Inductor

“ Now let move on, still in contact with the earth-spring , till it comes into the middle of the inductor , the potential of which is . If is the coefficient of induction between and at this point, then, since the charge on will be .
When moves away from the earth-spring it carries this charge with it. As it moves out of the positive inductor towards the negative receiver its potential will be increasingly negative. At the middle of , if it retained its charge, its potential would be
and if is greater than its numerical value will be greater than that of . ”

“ Starting with a simple inductor cutting the lines of a magnetic field, such an analysis would gradually evolve in natural sequence the various combinations of inductors which constitute the windings of armatures and the typical forms which the complete machine is thence compelled to take, until, finally, the whole should culminate in the description of actual machines as manufactured, and the practical design of one or more dynamos for given outputs. ”

“ The current that arrives through L passes through the lightning protector, the body of the commutator, U, the terminal, v, and the call, W, bifurcates at P, and is closed by the earth. The inductor is in circuit, but, as it is in derivation, upon a very feeble resistance, v, nearly the whole of the current passes through the latter. When it is the station that is calling, the call, W, is put in derivation upon the circuit, f2 p, h, so that the portion of the circuit that passes through q W v is exceedingly feeble, and incapable of operating the bell of the post that is calling. ”

“ In a current generator a mass of iron, generally laminated, which is
moved past a magnet pole to increase the number of lines of force
issuing therefrom. It is used in inductor dynamos. (See Dynamo
Inductor.) In the cut Fig. 202, of an inductor dynamo i, i, are the
laminated inductors.
(b) In influence machines the paper or tinfoil armatures on which the
electrification is induced.
Inertia.
A force in virtue of which every body persists in its state of motion or
rest except so far as it is acted on by some force.
Inertia, Electro-magnetic. ”

“ When the inductor turns to the second position magnetism can get across without flowing through the core, for the blocks now give it a path. As the flow through the core ceases, the core’s magnetism dies away, which gives the change in strength that is needed to produce a sparking current. ”

“ The inductors and receivers are so formed that when the carriers arrive at certain points in their revolution they are almost completely surrounded by a con ducting body. As the inductors and receivers cannot completely surround the carrier and at the same time allow it to move freely in and out without a complicated arrangement of moveable pieces, the instrument is not theoretically perfect without a pair of re generators, which store up the small amount of electricity which the carriers retain when they emerge from the receivers. ”

“ The tendency at the present time whatever the voltage, is towards the use of machines with stationary armatures and revolving field magnets, or towards a pure inductor type having all its windings stationary. At moderate voltages such an arrangement is merely a matter of convenience, but' in high-voltage generators it is practically a necessity. Low-voltage machines are usually provided with polyodontal windings, these windings having several separate armature teeth per pole per phase, while the high-voltage machines are generally monodontal ”

“ The effect of embedding the armature inductors in slots is to distort the magnetic field as shown in fig. 296. Most of the lines of force pass through the teeth, thus, not only are the inductors better placed for driving purposes, but, being screened magnetically by the teeth, the forces acting on them are reduced, the greater part of the magnetic drag being taken up by the core. ”

“ Cheap construction, maximum voltage for a given number of inductors. Concentrated windings have greater armature reaction and inductance than other types hence the terminal voltage of an alternator with concentrated winding falls off more than with distributed winding when the current output is increased. An alternator, therefore, does not have as good regulation with concentrated winding as with distributed winding. ”

“ This armature is an example of heavy duty construction. The inductors are welded to the short circuiting end rings, the latter being located beneath the inductors, as shown. Fan vanes are provided at one end for ventilation. In the field construction, the core laminations are assembled in a closed box frame, and clamped by heavy rings while under hydraulic pressure. The stator coils are form wound and subjected to a special insulating process, which renders them especially impervious to moisture, and capable of operating without breakdown in locations which are too damp for ordinary motors. ”

“ To connect up rightly the inductors on an armature so as to produce a desired result is a simple matter in the case of ring winding, for bipolar or multipolar machines. It is a less easy matter in the case of drum winding, especially for multipolar machines. ”

“ There is usually sufficient charge on one of the inductors to start the machine, but in damp weather it will often be found necessary to apply a charge to one of the inductors by means of the ebonite or glass rod before the machine will work. ”

“ For multiplying small differences of potential. The inductors may be charged at first to an exceedingly small potential, as, for instance, that due to a thermo-electric pair, then, by turning the machine, the difference of potentials may be continually multiplied till it becomes capable of measurement by an ordinary electrometer. By determining by experiment the ratio of increase of this difference due to each turn of the machine, the original electromotive force with which the inductors were charged may be deduced from the number of turns and the final electrification. ”

“ Fig. 1,373.—Developed view of elementary two phase four pole alternator and sine curves, showing the alternating current or pressure generated during one revolution of the armature. The complete winding for the three phases are here visible, the field magnets being represented as transparent so that all of the inductors may be seen. By applying Fleming's rule, as the inductors progress under the poles, the directions and reversals of current are easily determined, as indicated by the sine curves. It will be seen from the curves that four poles give two cycles per revolution. ”

“ Several other electrical machines have been constructed in which the principle of electric induction is employed. Of these the most remarkable is that of Holtz, in which the carrier is a glass plate varnished with gum-lac and the inductors are pieces of pasteboard. Sparks are prevented from passing between the parts of the apparatus by means of two glass plates, one on each side of the revolving carrier plate. This machine is found to be very effective, and not to be much affected by the state of the atmosphere. ”

