Recognition Of The Power Transformer Magnetizing Inrush Based On S Transform

With the development of the power system, optimization of the power source,long-distance high-voltage transmission than before has been a large-scale, large-areaapplications. Power system voltage levels have also been improved leaply, operation ofthe power system security becomes ever important, so requirements for relay protectionbecome abnormal strict. As far as we know, power transformer protection is the weakestlink in the power system relay protection, The main factors affecting the transformerdifferential protection is to identify inrush current and fault currents.This paper analyzes the operating characteristics of the transformer, the principleof relay protection. On this basis, I build a simulation model of the transformer underideal conditions and when current transformer is saturated as well as suffering fromharmonic interference for load switching, single-phase ground fault, two-phase shortcircuit fault, two phase to ground fault, three-phase short circuit fault.Analyzing transformer magnetizing inrush and internal fault current takesadvantage of time-frequency analysis capabilities of generalized S transform. Creating astandard frequency mode matrix by generalized S transform gets the characteristic ofthe current. Getting the information entropy of the amplitude and frequency by usinginformation entropy to quantify fault feature recognizes the magnetizing inrush and thefault current.Papers discuss the identification between the magnetizing inrush and the faultcurrent under ideal conditions and when current transformer is saturated as well assuffering from harmonic interference in depth. Papers study problem about selection ofthe amplitude information entropy and frequency information entropy. Giving thethreshold of the amplitude information entropy and the threshold of the frequencyinformation entropy identifies the magnetizing inrush and fault current. According to alarge number of simulations, if amplitude information entropy of the current is less thanthe threshold of amplitude information entropy the current was magnetizing inrush under ideal conditions. Meanwhile, if frequency information entropy is more than thethreshold of frequency information entropy the current was magnetizing inrush underideal conditions. We can only judge the current through the frequency entropy when thecurrent transformer is saturated. We also could only judge the current through theamplitude entropy when the current suffer form the harmonic interference. Therefore,with comparing the information entropy and the threshold, as long as at least onejudgment established to the recognizer, the current is magnetizing inrush.