current present. A car with body, running gear, and motors geared in position, is a potentiality only. ”

“ The motors supplied are an advantageous adjunct, inasmuch as they provide a day load, increasing the output of the station at a time when the lighting load is small and when the machinery in consequence would, without them, have remained idle. The growth of the application of electric motors in the closing years of the century has been phenomenal, even leaving out of consideration their use in electric railways.
Twenty years ago an electric motor was a curiosity; fifty years ago crude examples run by batteries were only to be occasionally found in cabinets of scientific apparatus. ”

“ As it does this the brushes connect with other commutator
sections, and the poles of the armature are shifted back. This action
continues indefinitely.
Another class of motors is of the reciprocating type. These are now very
little used. (See Motor, Reciprocating.)
One valuable feature of continuous rotation electric motors is the fact
that they absorb energy, to a great extent proportional in amount to the
work they have to do. The rotation of the armature in the field of the
motor involves the cutting of lines of force by its coils. ”

“ Notice that when the compartment j is full of air and the side d e, is lifted to its greatest height the strip n is moved to the lowest point p, and the electric current must pass from u through all the resistance of the rheostat in order to get back to the armature by the wire t. This makes the motor go very slowly. When d e sinks down, the strip n moves to the upper points p, and the resistance is reduced step by step, enabling the motor to quicken its speed and pump faster as more air is required.
Small motors in order to be effective must travel at high speed. ”

“ It's guaranteed to run the car under electric power for nearly a mile, without the motor being operated. All we'll have to do will be to set the starter going—that turns the fly wheel, you know. Then we can put in low gear, slip in the clutch, just as if the motor was in operation, and get the car to the top of the hill. ”

“ As the batteries also, when arranged in parallel groups, are able to yield a heavier current, the arrangement is mutually satisfactory to both batteries and motors. For reversing, the controller is brought into such a position as to send the current the reverse way through the motor.
An electric car does not require change-speed gear because it contains practically a gear in itself. It accommodates itself to the load and does its best at any given load, or by varying the electric pressure it may be caused to increase or diminish its power within limits. ”

“ In the telephone for nearly two thousand miles the pulsations of the speaker's voice are not only audible, but retain their characteristic tones.
In the field of mechanics electricity is decidedly preferable to any other agent. Heat may be transformed into motive power by a suitable engine, but there its adaptability is at an end. An electric current drives not only a motor, but every machine and tool attached to the motor, [Pg 136] the whole executing tasks of a delicacy and complication new to industrial art. ”

“ The point motors are connected direct to the points; but between a signal motor and its arm there is an "electric slot," consisting of a powerful electro-magnet which forms a link in the rod work. To lower a signal it is necessary that the motor shall revolve and a control current pass round the magnet to give it the requisite attractive force. If no control current flows, as would happen were any pair of points not in their proper position, the motor can have no effect on the signal arm to lower it, owing to the magnet letting go its grip. ”