The study of power transformer differential protection’s operation in the internal fault conditions

Abstract

Special attention is paid to high-speed relay protections’ operation in transient modes due to a number of major failure events that have occurred over the past 10 years in the power system of the Russian Federation. Operation of power transformer’s differential protection in case of internal short circuit is studied in this research. False blocking of protection is possible in such mode due to saturation of current transformers. A value of blocking time may exceed the maximum permissible short-circuit disconnection time under conditions of maintaining the dynamic stability of the power system. Primary and secondary currents in transient modes are obtained by simulation of short circuits. Windings of the modeled current transformers are connected in a star to a null wire. RMS values are calculated using a mathematical model of the Fourier filter. The current transformers were checked according to the methods declared in PNST 283-2018 and GOST R 58669-2019. The analysis carried out in this work allows to estimate possibility of long-term blocking of the differential protection of a power transformer in case of internal short circuit, especially in case of significant value of time constants.