| 摘要 |
PROBLEM TO BE SOLVED: To identify a failed line and to enable only the failed line to be interrupted without expanding a power failure range through all-out interruption even on a ground fault failure of a distribution line in the case of a fewer-feeder system or even when only resistance-portion current flows at worst. SOLUTION: A high sensitivity type ground fault direction relay 10B1 operates when AND conditions are satisfied in an A characteristic that enhances a ground fault detection sensitivity which is an operation setting value that prevents the operation with a residual current of a zero-phase current transformer ZCT, a B characteristics that maximizes the ground fault detection sensitivity when a zero-phase current phase is identical to the phase of a zero-phase voltage of a reference voltage, and a C characteristic that delays the zero-phase current phase by 15° from the zero-phase voltage of the reference voltage. A ground fault overvoltage relay 10B2 detects 70% or higher of the rating of the zero-phase voltage. When the AND conditions are satisfied in the ground fault direction relay 10B1 and the ground fault overvoltage relay 10B2, an auxiliary relay 10RY is operated via an OR circuit 10OR. COPYRIGHT: (C)2011,JPO&INPIT
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