“ Evolute or Butterfly Winding.—This mode of winding, was introduced by Siemens for electroplating dynamos to overcome the objections to hand winding. It takes its name from the method of uniting the inductors by means of spiral end connectors as shown in fig. ”

“ But when the positive half of an alternating current is made to flow through a large inductance it acts like a large resistance as before and likewise smooths out the current, but none of its energy is wasted in heat and so a coil having a large inductance, which is called an inductive reactance, or just reactor for short, is used to smooth out, or filter, the alternating current after it has been changed into a pulsating direct current by the rectifier tubes. ”

“ If now an iron core be gradually pushed into the coil, the self-induction will be greatly increased and the lamp will go out, thus showing the great importance which self-induction plays in alternating current work.
Inductance.—Each time a direct current is started, stopped or varied in strength, the magnetism changes, and induces or tends to induce a pressure in the wire which always has a direction opposing the pressure which originally produced the current. This self-induced pressure tends to weaken the main current at the start and prolong it when the circuit is opened. ”

“ Evidently therefore the characteristic curve connecting armature current and terminal volts will with a constant exciting current depend on the nature of the load, whether inductive or non-inductive, and upon the amount of inductance already possessed by the armature itself. With an inductive load it will fall more rapidly from its initial maximum value, or, conversely, if the initial voltage is to be maintained under an increasing load, the exciting current will have to be increased more than if the load were non-inductive. ”

“ Thus the Leyden jar L and associated coil P shown in Fig. 82, p. 271, constitutes an electric circuit, having a certain capacity measured in units, called a microfarad, and a certain inductance, or electric inertia measured in centimetres. The capacity of the circuit is the quality of it in virtue of which an [291] electric strain or displacement can be made by an electromotive force acting on it. The inductance is the inertia quality of the circuit, in virtue of which an electric current created in it tends to persist. ”

“ In all these investigations, in all these experiments, which are so very, very interesting, for many years past--ever since the greatest experimenter who lectured in this hall discovered its principle--we have had a steady companion, an appliance familiar to every one, a plaything once, a thing of momentous importance now--the induction coil. There is no dearer appliance to the electrician. From the ablest among you, I dare say, down to the inexperienced student, to your lecturer, we all have passed many delightful hours in experimenting with the induction coil. ”

“ Inertia is that property of a material body that requires time and energy to set in motion, or stop. Inductance is that property of an oscillation circuit that makes an electric current take time to start and time to stop. Because of the inductance, when a current flows through a circuit it causes the electric energy to be absorbed and changes a large part of it into magnetic lines of force. Where high frequency currents surge in a circuit the inductance of it becomes a powerful factor. ”

“ Modern machines depend upon the principle of induction. The electrophorus (Exp. 68) is really a very simple form of induction machine. The potential of these machines is very great, as the spark may jump many inches. Thousands of Galvanic cells would be needed to make a spark an inch long. When the spark passes through the air it meets with an extremely high resistance, as air practically insulates ordinary electricity. This high resistance in the circuit reduces the strength of the current. While the potential is very high, the strength of the current is very low. (See Ohm's Law.) ”

“ If an alternating or intermittent continuous current is passed through the primary circuit, it creates an alternating or intermittent magnetization in the iron core, and this in turn creates in the secondary circuit a secondary current which is called the induced current. For most purposes an induction coil is required which is capable of giving in the secondary circuit intermittent currents of very high electromotive force, and to attain this result the secondary circuit must as a rule consist of a very large number of turns of wire. ”

“ If the electromotive force is raised above twenty-five volts, then if there is no inductance in the circuit, the continuous flow of current proceeds, but if the circuit of the electrolyte possesses a certain minimum inductance, the character of the current flow changes, and it becomes intermittent, and the cell acts as an interrupter, the current being interrupted from 100 to 2,000 times per second, according to the electromotive force, and the inductance of the circuit. Under these conditions, the cell produces a rattling noise and a luminous glow appears round the tip of the platinum wire. ”

“ The lamp must always be adapted to the current or the current to the lamp, as you choose. The human body may be placed in a circuit where such low voltage is used without dan [Pg 202] ger, but it would be exceedingly dangerous to be put in contact with a pressure of 1000 or more volts, such as is used for lighting purposes.
In principle the transformer is nothing more or less than an induction-coil on a very large scale. The ordinary induction-coil, such as is used for medical purposes, is ordinarily constructed by winding a coarse wire around an iron core. ”

“ An induction motor will operate only on alternating current.
A small motor such as that shown in Figure 267, and having a three-pole armature, is the best type to use in making an experimental induction motor.
Remove the brushes from the motor and bind a piece of bare copper wire around the commutator so that it short-circuits the segments.
A source of alternating current should then be connected to the terminals of the field coil. If you have a step-down transformer, use it for this purpose, but otherwise connect it in series with a lamp bank such as that just described. ”

“ Induction appears to consist in a certain polarized state of the particles, into which they are thrown by the electrified body sustaining the action, the particles assuming positive and negative points or parts, which are symmetrically arranged with respect to each other and the inducting surfaces or particles. The state must be a forced one, for it is originated and sustained only by force, and sinks to the normal or quiescent state when that force is removed. It can be continued only in insulators by the same portion of electricity, because they only can retain this state of the particles. ”