High maintenance switch, mobile substation friends may have seen in the above elements, this is the Zinc Oxide high voltage varistor, will generally be in parallel with the main circuit, the overvoltage protection element. The utility model is mainly used for suppressing the over voltage, the resonance overvoltage and the lightning induced overvoltage of the electrical system. The above diagram is the application of the connection mode in the GBP9L-6G mining flameproof high voltage vacuum distribution equipment.

Protection principle:
According to the volt ampere characteristics of the varistor, the varistor can be divided into three working areas: the pre breakdown region, the breakdown region, and the rising region. In the region, the voltage applied to both ends of the varistor is less than the varistor voltage. Therefore, the equivalent of a varistor insulation 10M resistor above, then the resistance current of the varistor only microamp level can be seen as open. This region is the state of the varistor in the normal operation of the circuit.
Breakdown region: varistor voltage applied to both ends of the varistor voltage is greater than one, which belongs to the conductive tunnel breakdown electron conduction mechanism, the volt ampere characteristic is nonlinear conductivity excellent characteristics, in the breakdown region, a sharp change of small changes in varistor voltage can cause current, voltage sensitive resistor is used this feature to inhibition of voltage and surge energy absorption or release of overvoltage caused by.
Rise region: when the voltage is too large, so that the current through the varistor is greater than about 100A/cm2, the volt ampere characteristic of the varistor is mainly determined by the characteristic of the grain resistance. The I-V characteristics of varistor linear conductance, current and voltage rise almost linearly, varistors in the region has deteriorated, lost its energy characteristics such as over-voltage suppression, absorption or release of surge.
According to the conduction mechanism of varistor, the speed of its response to overvoltage quickly, so long as the selection and use of appropriate varistors on transient lines appear had excellent inhibition effect of voltage, so as to achieve the other element from overvoltage protection circuit damage to.