Patent GB-310766-A (GB)
Title: Electric alternating current measuring instruments
IPC: G01R11/00
Filed: 1928-01-26
Abstract: 310,766. Nalder Bros. & Thompson, Ltd., and Lipman, C. L. Jan. 26, 1928. Current and power meters; frequency, inductance, and resistance, measuring.-Relates to alternating- current induction type measuring instruments in which the driving fluxes are obtained by a main flux, and a displaced flux which is produced by auxiliary windings on a stationary core part, or on auxiliary polar projections of the main magnet core, the fluxes due to the auxiliary windings being confined to paths which, while interacting with the main flux, do not mutually intersect and act in the same or in opposite directions on the moving system. The instruments are compensated for changes of frequency and temperature. In one arrangement, Fig. 1 (Prov.), the poles C', C<2> of an ammeter or voltmeter are angularly displaced and the auxiliary windings Q<1>, Q<2> are wound on the projections g<1>, g<2> of a stationary core within a rotatable cylinder D. The time phase between the main and auxiliary fluxes may be adjusted by a resistance or impedance x. In modifications, the windings Q<1>, Q<2> are fed from a secondary winding, and instead of the cylinder D, two coaxial discs are driven, or a single disc can be employed, the auxiliary fluxes traversing diagonally opposite parts of the iron system. Where two dials are provided the scale readings are in the same direction. A differential frequency meter, Fig. 6 (Prov.) comprises auxiliary windings Q<1>, Q<2>, competed in parallel and having either an inductive or non-inductive resistance L', R', in circuit, an inductance L being provided in the primary circuit P as a filter. In a modification, the parallel-connected auxiliary circuits are in series with the primary winding and a permanent magnet brake is provided. The rotatable drums are perforated to reduce their mass and enable them to give stable readings without the use of control springs. A unidirectional differential current instrument with a frequency bias in both directions, Fig. 8 (Prov.), comprises primary windings P, P' and a secondary winding S feeding the parallelconnected auxiliary windings Q<1>, Q<2> which have respectively in circuit a resistance R<1> and condenser K. At normal frequency the ampereturns of the winding Q<1> are greater than those of the winding Q<2>, a change in frequency acting in opposite directions in the differentially-connected coils Q<1>, Q<2>. In modifications, the rotor comprises one or two discs, the auxiliary winding being located on polar projections of the main core. Fig. 12 (Prov.), shows a duodirectional differential current or voltage instrument, the primary coils P<1>, P<2>, being connected in series respectively with auxiliary coils Q<1>, Q<2>. Other modifications of duo-directional instruments compensated for temperature and frequency changes are described.. Fig. 16 (Prov.), shows a wattmeter, P being the pressure coil and Q<1>, Q<2>, the current coils. Shortcircuit coils F in series with a resistance R<2> provide power-factor compensation. Further wattmeter constructions are described having duo-directional features and the usual compensations, Fig. 22 (Prov.), shows a duo-directional double-disc ammeter or voltmeter having secondary windings S on a readily saturated core and connected to auxiliary windings V<1> - - V<4> on polar projections Z<1> - - Z<4>. Fig. 1 (Comp.), shows a portable multirange ammeter or voltmeter having a removable yoke B on which is located a variable primary winding P. Fig. 2 (Comp.), shows a portable leakage indicator in which the primary winding comprises a three-phase cable P, a measurement of the out-of-balance current being given by pointer a on a scale b which is open at lower current readings, Fig. 4 (Comp.), shows an instrument for measuring impedance components, Q<3>, Q', being main current windings and Q<1>, Q<2> auxiliary current windings connected in series therewith and shunted by a resistance R. These windings are connected to a current transformer (not shown), the winding P comprising the voltage element. The instrument measures V cos #/I or V sin #/I and in the former case may measure the distance of a fault. In a modification, the coil P in series with winding Q<1> on a cruciform core form the current element, and the winding Q<2> in series with tapped impedances provides the voltage element. In a further modification, the total impedance or the impedance ratio is measured on a double element instrument, the current and voltage magnet systems rotating the mechanically coupled rotor in opposite directions. Rotors for use with the instruments described are constructed with portions of the top surfaces provided with apertures or with inserts of magnetic material, two forms being shown in Figs. 23, 26 (Prov.). Specification 294,919 is referred to.