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Battery Sizing and Maintenance at a Small Electric Utility

Sepehr (Sep) Mogharei P.

Michael Winton

The increase in continuous loads such as radio transmitters and microprocessors in substations has led some utilities, including ours, to take a closer look at the sizing of the stationary batteries that operate those stations when commercial power is lost. Critical functions, such as tripping circuit breakers and conununicating information to dispatch centers, are placed on DC power. When station power is present, that DC power for the continuous loads is supplied by the charger. When conunercial power is lost, however, the continuous loads are carried by the batteries, which must also have the capacity to operate tripping mechanisms. IEEE Standard 485 I is widely accepted as the guideline for sizing of stationary batteries, and its application is discussed. Once a battery is placed in service, its maintenance, monitoring and periodic testing protocols are the next issues that the utility considers. Those practiced by this utility are discussed, including monitoring of the presence of DC power at certain critical points by SCADA equipment.

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