Low-Voltage Protective Equipment

Low Voltage Lightning Arresters Picture Low voltage lightning arresters are often mounted on the substation transformer just like the high voltage type to protect the transformer on the low voltage side.

The next piece of low voltage protective equipment is typically a circuit breaker. Circuit breakers protect the substation transformer as well as the distribution line or feeder connected to it from overloads and faults that occur out on the distribution line.

Circuit Breaker PictureIt will be set to trip or open at some level above the maximum normal current of the transformer, perhaps 200 to 250 percent of full load current. On very high currents, it will trip very quickly.

Most circuit breakers are set to re-close automatically. The basic reason is to maintain continuity of service to the greatest possible extent, without damaging equipment or creating an unsafe condition. Automatic reclosing devices interrupt the power in the event of a fault or short circuit, and then re-instate, or "reclose" the power after a fixed interval of time. Hopefully the fault will have "cleared" or fixed itself during that interval. If not, the breaker will re-open and lock in an open position until utility personnel arrive to determine the cause of the problem and correct it.