| 摘要 |
In a line protection unit for monitoring fault conditions of an electrical power line and actuating breakers to disconnect the line from a power supply bus, the supply bus is in the ring bus arrangement including a first bus and an auxiliary bus so that each power line includes first and second breakers. The three phase current in the line is monitored at both the breakers and summed in the unit to allow calculation of the fault conditions based upon the total current in the line. In the event of a fault condition, both breakers are tripped. In the event of breaker failure so that current continues to flow, this is detected in the unit and all the first breakers tripped to prevent the faulty breaker from allowing current to flow to the faulty line.
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