| 摘要 |
PURPOSE: A digital protective relay is provided to selectively operate two current transformers according to a current level of a zero-phase current signal inputted from a zero-phase current transformer installed in a distribution line, thereby preventing malfunction. CONSTITUTION: A first current transformer(111) and a second current transformer(113) are serially connected each other, and an identical zero-phase current signal is flowed in a first coil side of the first and second current transformers. A current level for normal operation of the first and second current transformers is differently set. The first current transformer transforms a zero-phase current signal in a predetermined ratio and outputs a first zero-phase current signal. The second current transformer transforms the zero-phase current signal and outputs a second zero-phase current signal. A control unit(120) selectively operates the first and second current transformers according to the current level of the zero-phase current signal. The control unit operates a relaying element based on the first zero-phase current signal or the second zero-phase current signal, the zero-phase current signal, and a phase difference of the first zero-phase current signal or the second zero-phase current signal and the zero-phase current signal.
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