A new algorithm for avoiding maloperation of transformer restricted earth fault protection caused by the transformer magnetizing inrush current and current transformer saturation

Abstract

Owing to current transformer (CT) saturation caused by a decaying direct current component in the magnetizing inrush current, the restricted earth fault (REF) protection of a power transformer could maloperate during magnetizing inrush. This paper presents a new transformer restricted earth fault relay algorithm that can prevent false relay tripping and provide proper action during the energization of a faulty transformer. The integral of the product of the signals that are compared is calculated over 1 half-period of the signals. The performance of the proposed algorithm is tested and verified using a large number of transformer energization trials and fault cases. The signals required for testing of the algorithm were obtained by laboratory measurements, and then the algorithm was tested off-line. The influence of different levels of CT saturation due to different remanent fluxes in CT cores during power transformer energization was investigated. By applying computer simulations, the signals required for algorithm testing were generated. The investigation results presented in this paper show that the new algorithm provided sensitive protection for the power transformer for phase to ground faults and high security and stability during magnetizing inrush conditions in conjunction with CT saturation.

Presenting an Adaptive Restraint Method to Improve Performance of Ground Differential Protection of Power Transformer

“…To detect the inrush current in power transformer protection, the value of the second harmonic component of the currents is compared with a predetermined value [7]. On the other hand, in some conventional GD relays, the angle between residual and neutral currents is used to avoid malfunction during external ground faults (and some inrush current cases) [14,15]. But these methods do not guarantee malfunction prevention.…”

Transformer Faults Classification Based on Convolution Neural Network

“…The two-instantaneous-value-product algorithm has been used for recognizing fault and inrush currents by extracting the current amplitude variations [18]. Krstivojevic and Milenko presents an algorithm that prevents false tripping of the restricted earth fault relay during the transformer energization [19].…”

A New Simple Method to Avoid Maloperation of Transformer Restricted Earth Fault Relay during External Fault Events

“…However, if the neutral current is enough high during a potential case of maloperation, this method will not be helpful. The Krstivojevic and Djurić [15,16] proposed a new REF algorithm based on a time domain phase comparator that yields desirable results for inrush current condition and only single phase to ground type of external fault. Ebadi et al [17] have designed a new REF relay based on artificial intelligence which is slower than conventional method.…”