The paper presents a new algorithm, its implementation, and results of extensive testing, for a microprocessor-based low-impedance busbar relay. For increased security, the presented technique combines percent differential and current directional protection principles. The directional (phase comparison) principle does not require a voltage signal as it responds to relative directions of the currents. For fast operation, the outlined approach uses an adaptive trip logic that shifts between the 2-out-of-2 operating mode and the differential principle alone depending on a detection of CT saturation. The saturation detector responds to a differential-restraint current trajectory and is capable of detecting saturation occurring as fast as approximately 2 msec into a fault. The presented solution is implemented as a centralized type microprocessor-based relay with a sub-cycle tripping time and exceptional immunity to CT saturation.
Bogdan Kasztenny, Kazik Kuras, In Proc. IEE/PES Summer Meeting 2001, Vancouver Canada, vol.1, pp. 97-102
KEYWORDS: busbars, numerical relaying, adaptive protection, low-impedance differential protection, current transformers, CT saturation detection.