Power transformer protection scheme based on time-frequency analysis

Abstract

SUMMARY This article presents a new approach for power transformer protection based on a hybrid pattern recognition scheme. The hyperbolic S‐transform (HST) is a very powerful tool for analysis of the nonstationary waveforms because it is able to extract the information from transient signals simultaneously in both time and frequency domains. Magnitude, frequency, and HST contours are the main attributes obtained from the output matrix of HST. At first, differential current waveforms of different conditions such as normal, internal and external faults, inrush, and over‐excitation conditions are analyzed by HST and some potential useful features are extracted from the abovementioned contours. To decrease the dimension of feature vector and to increase the classification accuracy of the proposed algorithm, the most effective features are selected by using well‐known feature selection methods namely sequential forward selection, sequential backward selection, and genetic algorithm. Selected features are trained by a probabilistic neural network as an effective classifier core, which has advantages regarding learning speed and generalization capability compared with feed‐forward neural network. The classification accuracy of the proposed algorithm has been used as a criterion function for the selection of the best subset features. The proposed protection scheme is evaluated for various operating conditions of three different transformers using the PSCAD/EMTDC package. Extensive simulation results show that the proposed algorithm relies only on the waveshape properties, and it is independent of the value of transformer parameters and consumed power. Copyright © 2012 John Wiley & Sons, Ltd.

A new model to study ultra-saturation phenomenon during the energization of a loaded three-phase power transformer and its effects on differential protection

“…So, the standard differential protection is not able to identify the ultra-saturation phenomenon, and the description and control of the ultra-saturation phenomenon is necessary for preventing the false trip of the differential protection. Also, several studies have been carried out to distinguish between the inrush current and the internal and external faults by various algorithms [8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23], but none has taken the ultra-saturation phenomenon into account. This paper presents a new model for investigating the ultra-saturation phenomenon during energization of a loaded three-phase power transformer.…”

“…Several studies have been carried out to distinguish internal faults from external faults and the magnetic inrush current by various algorithms such as the harmonic restraint and the park transform . Also, some works have used special algorithms such as the support vector machine‐based protection scheme , the self‐adaptive transformer differential protection , the time‐domain analysis of differential power signal , the inner bridge connection , the standard 87T differential protection for power transformer and special power transformer , intelligent hybrid systems , moving windows , S‐transform , time‐frequency analysis , differential evolution , negative sequence analysis , and S‐transform and fuzzy expert systems to distinguish between the transient phenomena. But none of these studies have modeled the ultra‐saturation phenomenon.…”

Development of an adaptive differential protection scheme for transformer during current transformer saturation and over‐fluxing condition

“…However, the above works do not include cases such as over-fluxing conditions to avoid false operation of the transformer protective scheme. A classifier method employing a combination of hyperbolic S-transform (HST) and probabilistic neural network (PNN) 6 and another involving S-transform and the hidden Markov model (HMM) 7 have been elaborated. These classifier methods are able to classify various types of faults but, unfortunately, they may misclassify momentary over-fluxing conditions.…”

The effect of transformer non-synchronous energization on differential protection and its countermeasure

“…Differential protection is usually adopted as the main protection of power transformers. To increase the reliability of the transformer differential protection, much improvement has been achieved on the detection of inrush current [1][2][3][4][5][6][7][8]. However, mal-operation caused by the inrush current still has been recognized as one of the key issues in transformer differential protection.…”