On the Problem of Selecting and Replacing Current Transformers for Relay Protection Devices

Abstract

In connection with cases of incorrect operation of high-speed relay protection devices (RPD) in case of short circuits outside their range, the issue of replacing current transformers (CT) of class P with more advanced current converters is relevant. The article shows that the decision to replace existing class P CTs with CTs with a non-magnetic gap should be made taking into account the probability of saturation of the magnetic cores of the latter in a transient short-circuit mode, as well as an increase in their dimensions compared to class P CTs. The issue of using optoelectronic current converters should be resolved after the latter are put into mass production, taking into account the difficulty of integrating the latter with the RPDs implemented using an Electromechanical base. In many cases, the correct functioning of high-speed RPDs without replacing existing CTs of class P can provide the following measures: the use of algorithms that increase the stability of the operation of high-speed RPDs when the CT is saturated; taking into account in the calculations of the settings the rectangular characteristic of the CT magnetization in transient modes and the permissible deceleration of protections under the condition of the dynamic stability of electric power systems; refusal to use CT connection groups (physical sum of currents, delta and star).