Electrical coil

“ The induction coil has always been a popular piece of apparatus with those interested in electrical science; the experiments which can be performed with its aid are very numerous. It is of considerable importance, especially in its application to such useful purposes as X ray work, wireless telegraphy and ignition for gas engines. The latter has caused manufacturers to give much attention to the development of the induction coil, resulting in many refinements of design and construction. ”

“ Terminals, each having a 1⁄2 inch round hole, to accommodate the conductors are provided at each end of the coil. Three square headed binding screws are supplied which clamp the conductors in position. The coil is provided with a strain insulator, so arranged within the coil at its axis, that it assumes any mechanical tension transmitted from the conductors. No mechanical tension reaches the turns of the choke coil proper. In construction, the choke coil is made in but one size having a current carrying capacity of 200 amperes and is suitable for a voltage of 2,000 to 22,000. ”

“ Large cars are often fitted with both systems, so as to have one in reserve should the other break down.
Electrical ignition is most commonly produced by the aid of an intensity coil, which consists of an inner core of coarse insulated wire, called the primary coil; and an outer, or secondary coil, of very fine wire. A current passes at intervals, timed by a cam on the exhaust-valve gear working a make-and-break contact blade, from an accumulator through the primary coil, exciting by induction a current of much greater intensity in the secondary. ”

“ Thus one coil may be in
parallel with the other, and the action on the plunger will then depend
on the relative currents passing through the coils.
Coil, Choking.
A coil of high self-induction, used to resist the intensity of or
"choke" alternating currents. Any coil of insulated wire wound around
upon a laminated or divided iron core forms a choking coil. The iron
coil is usually so shaped as to afford a closed magnetic circuit.
A converter or transformer acts as a choking coil as long as its
secondary is left open. ”

“ Current is flowing through the shunt coil continuously, even when no energy is being taken, and the higher the inductance of this coil, the smaller will be the energy component of the constant flow. The series coil causes a loss of energy proportional to the square of the current flowing. It also causes a drop in voltage, both inductive and resistive, hence, the resistance and inductance of the series coil of the meter should be as low as possible. ”

“ The end of one coil must be joined to the beginning of the other properly, or the action of one will destroy that of the other. Fig. 89 shows the two coils, A and B. If the current enters at the binding-post, X, it will pass through the turns of coil A, in the direction of clock-hands, then out to Y, where B begins, around B in the same way, and then to Z. Y may be [Pg 86] simply a screw-eye binding-post (App. 41) . By this arrangement one or both coils can be used at a time. If the current is very weak, use both coils ”

“ The lighting load is entirely connected to one single phase circuit, and the motors are started and operated from this circuit with the assistance of the teazer wire. The long coil indicates the main winding of the armature, which is similar in its arrangement and size to the ordinary armature winding of a single phase alternator. The short coil which connects at one end to the middle point of the coil above mentioned, and at the other to a third collector ring is called the "teazer" coil. Its use is to generate a pressure in quadrature with that of the main coil. ”

“ Primary Induction Coils.—These represent the simplest form of coil, and are used chiefly in low tension ignition to intensify the spark when a battery forms the current source.
A primary coil consists of a long iron core wound with a considerable length of low resistance insulated copper wire, the length of the core and the number of turns of the insulated wire winding determining the efficiency. The effect of the iron core is to increase the self-induction. ”

“ Binding-Post. Fig. 27. A coiled spring serves very well as a connector. One end should be fastened to the apparatus, as shown, by clamping it under a screw-head. The other end of the coil should be pulled out a little, away from the other turns, so that you can stretch the spring in order to put the bare ends of wires between the turns. Any number of wires placed between these turns will be pinched and electrically connected. The coil should be about 1⁄2 in. long and less than 1⁄2 in. in diameter. You can make a coil by tightly wrapping stiff iron wire around a pencil. ”

“ The number of insulators used in the columns depends on the voltage of the circuit in which the coil is to be used. The apparatus can be mounted in any position convenient for the wiring, on floor, wall, or ceiling. It is intended principally for the protection of transformers. Where greater reactance than is afforded by a single coil is desired on the higher voltage circuits, it is recommended that two or more coils be connected in series, one coil being used for each 22,000 line voltage. ”

“ It should be noted that the coil is always in circuit, as is the case with the overload and underload coils, and that it operates with the releasing of its armature. It is always necessary to use a fixed amount of resistance (depending upon the voltage of the system) in series with the low voltage release. The low voltage release performs the functions of a shunt trip coil when used in conjunction with a push button, auxiliary switch or speed limiting device, and is generally preferred to the shunt trip attachment.
[Pg 1635]
Fig. ”

“ It is necessary, in order that shocks should be obtained from the coil, that the current in the primary wire should be stopped and started again at the rate of several hundred times per minute, and the more quickly the contact between the battery wire and the primary coil is made and unmade the more powerful the shock. ”

“ A coil has an inductance of one henry when the product of the number of lines enclosed by the coil multiplied by the number of turns in the coil, when a current of one ampere is flowing in the coil, is equal to 100,000,000 or 108.
An inductance of one henry exists in a circuit when a current changing at the rate of one ampere per second induces a pressure of one volt in the circuit. ”

