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About the reason for the burnout of the varistor

In the circuit, the role of the varistor is: first, overvoltage protection; second, lightning resistance requirements; third, safety testing requirements. Then why does the varistor burn out in the circuit? What is the reason?

Varistors generally play a role in voltage protection in circuits, and can be used with fuses for lightning strike or other overvoltage protection. It is usually used for lightning protection. When an overvoltage occurs, the varistor will be broken down and a short circuit will occur, so that the voltage at both ends of the varistor will be clamped at a lower position. At the same time, the overcurrent caused by the short circuit will burn the front fuse or Force the air switch to trip, thereby forcibly cutting off the power supply. Generally speaking, it has little effect on other electronic components after damage, just check the circuit components connected to it. In the case of puncture damage, the fuse will blow.

When the voltage is less than the rated voltage of the varistor, the resistance of the varistor is infinite and has no effect in the circuit. When the voltage in the circuit exceeds the varistor voltage, the resistance of the varistor will drop rapidly, which will play the role of shunt and voltage limiting, and the fuse in the same circuit will be blown to play a protective role. If there is no fuse in the circuit, the varistor will burst directly, be damaged and fail, lose its protective effect, and cause the subsequent circuit to burn out.
The above three reasons are the reasons that cause the varistor to burn out in the circuit. Special attention should be paid to the operation in the future to avoid damage to the capacitor.