| 摘要 |
PURPOSE: An apparatus for detecting sample signal of an impedance fault relay is provided to synchronize a zero cross point and sampling timing input to the relay to obtain sample data of constant one period and prevent the error operation of a system, thereby enhancing the stability of the system. CONSTITUTION: A band pass filter(11) removes unnecessary harmonic components of N-phase current. A sample/holder(13) receives the outputs of an amp(12) for holding sampling points. An adder(14) shifts the output level of the sample/holder(13). The first clamper(15) clamps the outputs of the adder(14). A low band pass filter(16) removes unnecessary higher harmonic components of N-phase current. A zero cross point detector(17) receives the outputs of the low band pass filter(16) to detect a zero cross point. The second clamper(18) clamps the outputs of the zero cross point detector(17). A microprocessor(19) receives the outputs of the first clamper(15) as a sample signal of one period in accordance with the outputs of the second clamper(18).
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