Relay protection method for single-phase grounding of cable terminal of ungrounded system

Abstract

The invention discloses a relay protection method for single-phase grounding of a cable terminal of an ungrounded system. The relay protection method comprises the following steps: acquiring zero-sequence power P1 flowing through a three-phase current transformer of a feeder line; obtaining the zero sequence power P2 flowing through the feeder zero sequence current transformer; obtaining zero-sequence power P1 flowing through a feeder line three-phase current transformer; acquiring zero-sequence power P2 of a zero-sequence current transformer flowing through a feeder line; when the zero-sequence power P1 flowing through the feeder line three-phase current transformer is larger than 0, the zero-sequence power P2 flowing through the feeder line zero-sequence current transformer is smaller than 0, and the difference value Pc between the zero-sequence power P1 flowing through the feeder line three-phase current transformer and the zero-sequence power P2 flowing through the feeder line zero-sequence current transformer is larger than a zero-sequence power difference threshold value Pd, it is considered that the cable end single-phase earth fault occurs; if yes, the faulty cable breaker is tripped off after time delay t, otherwise, it is considered that the cable end single-phase earth fault does not occur, and the method can accurately judge the cable end single-phase earth fault and remove the fault in time.

Description

technical field [0001] The invention belongs to the technical field of power system relay protection, and in particular relates to a relay protection method for single-phase grounding of cable terminals in an ungrounded system. Background technique [0002] With the increasing application of cables in power supply and distribution systems with voltage levels of 6kV to 35kV, the probability of cable faults has gradually increased, among which single-phase ground faults at the cable ends account for a higher proportion. The single-phase grounding fault at the end of the cable often leads to the phase-to-phase fault at the end of the cable, which expands the scope of the accident. For 6kV to 35kV ungrounded power supply and distribution systems, the fault current is the system capacitance current when single-phase grounding. At present, wire selectors are mostly used to find single-phase grounding faults. [0003] The cable terminal is located between the external zero-sequenc...

AI Technical Summary

Problems solved by technology

[0003] The cable terminal is located between the external zero-sequence current transformer and the feeder circuit breaker. If a single-phase ground fault occurs at the cable terminal, the line selector based on the ground fault current of the zero-sequence current transformer will judge that it belongs to an external fault protection and will not act. , the fault cannot be effectively removed, endangering the safety of power supply and distribution, that is, the single-phase ground fault at the end of the cable cannot be accurately identified, so the fault cannot be removed in a timely and effective manner

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