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ELECTRICAL TRANSMISSION OF POWER
FOR COTTON MILLS.
By Mr. C. J. H. WOODBURY, Lynn, Mass.
Every one of the numerous applications of electricity, excepting incandescent lighting and chemical processes, as electroplating, requires the use of electric motors; and some types of dynamos used for incandescent electric lighting contain a regulator which is operated by a motor.
The telegraph receiver is a motor in which the electric impulses produced by the work at the operator's hands at the sending key converts the electricity from the batteries into work. In like manner, electric bells, watchmen's record clocks, railway signals, fire alarms, and even telephones, all are examples of motors. Mr. Edison once exhibited to me a telephone in which a small rod attached to the diaphragm of the receiving telephone was fitted with mechanism by which its rapid longitudinal vibration was converted into circular motion, causing a tiny wheel to revolve very rapidly.
The experiments of Barlow in 1826, by which an electromagnet was used to cause a continuous revolution, gave rise to many ingenious inventions of devices for producing rotary motions by electricity; some of the experiments being on a large scale, so extensive, indeed, that a yacht was propelled by one fifty-four years ago, and a railway car forty-one years ago. All of these used the alternate attraction and release of an electro-magnet, giving a reciprocating motion to an armature, and this was easily converted into rotary motion. These devices obtained their electricity from batteries, and were comparable as a matter of principle to a device which might be made by attaching a tiny connecting rod and crank to a telegraph receiver. None of these early electric motors were of any practical value whatsoever in serving for motive power.
The electric motor which is the live issue of to-day is based on the principle that, while a dynamo will generate electricity if power is applied to revolve the armature, yet, on the other hand, if electricity is applied to the dynamo, the armature will revolve. The machine is reversible ; and this reversibility has been wisely called by that eminent mechanician, the late Clerk Maxwell, the greatest invention of the century.
It undoubtedly resulted, as far as public attention was ever called to the matter, from a blunder of a workman engaged in putting up some electric lighting apparatus at the Vienna Exhibition in 1873, by which the wires were connected to one dynamo at one end and to another dynamo at the other end, and when one dynamo started, to the surprise of all, the other was set into rapid motion. As is usually the case with such inventions, there are others who allege that this well-attested incident was the result of design, to illustrate the discovery which they claim to have made previously.
It has been recently found that Dr. Antonio Pacinotti, the inventor of a magneto-electric machine, wrote a description of his machine in an Italian periodical in June, 1864, in which he says that it can be used to generate electricity, or as a motor; and he therefore is entitled to the credit for the invention of the present electric motor.
The relation between magnetism and electricity, by which the magnet of an electric motor can set in revolution by its attraction the copper wires conducting electricity in the armature of an electric motor, is well illustrated by applying a magnet to an incandescent lamp. When the lamp is not illuminated the magnet will not produce any effect upon it, but if the lamp is in use the magnet will attract the filament.
The same machine can and has frequently been used at värious times as a dynamo for electric lights and at other times for a motor; but there are numerous mechanical and electrical modifications essential to obtain the best results in an electric motor. The first use of an electric motor in any of the cotton mills represented in this Association occurred in a thread mill in Newark, where a dynamo was used in 1882 as a motor to run a lot of thread-winding machines.
Electric motors are now used for hundreds of purposes, but this paper
will be confined to references to their uses in cotton mills.
Electric motors are frequently proportioned to use low-pressure currents of electricity, like those employed for direct incandescent lighting.
There are many places where motors can be operated by wires from any of the direct incandescent lighting dynamos ; but, if the power required for the motor is more than about one-fifth that required to keep the whole number of lamps lighted, the lights will rise and fall in brilliancy, like those in an electric car when the motor starts and stops, the lighting service is unsatisfactory and the life of the lamps diminished.
The problem is one which must be worked out in each case; sometimes, when a small motor is required for use at short intervals during the day, it might be the more economical to use conductors from a large dynamo which is already installed for lighting the mill at other times. If constant service is required from the motor, then a separate generating dynamo is advisable; and it may be said that in the generality of work it is preferable to put in a generator suitable for furnishing the current to the motors.
The principle holds as good in electric apparatus as in all other machinery, — that more satisfactory results are obtained
when there is no attempt made to require a more varied service from any machine than it is fully adequate to furnish.
It is generally advisable to use electricity for the transmission of power at a much higher pressure than that found best
suited to incandescent lamps, because there is a great saving in copper for conductors, and a lesser proportion of the electricity absorbed by the resistance of the wires.
The current of five hundred volts' pressure used for the trolley system of street-car propulsion is not capable of inflicting serious injury upon mankind, although frequently fatal to horses. There have been motors suited for use on arc-lighting circuits, but I believe that at the present time there are not any of them on the market.
Before deciding to install an electric power plant for a service outside of what is already fixed by precedent, expense, delays and disappointment may be avoided by deciding how much you are willing to experiment; and, secondly, how much the party doing the work must experiment before the whole installation is in a practical operating condition.
The fact should not be lost sight of that electricity is merely a substitute for other methods of transmission of power.
It has its losses at every step in the course, comparable with those of the wear and tear and friction of shafting and belting. Like them, it also costs money, requires attendance, and wears out. It does not in any detail give something for nothing, but the results in comparison with other mechanical means of the transmission of power are merely the addition of a lot of differences. Sometimes these differences are on one side of the account and sometimes on the other.
An installation of motors in one instance may be extremely economical and in another highly expensive, in comparison to ordinary methods of transmission of power.
Electric motors, like water wheels or steam engines, have their highest efficiency at a point near to their full proper load, and on either side their efficiency in the percentage of electricity converted into work is diminished. The practical operation of some motors has been improved by the use of fly-wheels.
In its application for mill service, the most simple uses are those requiring a variable speed and direction, largely on account of causes outside of the electrical conditions in the construction of such motors. It is especially advantageous for elevators in storehouses or other buildings not requiring power elsewhere. A motor can be attached to any elevator machinery operated by a belt, and the elevator can be managed in the same manner as before, so that the men have nothing either to learn or to forget. The first motor used for operating an elevator in a cotton-mill store-house was placed in that service in 1882, and is in as good working condition to-day. Another use having a larger field is in its application for railways in mill yards and buildings. The Salmon Falls Manufacturing Company has twenty-one hundred feet of track in the mill yard, and is operating a trolley system of cars to move all their cotton, supplies, cloth and coal, with two men, thereby dispensing with the services of a team and three men all of the time, and a fourth man a part of the time. The car makes an average speed of six hundred feet per minute, and is always ready for service whenever the water wheel is running. Other mills use electric railroads from the cloth room to the store-house with even greater reduction in cost of moving the load.
There are two systems of overhead trolley propulsion; the ordinary single overhead wire, with the current returning through the wheels to the rails and thence back through the earth to the dynamo, is the simplest and the only one that has a practical system of switches in the wires overhead. This system contains a serious objection, in the electric sparks constantly occurring in the contact of the wheels with the rails, and liable to ignite any combustible substance there, and therefore could not be safely used inside of mills. For inside use it is necessary to use the double overhead wire system by which the circuit is made between the two wires, without using the rails as conductors. In either case the overhead wires should be thoroughly protected by guard wires whenever there is a possibility of telephone or other wires falling upon them.
Electricity is filling a most useful purpose in operating travelling cranes, and the few store-houses in mills which are provided with travelling cranes use them at such infrequent