Earthing protection method for small current earthing system

Abstract

The earthing protection method includes the steps of: to monitor the zero-sequence voltage of the system and the negative-sequence current of feeders and optionally monitor phase voltage and the zero-sequence current of feeders; to judge systemic fault in case of zero-sequence voltage greater than the synchronized value; to calculate the change amount in negative-sequence current of feeders after fault; and to judge line fault based on the magnitude, direction or energy function of the negative-sequence current in case of the change amount of negative-sequence current in some feeder greater than precise working curret. The method raise the protection reliability and precision, may realize sectional judgment, is easy to realize in FTU and can meet the requiremen for automatic power distribution.

Description

technical field [0001] The invention relates to the relay protection technology of electric power system, especially the single-phase grounding line selection and protection of the neutral point not directly grounding system. Background technique [0002] The neutral point non-direct grounding system is referred to as the small current grounding system. When a single-phase grounding fault occurs, an overvoltage will be generated. If it is not cleared in time, it may cause cable explosion and other faults, affecting the safety and power quality of the power system. At present, the distribution network generally adopts one by one tentative switch to find the faulty line, which cannot meet the requirements of the development of the power system. Application No. 91103633 titled "Detection Method and Device for Small Current Grounding" discloses a method for comparing the magnitude of the AC harmonics of the zero-sequence current in each outgoing line in the power grid, and the o...

AI Technical Summary

Problems solved by technology

Since the ground fault current is affected by the system compensation degree and grounding resistance, the size and direction are uncertain, and the relationship between the zero-sequence current of the fault line and the zero-sequence current of the non-fault line is also affected by the system compensation degree and operation mode, and the change is uncertain. The reliability of zero-sequence current fault line selection is not high: while the zero-sequence harmonic current is affected by various random factors such as the saturation degree of the transformer and the load, it is difficult to set the grounding protection with zero-sequence harmonic current, and the reliability is not high; The comparison of zero-sequence harmonic and reactive power is greatly affected by system parameters and has high requirements for measuring devices. It is difficult to realize the comparison of the measured quantities of each outgoing line by the existing methods on the field terminal unit FTU of the switch on the distribution automation column. Conducive to the application in distribution automation

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