A New High Accuracy Current Transformer

Abstract

This paper is presented for the purpose of describing a new method of compensation, by the use of which the ratio and phase-angle errors of current transformers are materially reduced. There are several methods by which the ratio and phase-angle errors of current transformers may be reduced. The following are those which are most commonly used: 1. By changing the number of secondary turns, which reduces ratio errors only. This method is universally used and operates satisfactorily under various conditions of burden, frequency, etc. 2. By the use of a larger number of ampere-turns, a large cross-section of core, or both. An increase in either one of these factors improves the accuracy characteristics of the transformer under the different conditions of burden, frequency, or secondary current. 3. By the use of a high-permeability low-loss steel, which improves the transformer characteristics for moderate values of secondary burdens. The errors increase rapidly under overload conditions. 4. By the use of the two-stage type transformer, which operates satisfactorily under the various conditions of burden and frequency. Slightly special equipment is required, however, for power or energy measurements. 5. By the use of compensating shunts across the primary or secondary windings of the transformer. This method operates satisfactorily only under fixed conditions of burden, frequency, etc. 6. By a new method, in which the secondary turns enclose a section of the magnetic circuit and a short-circuited band encircles the same section.