| 摘要 |
A differential protective relay for protecting devices on an ac electrical power system. The protected devices can include a transformer, a generator, or a station bus. The differential protective relay evaluates the current flowing into and out of the protected device only during the period when the current transformers are not saturated. The differential protective relay also detects internal faults accompanying external faults by evaluating the ratio between the current flowing into and out of the protective device. When this ratio exceeds a predetermined limit the protective relay evaluates the difference between the current flowing into and out of the device to determine if this difference is sufficiently large to trip the relay. When a current transformer associated with the differential protective relay is saturated, the differential protective relay produces a restraint signal to restrain tripping.
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