Different applications, the purpose of the application of varistor, the voltage/current acting on the varistor should not be the same, so the requirements of the varistor are not the same, pay attention to distinguish this difference, for the correct use is very important.
Depending on the purpose of use, varistors can be divided into two categories: ① protection varistors, ② circuit function varistors.
Protect the resistance
(1) To distinguish the varistors used for power protection, or the varistors used for signal and data line protection, they should meet the requirements of different technical standards.
(2) Varistors used across power lines can be divided into AC or DC types according to the different continuous operating voltages applied to the varistors. The aging characteristics of varistors under these two voltage stresses are different.
(3) According to the different characteristics of abnormal overvoltage of the varistor, the varistor can be divided into three types: surge suppression type, high power type and high energy type.
★ Surge suppression type: refers to the voltage sensitive resistor used to suppress lightning overvoltage and operating overvoltage and other transient overvoltage, the emergence of this transient overvoltage is random, non-periodic, the peak current voltage may be very large. The vast majority of varistors fall into this category.
U type high power: refers to the continuous bursts used for an absorption cycle of pressure-sensitive resistors, for example, and the varistor on switch power converter, the impulse voltage cycles, and the cycle, energy generally can be calculated, the peak voltage is not big, but because of the high frequency, the average power is considerable.
★ High energy type: refers to the voltage sensitive voltage device used to absorb the magnetic energy in the generator excitation coil, lifting electromagnet coil and other large inductance coils. For this kind of application, the main technical index is the energy absorption capacity. The protection function of varistors can be repeated many times in most applications, but they are sometimes used as "one-shot" protection devices such as current fuses. For example, short-circuit contact varistors connected to the load of some current transformers.
