Determination of the Time-to-Saturation of Current Transformers in Short-Circuit Transient Regimes

Abstract

The existing methods of calculating the time-to-saturation of CT are analyzed. Since cases of core saturation have been observed in class P CT with high primary current multiples for which incorrect actions of the relay protection devices occurred in short-circuit transient regimes, in the proposed standard GOST R “Measuring transformers: Part 2. Requirements of current transformers” the coefficient of the transient regime and the time-to-saturation of CT are introduced as characteristics of CT. Amethod developed by the present authors is proposed for calculating the indicated time. Conclusions are drawn about the applicability of the methods in practical calculations. The calculation of the time-to-saturation of CT installed in 500 kV outdoor switchgear in a large electric power plant is presented as an example.