Air-core dry-type shunt reactor protection based on an alternative current alpha plane

Abstract

This paper proposes an alternative current alpha plane protection for shunt reactors, which is able to identify internal faults, including turn-to-turn faults. The proposed algorithm is based only on zero sequence and neutral currents, eliminating the need for voltage measurements. Furthermore, the proposed algorithm is based on an alternative current alpha plane, where the restraint characteristic is defined simply as its left half-plane, in such a way that minimal settings are required. In order to evaluate the performance of the proposed algorithm, the Alternative Transients Program was used to simulate different internal faults into an air-core dry-type shunt reactor connected to a 230 kV/60 Hz transmission line. The proposed algorithm performance was compared with the restricted earth fault function. From the obtained results, it is demonstrated that the proposed protection properly operates in turn-to-ground and turn-to-turn faults with operation times shorter than one power cycle, even for 1% of short-circuited turns. On the other hand, restricted earth fault function failed to operate in some of these cases. The proposed algorithm ensured the integrity of the air-core dry-type shunt reactors in all evaluated scenarios, correctly restraining in all simulated external faults (including cases with current transformer saturation). Thus, the proposed algorithm is considered a reliable and promising alternative for shunt reactors protection.