GB531127A - Improvements in and relating to electric current measuring devices - Google Patents

Abstract

531,127. Current measurements. AKT.- GES. BROWN, BOVERI, & CIE. July 12,1939, No. 20326. Convention date, July 13, 1938. [Class 37] A conductor a carrying a continuous current to be measured is surrounded by an iron core b carrying a winding l through which flows a continuous current which is automatically varied so as to produce a magneto-motive force opposing that produced by the current in the conductor a, the value of the compensating current being measured by an ammeter A. The core b has a bridge c and is provided with air gaps o. Pivoted between the poles N, S of the core b is an armature e, Fig. 1, which may be polarized by a D.C. winding k. This armature varies a resistance f in series with the coils l and takes up an equilibrium position in which the magneto-motive forces due to the current in the conductor a and that in the coils l are balanced. The resistance f may be of the rolling- sector type shown or of the carbon compression type. The continuous current supplying the coils l and the polarizing winding k may be taken from an A.C. circuit h through a transformer t and rectifier g. In order to prevent sudden changes of flux in the core b due to sudden changes in the current in the conductor a, short-circuited coils may be provided on the core, or a solid iron core may be used. In a modification, Fig. 2, a discharge tube E having one or more anodes is arranged between the poles of the core b so as to be magnetically influenced thereby, and serves both as a rectifier and as an automatic regulator for the current in the coils l. Short-circuit rings s are provided on the core.