Transient inrush current detection and classification in 230 kV shunt capacitor bank switching under various transient‐mitigation methods based on discrete wavelet transform

Abstract

To avoid the failure of instantaneous overcurrent relays (50) owing to fails triggered by transient inrush currents during capacitor-bank switching, this study describes a new approach to detect and classify high-transient inrush current. These currents are due to the energisation of a shunt capacitor bank, rated 4 × 72 Mvar/230 kV, in a substation system in Thailand. The simulation tool power systems computer-aided design (PSCAD) is used to simulate the transient inrush current using six transient-mitigation methods, i.e. (i) a base case, (ii) a pre-insertion resistor, (iii) a pre-insertion inductor, (iv) a current-limiting reactor, (v) a series 6% reactor and (vi) synchronous closing control. Inrush current signals from PSCAD were used as inputs for discrete wavelet transforms. On a scale from 1 to 30, the maximum value of the wavelet coefficient is used to detect the inrush current. The high value of the standard deviation of the wavelet-scale analysis is used to discriminate between the high transient inrush current and the normal capacitor rate current. The results obtained show that the newly proposed method effectively detects and discriminates the capacitor switching inrush current, both isolated and back-to-back switching, with high accuracy.