Doble Engineering Company

Surge arresters are often “overlooked ” when performing Power Factor tests on transformers, breakers and other apparatus in a substation. Often times, the testers are aware of how a transformer or a breaker functions, but are not aware of the intended purpose of the surge arresters. Since there are no “moving ” parts to maintain or an oil sample to pull, it is often their policy not to perform any testing of the arrester. Surge arresters are devices that help prevent damage to apparatus due to high voltages. The arrester provides a low-impedance path to ground for the current from a lightning strike or transient voltage and then restores to a normal operating conditions. A surge arrester may be compared to a relief valve on a boiler or hot water heater. It will release high pressure until a normal operating condition is reached. When the pressure is returned to normal, the safety valve is ready for the next operation. When a high voltage (greater than the normal line voltage) exists on the line, the arrester immediately furnishes a path to ground and thus limits and drains off the excess voltage. The arrester must provide this relief and then prevent any further flow of current to ground. The arrester has two functions, it must provide a point in the circuit at which an over-voltage pulse can pass to ground and second, to prevent any follow-up current from flowing to ground