US1853548A - Coil - Google Patents

Description

April 12, 1932. w. L.-CASPER .COIL

Filed Npv. 10, 1928 wmwMMm864 INVENTOR W. L. CA SPER 5:;

A r Tom/B Patented Apr. 12, 1932 UNlrEnj-sTATEs PATENT OFFICE WILLIAM L. CASPER, OF SUMMIT, NEW JERSEY, ASSIGNOB TO WESTERN ELECTRIC COMPANY, INCORPORATED, OF NEW YORK, N. Y., A CORPORATION OF NEW YORK COIL Application filed November 10, 1928. Serial No. 318,380.

This invention relates to electromagnetic devices and more particularly to repeating coils for telephone systems.

An object of the invention is to increase the v range of current density over which a transformer is highly effective.

A more particular object is to improve the effectiveness of long transmission lines which include transformers for transmitting alternating currents.

For example, a certain type of telephone system, which may have its eifectiveness increased by the use of repeating coils in accordance with the invention, employs for 16 ringing purposes alternating currents of about 16% or 20 cycles per second. The

E. M. F. of this .frequency impressed upon a given line is in the neighborhood of 100 volts. The E. M. F. upon the primary terminals of ID the first repeating coil may be, for example,

in the neighborhood of 80 volts. The 20 cycle current is greatly'attenuated due to the line resistance, and the E. M. F. across the terminals of a second repeating coil connected to the first by a relatively long line may be, for example, in the neighborhood of 10 or 20 volts. A coil which'for a call in one direction may be transmitting will for a call in the other directi n be receiving. With re peating coils as heretofore constructed their effectiveness is relatively'high for transmitting impressed voltages in a medium range of 20 to volts but their effectiveness falls off above and below this range. It therefore occurs, in the case of a relatively long line connected to two terminal lines by means of repeating coils, that neither of the coils is worked with a high degree of eflectiveness;

Any means which would increase the effectiveness of such repeating coils at relatively low applied voltages, or at relatively high applied voltages, or at both high and low voltages would improve their operation and the Operation of systems in which they are employed. The benefits of the improvement are realized on the longer lines where the need for themis greatest.

By using in the repeating coil cores two suitably selected magnetic materials in parallel an improvement may be effected. A

transformer having such a core, when properly designed. will have the range of its effectiveness increased. In particular, the efficiency at low and high current densities may be improved.

Others have heretofore experimented with magnetic cores composed of two materials in parallel but it is not thought that any one has recognized any utility in such devices for improving the practical arts or that anybody has proposed to apply two or more materials in cores of coils for useful purposes. So far as known, any such prior investigations have had a purely scientific basis.

The present invention is more particularly disclosed in connection with the accompanying drawings in which:

Fig. 1 represents, in a diagrammatic manner, a repeating coil having primary and secondary windings, the core of the coil consisting of alternate layers or laminations of silicon steel and high permeability nickel-iron alloy commonly known as permalloy, and

Fig. 2 comprises graphs indicating, in a relative manner, the improvement which may be effected by means of such a coil as shown in Fig. 1.

In compiling the data for the graphs of Fig. 2 a 20 cycle current was impressed upon the primary winding of each of several repeating coils and the effective impedances for various E. M. F.s of the current noted. The impedances are plotted in ohmsXlO. It is well-known that the effectiveness of such a repeating coil for a particular low frequency is reduced substantially proportionally to the reduction in impedance at a particular value of current.

Curve A indicates the impedance or effectiveness at various applied voltages of a commercial type of coil with a core of Norway iron. It will be seen that the efiiciency curve is fairly flat and fairly high at to volts but falls off to a low value at 10 to 20 volts. I

Curve B relates to a coil having a silicon steel core. From 10 to 20 volts impressed E. M. F. the values are higher than in the case of nickel-iron but from 55 volts upward the impedance and hence the effectiveness is heat treated to have high permeability at low magnetizing forces.

This coil had increased effectiveness at low voltages but the effectiveness fell ofi' very rapidly above volts.

Curve E relates to such a coil as is illustrated in Fig. 1. In this case the core consisted of alternate laminations of silicon steel 1, (see Fig. 1) and of a high permeability nickel-iron alloy 2 of a composition not exactly determined but somewhere in the neighborhood of to nickel and the balance iron. It will be seen that there is a peak in the impedance or effectiveness curve at around 7 volts, also that the impedance and hence the effectiveness is relatively high and relatively uniform over a wide range, and that in the voltage range between 60 and 85 volts the curve lies above all the others. The improvement depends, in part, at least, upon the fact that the .materials have their maximum permeabilities in widely different ranges of magnetizing force.

Composite cores of other properly selected materials may also be useful. For example, a combination of Norway iron and high permeability nickel-iron alloy has been proposed as well as a combination of silicon steel and Norway iron.

A recently developed magnetic alloy comprising about 50% iron and 50% cobalt when properly heat treated has a very high permeability in a range of magnetizing forces from 5 to 75 gauss. Another, in carrying the present invention into effect, has proposed the use of alternate layers of such a composition with silicon steel or with a nickel-iron alloy heat treated to have very high permeability in a low range of magnetizing forces. Those nickel-iron alloys having around 78 nickel are very suitable for this purpose while'others having between 45% and 85% nickel serve quite well. A combination of cobalt-iron, high permeability nickel-iron, and high permeability nickel-ironwith chromium added is also within the scope of the invention.

The invention is not restricted in its application to repeating coils but may be applied usefully to other transformers and other electromagnetic devices in which it is desired to increase the range of E. M. F. or current density for which the devices are highly eifective. For example, it will be obvious from curve E of Fig. 2 that a choke coil having a core in accordance with Fig. 1

ing of substantially continuous parallel sections of a nickel-iron alloy of 45 to 85% nickel and silicon steel.

In witness whereof, I hereunto subscribe my name this 8th day of November, 1928.

WILLIAM L. CASPER.

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