Negative-sequence time-overcurrent relay

摘要

Disclosed is a negative-sequence time-overcurrent relay for use in a polyphase synchronous rotary electric machine (1) having a main-circuit breaker (3) and an exciting circuit (1B). The negative-sequence time-overcurrent relay comprises first extracting unit (5, 7, 8, 11) for extracting a fundamental-wave component and a harmonic component from a predetermined electric parameter for each phase given to the polyphase synchronous rotary electric machine (1), second extracting unit (9) for extracting a fundamental-wave negative sequence current for each phase from a fundamental wave for each phase extracted from the first extracting unit (5, 7, 8, 11), first calculating unit (10) for squaring the fundamental-wave negative sequence current for each phase, extracted by the second extracting unit (9), for each phase, second calculating unit (12) for squaring the harmonic component for each phase, extracted by the first extracting unit (5, 7, 8, 11), for each phase, first adding unit (13) for adding phase-by-phase operational outputs from the second calculating unit (12), multiplying unit (14) for multiplying an output from the first adding unit (13) by a predetermined constant, second adding unit (15) for adding a phase-by-phase output from the second calculating unit (12) to an output from the multiplying unit (14), and determining unit (16) for determining that the polyphase synchronous rotary electric machine is protected when a sum of added values for individual phases obtained from the second adding unit (15) exceeds a predetermined value.