Operation of Relay Protection Digital Elements at Saturation of Current Transformers: Modeling and Analysis

The paper is devoted to modeling and analyzing the operation of digital elements (DE) of relay protection at saturation of instrument current transformers (ICT). It reviews the algorithms for DE based on calculations from instantaneous signal values and using Fourier filters. The secondary current values at saturation were obtained by modeling in the Matlab program using a simplified mathematical CT model. We studied the influence of such factors as the sample time and the damping decrement of the aperiodic component of the input signal on the accuracy of the DE operation. The obtained results from modeling were justified. It was found that the nature of the change in errors is different for algorithms based on instantaneous values of signals, and for those based on Fourier filters. By increasing the damping decrement, the absolute errors decrease. When switching devices to the IEC 61850-9-2 data communication protocol, it is preferable to use an algorithm of two samples or DE based on Fourier filters.