Classification Of Surge Protectors By Purpose

Power Line SPD

Because the energy of a lightning strike is extremely large, a tiered discharge method is required to gradually dissipate the lightning energy to the ground. In the non-direct lightning protection zone (LPZ0A) or at the junction of the direct lightning protection zone (LPZ0B) and the first protection zone (LPZ1), a surge protective device or surge protector voltage-limiting device that has passed Class I classification testing is installed as the first-level protection device to dissipate the direct lightning current or, when the power transmission line is struck by direct lightning, the significant energy conducted. At the junction of subzones following the first protection zone (including LPZ1), a surge protection device voltage-limiting device is installed as the second, third, or higher-level protection device. The second-level protector is designed to protect against residual voltage from the preceding protector and induced lightning strikes within the zone. Even when the preceding protector absorbs significant lightning energy, some energy, which is significant for the equipment or the third-level protector, is still transmitted and needs to be further absorbed by the second-level protector. Furthermore, the transmission lines passing through the first-level arrester will also be susceptible to lightning electromagnetic pulse radiation. When the line is long enough, the energy of the induced lightning becomes large enough that a second-level protector is needed to further dissipate the lightning energy. The third-level protector protects against any residual lightning energy that passes through the second-level protector. Depending on the voltage rating of the protected equipment, if two levels of lightning protection can limit the voltage to below the equipment's withstand voltage, only two levels of protection are required. If the equipment's withstand voltage is lower, four or even more levels of protection may be required.