When the transformer is closed at no load,the zero-mode inrush current will be generated,and the in-rush amplitude is high and lasts for a long time,which may cause the malfunction of the zero-sequence overcur-rent protection,which is more serious in the case of a large number of high-impedance transformers(HIT),and it needs to be equipped with a suitable locking scheme.Given this,this paper designs a zero-mode inrush cur-rent identification and protection lock-up criterion based on the Frechet distance algorithm,and uses the advan-tages of Frechet distance to satisfy trigonometric inequality and waveform analysis diversification,and identifies the zero-mode inrush current by calculating the Frechet distance value of the adjacent period of the zero-mode inrush waveform and setting the threshold,which makes up for the problem that the methods such as second-harmonic braking cannot effectively identify the zero-mode inrush current in the case of no-load closing.The simulation results show that the proposed criterion can effectively identify the zero-mode inrush current and has strong anti-interference ability.
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