AC Line Surge Protectors
Type 1 surge protection devices are combined lightning current and surge arresters that are used in unmetered areas. They are meant to protect against the effects of direct lightning strikes and must satisfy very stringent requirements. In order to meet these requirements, spark gap technology is required. A spark gap will break down during an abnormal voltage surge, safely shunting the surge to ground.
Type 2 surge protection devices with a low discharge capacity are installed in the metered area. They are generally installed in machine control cabinets or sub-distributions. They do not have to handle direct lightning strikes, but they must be able to discharge over-voltages from indirect lightning strikes or switching operations. Varistor technology is proven itself here. At low voltage, the varistor has a high electrical resistance which decreases as the voltage increases. When an over-voltage occurs, the varistor’s resistance drops, allowing the extra current to flow through the varistor and safely to ground.
Type 3 surge protection devices with the lowest discharge capacity are installed as close as possible to the end device. The devices have a wide range of designs to suit the various different installation environments. Type 3 surge protection is similar to type two, which is based on varistors, but the requirements concerning discharge capacity are lower compared to type 2.
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