Novel Method for Location of Internal Faults in Ungrounded Double Wye Shunt Capacitor Banks

Double wye shunt capacitor banks (SCB) are commonly used for reactive power support in high voltage transmission systems. Neutral current unbalance method is often used for protecting double wye SCBs against internal faults. One of the limitations of existing neutral current based unbalance methods is that they fail to detect simultaneous faults (same fault starting time or faults happening between two consecutive protection passes). This paper proposes a novel method for internal fault location in ungrounded double wye fused/fuseless SCBs. The proposed method uses compensated negative sequence and neutral currents to locate the internal faults. The advantage of the proposed method is that it can locate simultaneous faults happening in any of the two legs of SCB. The proposed method can also calculate the number of faulty elements. The performance of the proposed algorithm has been validated using both hardware experiments and software simulations. A laboratory scale prototype of ungrounded double wye SCB has been developed to test the performance of the proposed method. Software simulations have been done using PSCAD software. Results show that the proposed algorithm can locate both single and simultaneous faults even during system voltage unbalances. The proposed algorithm performs satisfactorily during load switching scenarios.