Stator grounding protection with combined third harmonic dynamic alignment criterion and voltage ratio criterion

Abstract

This invention disclose a method for discriminating the earth fault of generator stator windings by distinguishing neutral point voltage triple harmonic component and that of the generate end open-end triangle voltage including the following steps: a protection device samples the voltage waveform of the voltage mutual inductor to get a transient value, evaluating the complex, form of the triple-harmonic voltage by Fourier algorithm plus digital filter algorithm, computing out its varied volume and its potential, automatically entering into the improved dynamic regulation of its voltage differential criteria under heavy load, automatically entering into its voltage ratio criteria under light load before interconnection, protection is operated after a delay when aided criteria meet the needs simultaneously.

Description

technical field [0001] The present invention relates to the field of power systems, and more particularly to a method for relay protection. Background technique [0002] Large-scale synchronous generator sets are the basic equipment for electric energy production and occupy a very important position in the power system. In recent years, the single unit capacity of generators has been continuously increasing. They are extremely expensive and have a more complex structure. Once they are damaged due to faults, maintenance is difficult and takes a long time. At the same time, it will affect the stability of the system and cause direct and indirect damage to the national economy. The loss was enormous. In this way, higher requirements are put forward for the selectivity, rapidity, reliability and sensitivity of the unit protection device. [0003] Stator winding single-phase ground fault is one of the most common faults of generators, and it is often the precursor of more serio...

AI Technical Summary

Problems solved by technology

In practice, the operation of the fundamental wave zero-voltage stator grounding protection is good, but the field operation of the third harmonic stator grounding protection is poor. The main reason is that the content of the third harmonic is relatively small during normal operation. The design of the filtering algorithm brings a series of problems, coupled with the abnormality of the on-site zero-sequence voltage transformer (referred to as TV, the same below) circuit and the protection implementation method is not perfect, making the third harmonic stator grounding protection a very easy misoperation protection, seriously affecting the safe and stable operation of the generator

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