Time-Domain Protection and Fault Location of Wye-Connected Shunt Capacitor Banks Using Superimposed Current and Differential Voltage

This paper presents protection and fault location of wye-connected shunt capacitor banks used in medium or high voltage applications. The proposed method is sensitive to single element failure obtained by using voltage adaptive instantaneous superimposed current in each phase. The change in equivalent reactance computed using time-domain signals is used to find the number of failed capacitor element and types of fault. The location of the faulted capacitor is identified using sign of the voltage difference of the lower and upper halves of the shunt capacitor bank. The performance of the proposed method is tested for various cases including identical faults, simultaneous faults, system voltage unbalance in both single and double wye-connected shunt capacitor banks. The method is also validated using field data collected from a 400 kV SCB for an internal fault. The proposed technique is compared with available methods and found accurate.

I. Introduction

Shunt capacitor banks (SCBs) are used in electric power systems as an economical solution for reactive power support, power factor improvement and enhancement of steady state power transmission capacity [1], [2]. The SCB resides a large number of capacitor elements, typically in the range of several hundreds to a couple of thousands. The capacitor elements are connected in series and parallel to form a bank, and the number of elements in series and parallel depends on the voltage and reactive power rating of the bank. Failure of a capacitor element causes voltage stress and overcurrent in remaining elements in the SCB [3]. Such an event may lead to damage the dielectric material of healthy elements that may further cause the hazard of explosion or fire. Therefore, a sensitive protection of SCB is required that provides reliable and efficient operation. Further, the idea of location and number of faulted capacitor elements help in expedition of maintenance process and fast service restoration of the SCB.