The protection principle, varistor varistor is a pressure limiting protection device, using the nonlinear characteristics of the pressure sensitive resistance, when overvoltage appears between the poles, varistor voltage clamp can be to a relatively fixed voltage value, so as to realize the level after circuit protection.
Varistor is also a very important role, is used for the transient overvoltage protection circuit.
Although it flow capacity is big, but are less energy capacity.
In addition, because it has the largest impact current pulse width is far less than the actual width of pulse current, large and medium-sized power semiconductor system so would often short-circuit or burn and failure phenomenon.
Second, varistor varistor damage reason analysis of failure mode is mainly short circuit, however, a short circuit will not cause damage of pressure-sensitive electrical resistance, for the resistance and is in the power supply to the entry of the positive and negative;
Insurance is a proof of that is not caused by short circuit or over current, it is possible that surge energy is too great, beyond the absorbed power burned varistor;
When by over current is too big, can also cause the valve burst open.
Then, according to a pressure sensitive resistance damage what are the reasons?
1, the number of over-voltage protection;
2, working temperature around;
3, varistor have squeezed;
4, whether through quality certification;
5, surge energy is too great, beyond the absorbed power;
6, the pressure is not enough;
7, and surge current is too large, and so on.
And short service life of varistor, after repeated impact performance will decline, thus composed of varistor lightning protection device problems of maintenance and replacement after using for a long time, this time we will pay attention to when choosing varistor;
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