Error Evaluation of a Current Transformer, Respect to the Time Constant of the Primary and Secondary Current

Abstract

Due to the characteristics of the electric power systems in a short-circuit, the current transformers CTs can be energized by a current with a d.c. component. Considering this situation, the aim of the present work is to evaluate the error when a CT is used to measure this type of currents in relation with the primary time constant (T_p) and the time constant of the current transformer secondary loop (T_s). In order to evaluate the aforementioned relationship in steady-state and transient conditions, a CT working in linear conditions and a negligible leakage flux is used; this condition is close to the actual operation if its magnetic core does not reach saturation. It is worth mentioning that CT saturation is a situation that, in general, is convenient to avoid, since it may cause a distortion in the secondary current that could cause an incorrect operation in related equipment.