Transient Protection Principle Based on Current Ratio of Two Terminals in Frequency Domain

Abstract

In order to prevent a transmission line boundary having a weak high frequency from impairing single-ended transient-based relay protection, this paper proposes using the coordination of the current frequency domain features of the relay on both sides of the transmission line to achieve whole-line quick-action protection. In the case of an internal fault, since the frequency components of the electrical quantities in the frequency domain on both sides of the protected line are related to the distance from the fault point to two sides of the line, the frequency-domain current spectrum information on both sides of the line is very different and the fluctuation is strong. In the case of an external fault, the transient current at the protection point closer to the fault is transmitted through the entire length of the protected line and reaches the other side away from the fault. Therefore, the fluctuation in the current spectrum in the frequency domain on both sides is quite different. Thus, this paper proposes setting the fault criterion according to the difference in the frequency spectrum fluctuation degree of the frequency-domain current ratio on both sides when internal and external faults occur. After verification using PSCAD simulation, it was found that the protection principle proposed in this article can act quickly and correctly, and identify internal and external faults, under different fault types and fault locations, and is basically not affected by transition resistance.