A digital scheme to minimize the influence of transformer magnetizing inrush or CT saturation on line protection

Abstract For transformer magnetizing inrush or current transformer (CT) saturation, conventional blocking techniques result in interruption or severe delayed operation of protective relays. Besides, the reliability of CT saturation blocking (or compensation/reconstruction) techniques may be also disturbed by transformer magnetizing inrush. For improvement, this paper proposes a digital waveform reconstruction scheme, instead of blocking techniques, to eliminate distorted portions caused by magnetizing inrush or CT saturation from current signals, which minimizes the adverse effects on line protection. Concretely, the proposed scheme implements the portion segmentation, distortion portion identification, distortion portion elimination, and waveform reconstruction, according to calculated real time amplitude and ratio of boundary gradient. Case test results indicate the correctness and effectiveness of the proposed scheme. It is able to repair the waveform of CT saturation current. Moreover, it opens a new door to eliminate magnetizing inrush component from current signals in power lines. The reconstructed current waveform without distortion is outputted in real time, which contributes to the uninterrupted correct operation of protective relays in power lines.

[1]  Carlos A. Duque,et al.  Current-Transformer Saturation Detection Using Savitzky-Golay Filter , 2016, IEEE Transactions on Power Delivery.

[2]  Hong-Jun Yoon,et al.  Correction of current transformer distorted secondary currents due to saturation using artificial neural networks , 2001 .

[3]  Ivo Uglešić,et al.  Simulation of three-phase transformer inrush currents by using backward and numerical differentiation formulae , 2015 .

[4]  Larry Wright,et al.  Mitigation of Undesired Operation of Recloser Controls Due to Distribution Line Inrush , 2017, IEEE Transactions on Industry Applications.

[5]  Mehdi Vakilian,et al.  Current-Transformer Saturation Compensation for Transformer Differential Relays , 2015, IEEE Transactions on Power Delivery.

[6]  Sy-Ruen Huang,et al.  Distinguishing Internal Winding Faults From Inrush Currents in Power Transformers Using Jiles-Atherton Model Parameters Based on Correlation Coefficient , 2012, IEEE Transactions on Power Delivery.

[7]  Haidar Samet,et al.  Efficient method for discrimination between inrush current and internal faults in power transformers based on the non-saturation zone , 2017 .

[8]  M.S. Sachdev,et al.  A New Algorithm for Digital Impedance Relays , 1979, IEEE Transactions on Power Apparatus and Systems.

[9]  B. R. Bhalja,et al.  Discrimination Between Internal Faults and Other Disturbances in Transformer Using the Support Vector Machine-Based Protection Scheme , 2013, IEEE Transactions on Power Delivery.

[10]  Jie Tian,et al.  A novel error compensation algorithm for three-current transformer connection , 2010 .

[11]  Ubiratan Holanda Bezerra,et al.  A method to identify inrush currents in power transformers protection based on the differential current gradient , 2014 .

[12]  Ali Hooshyar,et al.  CT Saturation Detection Based on Waveform Analysis Using a Variable-Length Window , 2011, IEEE Transactions on Power Delivery.

[13]  Hamid Lesani,et al.  Discriminating transformer large inrush currents from fault currents , 2016 .

[14]  M. Banejad,et al.  A correlation based method for discrimination between inrush and short circuit currents in differential protection of power transformer using Discrete Wavelet Transform: Theory, simulation and experimental validation , 2013 .

[15]  Qinghua Wu,et al.  Using mathematical morphology to discriminate between internal fault and inrush current of transformers , 2016 .

[16]  M. Davarpanah,et al.  Compensation of the Current-Transformer Saturation Effects for Digital Relays , 2011, IEEE Transactions on Power Delivery.

[17]  Teymoor Ghanbari,et al.  Discrimination of internal fault from magnetising inrush current in power transformers based on sine-wave least-squares curve fitting method , 2015 .

[19]  Pei Liu,et al.  A series multiresolution morphological gradient-based criterion to identify CT saturation , 2006 .