How to Use Overvoltage Protection Varistor Correctly

As a widely used varistor, overvoltage protected varistor is often used to protect thyristor rectifier. How should we choose a suitable over-voltage protection varistor? In general, the 3kA varistor model is usually used for surge absorption of electrical equipment, while the 5kA resistor model is mostly used for the protection of lightning strikes and overvoltage absorption of electronic equipment. Here we take lightning protection as an example.

Usually in the test, we choose the common synthetic wave (the voltage wave of 1.2 / 50 μ s when the generator output is open circuit; the current wave of 8 / 20 μ s when the short circuit output; the internal resistance of the generator is 2 Ω) to check the ability of the equipment to resist the lightning surge interference on-line. In the 4kV test, the current absorbed by the over-voltage protected varistor is up to 2 kA. For the 6kV test, the absorption current value is 3kA. However, in the actual selection, we should also appropriately increase the current capacity of the selected over-voltage protection varistor.