Pull a Few Strings: Complete Protection of Multistring Fuseless Capacitor Banks

THE TREND TOWARDS LARGE, fuseless shunt capacitor banks being employed in power systems is due to their lower cost, compact design, higher reliability with less exposed live parts, and lower losses. This article describes a novel application of the impedance method to provide complete bank protection by measuring the impedance of each series string of the capacitor bank. The scheme can identify the string(s) with an alarm or trip condition, keep the bank in service with pack failures in multiple strings, and trip only when the bank is actually in an unacceptable operating condition. Because this scheme can account for the distributed failure of packs in strings, bank availability can be increased.