“ What is the effect of a short circuit in the field coils or field circuit?
Ans. The machine generally refuses to excite.
Ques. How are the field coils tested for short circuit?
Ans. By measuring the resistance of each coil with an ohmmeter or Wheatstone bridge. The faulty coils will show a much less [621] resistance than the perfect coils. The fault may also be discovered and located by passing a strong current from a battery or another dynamo through each of the coils in turn, and observing the relative magnetic effects produced by each upon a bar of iron held in their vicinity. ”

“ An induction coil arranged to have a lower electro-motive force in the
secondary than in the primary. This is effected by having more
convolutions in the primary wire than in the secondary. Such coils in
practice are used with the alternating current and then do not include a
circuit breaker or condenser. They are employed in alternating current
system and in electric welding. (See Welding, Electric--Converter.) ”

“ At sea the wire would run to one or more metal plates on the bottom of the vessel, where the earth connection would be made with the water. The high-resistance secondary circuit of an induction coil is located in circuit between the condensing surface and the ground. The primary circuit of the induction coil includes a battery and a device for transmitting signals, which may be a revolving circuit-breaker operated continually by a motor of any suitable kind, either electrical or mechanical, and a key normally short-circuiting the circuit-breaker or secondary coil. ”

“ On balanced load, the coils take a small alternating exciting current from the collector rings as any transformer does when connected to an alternating current line with its secondary open. When an unbalanced load comes on, the current in the neutral divides, half going to each coil. This enters the coil at the middle point and half flows each way through the coil and 717 the slip rings into the armature winding. The unbalanced current is thus fed back directly into the dynamo armature continuously. ”

“ Steel tapered keys are driven in alongside the dovetails, and the pole pieces cannot become loose. All field coils, except on a few of the smallest machines, are of edgewise wound copper strip. This style of coil is essential for revolving field alternators where the pressure on the insulation, due to centrifugal force, is so great that cotton insulation on round wire will not stand. Current is led into the rings by means of carbon brushes, the number of brushes being such that the current density at the rubbing contact is kept within conservative limits. ”

“ In actual practice, when the wire is run through the paraffin bath not more than 50 per cent of the calculated wire will occupy the space. And the thickness of the paper rings must also be added when figuring the total length of the coil. In the iron-clad transformers or induction coils of highest efficiency used in the alternating current electric light system, the rule for determining the windings of the coils is based on the ratio of the turns of wire in the primary to the turns in the secondary, the electromotive force in the primary, and the lines of force cut by the windings. ”

“ The current supply available will determine the type of the instruments, and whether an induction coil or a transformer is used. Unless current mains for light and power are already installed, it must be generated by an engine and dynamo, or recourse had to batteries. Induction coils may be operated on either direct or alternating current. Dry cells are most commonly employed to furnish the current for small induction coils, but a storage or some form of renewable primary cell, such as the Fuller and Edison, is necessary if the coil is a large one. ”

“ By means of a large induction coil we can obtain a voltage hundreds or even thousands of times greater than that of the original battery current, but on account of the great resistance of a very long, thin wire, the amperage is much smaller. The induction coil produces a rapid succession of sparks, similar to those obtained from a Wimshurst machine. A coil has been constructed capable of giving sparks 421⁄2 inches in length, and having a secondary coil with 340,000 turns of wire, the total length of the wire being 280 miles. ”

“ Connecting wires, properly protected, lend from the coil to a differential voltameter, so that, by means of the current from a battery circulating in the system, the electric resistance of the coil in the furnace can be determined at any moment. ”

“ A coil much used for electric baths has a primary winding only, regulated by the sliding in and out of the iron core, which necessitates the use of an independent vibrator, or else by varying the current strength with a rheostat. The general directions given before will answer in the present case, the only data necessary being the size of wire, which should be about six to ten layers of No. 20 B & S. The coil with movable secondaries here comes into service. Strong currents are needed for bath work, and any variety of winding can be used with this make of coil. ”

“ The intensely disruptive power of the long spark is readily shown by its power to perforate substances, but great care must be taken that the secondary wires of a coil are led away from the body of the coil. A good plan is to hang two silk cords or stout threads from the ceiling, to which the secondary wires may be attached and kept in sight when experimenting at any distance from the coil. ”

“ These are the cylinders shown in Fig. 130. They simply contain a great many coils of copper wire with a vast amount of iron at the centre. They accomplish in a large way what our spark coil does in a lesser degree. But why go to all this expense to produce such a dangerous and troublesome voltage? The answer briefly is, that while it is dangerous and troublesome the expense is not so great as it would be to supply by any other method the electric current required. Denver and numerous other places, large and small, require electric current. ”

“ In coils with independent circuit breakers, sliding both core and primary coil out of the secondary together or independently. (b) Moving a metal tube over or off the primary coil or core or both. Many combinations of these methods are practised. Attempts have been made to regulate battery current by rheostat,52 but it is not feasible, except in large stationary outfits. Cheap medical coils are wound with bare wire, with layers of thread between adjacent turns, or even only bedding the wire turns in paraffined paper. ”

“ It is, of course, absolutely necessary to employ in such a coil wires provided with the best insulation. Good coils may be produced by employing wires covered with several layers of cotton, boiling the coil a long time in pure wax, and cooling under moderate pressure. The advantage of such a coil is that it can be easily handled, but it cannot probably give as satisfactory results as a coil immersed in pure oil. ”