| 摘要 |
PROBLEM TO BE SOLVED: To solve the problem that a low level zero phase voltage accident is hard to detect when deciding the direction of the ground fault current by comparing the phase of the zero phase voltage and the zero phase current. SOLUTION: Phase voltage detectors to the ground 1R, 1S, 1T detect the voltages for respective phases. A zero phase current transformer 2 detects the zero phase current of the distribution line. A ground fault direction relay 3 detects the phase voltage and using it as the reference decides the direction of the ground fault current by comparing the phase of the zero phase current detected by the zero phase current transformer and this reference voltage. When the ground fault accident is not serious, the direction is decided on the basis of the voltage to the ground, but when the accident becomes larger with the increasing zero phase voltage, the phase of the zero phase current is also compared using the zero phase voltage obtained putting together each voltage as the standard. Besides, the phase voltage detector also obtains the voltage of the remaining phase after detecting the voltages for the two phases out of the three of the distribution line.
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