Discrimination of internal fault from magnetising inrush current in power transformers based on sine‐wave least‐squares curve fitting method

Abstract

This study deals with a method for discrimination between magnetising inrush and internal fault currents in three-phase transformers based on sine-wave curve fitting. A sine wave is fitted to the normalised differential current by using the leastsquares technique for each phase. The difference between the normalised differential currents and the fitted signals are calculated, which are hereafter named residual signals (RSs). Maximum range of the RSs variations is utilised for the definition of a simple criterion. Based on this criterion, the discrimination is realised within less than a half cycle of power frequency. In order to eliminate the impact of the current transformer (CT) saturation on the performance of the proposed technique, the currents are compensated by a CT saturation compensation algorithm in the first step. The proposed method is evaluated and compared with some well-known methods by a large number of simulation and experimental data. Furthermore, the proposed algorithm is evaluated in the case of a transformer, which is fed through a feeder with series capacitors. The results confirm that reliability, accuracy and speed response of the proposed technique is more than the other methods.

Identifying internal fault from magnetizing conditions in power transformer using the cascaded implementation of wavelet transform and empirical mode decomposition

“…Plenty of literatures have suggested methods to detect internal fault from inrush currents. As shown in Figure 1, these methods are classified into 7 groups based on the input signals and the procedure of their algorithm as follows: (a) methods that use harmonic components of the differential current, [1][2][3][4] (b) methods based on utilizing the wave shapes of differential current, [5][6][7][8][9][10][11][12] (c) methods based on the flux signals, 13,14 (d) methods based on power calculating, [15][16][17] (e) methods based on voltage and current signals, 18,19 (f) methods based on transformer inductance, 20,21 and (g) methods based on artificial intelligence techniques. [22][23][24][25][26] Abbreviations: Current transformer, (CT); Discrete wavelet transform, (DWT); Empirical mode decomposition, (EMD); Intrinsic mode functions, (IMFs); Fast Fourier transform, (FFT); Low-pass filters, (LPF); High-pass filters, (HPF) Symbols: D n , n'th level detail coefficient; r n , EMD residue signal; IMF n , IMF of level n; X(t), Input signal of EMD method; i diff , Differential current; E IMF;rn , Energy of the IMFs and the residue; E D2 , Energy of D 2 ; i No (n), Normalized differential current in sample n; є 1 , Threshold of criterion 1; є 2 , Threshold of criterion 2…”

IEC61850 standard-based harmonic blocking scheme for power transformers

“…The differential protection uses differential currents, which result from the difference between HV side and LV side currents and overcurrent uses only primary current. Energization of transformers causes inrush current passing through the transformer coils [14].…”

Evaluation of directional relay algorithms in presence of wind turbines and fault current limiters

“…On the other hand, in order to handle the increased fault current, protection equipment such as fuses and breakers should be replaced with higher rating equipment, which is a time consuming and expensive approach. Utilizing fault current limiters (FCLs) is one of the most attractive techniques to overcome these problems . During normal operation of power system, these facilities have negligible effect on the power system.…”

“…Utilizing fault current limiters (FCLs) is one of the most attractive techniques to overcome these problems. [8][9][10][11][12][13][14][15] During normal operation of power system, these facilities have negligible effect on the power system. However, they limit fault current through an impedance when a fault occurs.…”