The voltage/current stresses acting on varistors are not the same for the purpose of applying varistors in different applications, and thus the requirements for varistors are different. It is important to pay attention to distinguish such differences for proper use. Depending on the purpose of use, varistors can be distinguished into two main categories: varistors for protection and varistors for circuit function.
Protection varistors
1.Distinguish between varistors for power protection, or signal line, and data line protection, which have to meet the requirements of different technical standards.
2、According to the different continuous operating voltages applied to the varistor, the varistor used across the power line can be distinguished into two types for AC or DC, and the aging characteristics of the varistor under the stress of these two voltages perform differently.
3, according to the varistor withstand the abnormal overvoltage characteristics of the different varistor can be distinguished into surge suppression type, high power type and high energy type of these three types.
Surge suppression type: is used to suppress transient overvoltage such as lightning overvoltage and operating overvoltage varistors, the appearance of this transient overvoltage is random, non-periodic, the peak of the current voltage may be large. The vast majority of varistors fall into this category.
High power type: refers to the varistor used to absorb the continuous pulse group that appears periodically, such as the varistor connected in parallel to the switching power converter, where the shock voltage appears periodically, and the period is known, the energy value can generally be calculated, the peak voltage is not large, but the average power is quite large because of the high frequency of appearance.
High energy type: refers to the pressure-sensitive voltage device used to absorb magnetic energy in large inductive coils such as generator excitation coils, lifting solenoid coils, etc. For this type of application, the main technical indicator is the energy absorption capacity.
The protection function of the varistor, the vast majority of applications, can be repeated many times the role, but sometimes it is also made into a current fuse as a one-time protection device. For example, a varistor with short-circuit contacts connected in parallel to some current transformer loads.