GB434030A - Improvements in current transformers - Google Patents

Abstract

434,030. Current transformers. STEIN, G., 34, Tabbertstrasse, Obersch÷neweide, Berlin. March 9, 1934. Nos. 7490/34 and820/35. [Class 38 (ii)] Relates to a current transformer having two or more core sections in which to effect correction of phase angle and ratio errors premagnetization is effected by means of cross-connected windings nb, Fig. 4, supplied from the main secondary n. To effect ratio compensation the voltage applied to the premagnetizing windings nb is maintained constant by means of a parallel connected saturated choke nc. This choke winding may be mounted on a core, as shown, which links the primary circuit. To avoid error due to ohmic drop due to the secondary load current passing through the choke winding, the windings nb may be supplied from a winding inductively coupled with the choke winding. To enable phase angle correction to be effected a resistance R1, Fig. 7, and if desired a resistance R2 may be connected in parallel and series respectively with the windings nb. The resistance R2 may be a barretter type resistance. Phase control may also be effected by a choke connected in series with the main load L. The phase and ratio control may be combined in a single transformer to give combined correction. Further correction may be effected by varying the ratio of core cross-sections. An arrangement is described in which the ratio of cross-section is varied with the turns ratio. Fig. 13 shows an arrangement for obtaining finer correction, in which two auxiliary cores Se are provided, windings nd, and ne in series and parallel respectively with the load L linking these cores. One of these windings may be omitted if complete accuracy is not essential. In a further modification the winding nd is omitted and the winding ne is connected in parallel with the main secondary winding n. Specifications 286,431, [Class 38 (ii)], and 399,611 are referred to.