Minimizing capacitor bank outage time through fault location

Capacitor banks are critical substation assets that play a vital role in providing reactive power support, thereby increasing the power system capacity. High-voltage capacitor banks are constructed as single-wye, double-wye, or H-bridge configurations and can be grounded or ungrounded. Capacitor banks consist of a number of single-phase capacitor units connected in series and parallel to achieve the desired voltage and VAR rating. The capacitor units can be externally or internally fused, fuseless, or unfused. When the unbalance resulting from unit or element failures becomes too high, the capacitor bank needs to be taken out of service by the protection system before the resulting unit overvoltages lead to a cascading failure and the faulty units must be replaced. If the bank is externally fused, then the unit with the blown fuse is usually the faulty unit, making identification obvious. If the bank is internally fused, fuseless, or unfused, then fault location is difficult because usually there is no visual indication of the problem. The result of a prolonged inspection is an extended outage of the capacitor bank. Although it might not be possible to identify the faulty unit in an internally fused, fuseless, or unfused bank, identifying the faulted phase and section narrows the search area and helps minimize the outage time. This paper analyzes various capacitor bank configurations and proposes an economical method to help locate the faulty elements or units for each configuration. The paper also provides results that verify the proposed methods using a Real Time Digital Simulator (RTDS®).