BATTERY PROTECTION - WHERE DO WE STAND

Growing emphasis on operating reliability is leading both utility and industrial/commercial power system operators to confront a long-neglected system protection issue: proper fault protection for large batteries. Full-load current from a large UPS battery may reach thousands of amperes, with fault currents 10-12 times as high. Battery destruction during a major fault can acid-contaminate an entire building, escalating damage far beyond battery cost or equipment downtime alone. Existing IEEE standards, the NEC, other published standards, and supplier literature offer little help in applying fuses (seldom marketed with specific dc current or voltage ratings) or circuit breakers to battery circuits. Often, no protective devices at all are provided because of a fear of their nuisance operation. Of special concern is the "internal" fault that may go undetected by devices at a battery's main terminals. This paper will outline some user experience, bring together existing recommendations, and perhaps stimulate development of useful standard practices.