Use of varistor

The varistor is generally used in parallel in the circuit. When the voltage across the resistor changes abruptly, the short circuit of the resistor blows the current fuse to protect it. Varistors are used in circuits and are often used for power supply overvoltage protection and regulation.

The reliability and safety of the power supply lightning arrester depend to a large extent on the correct use of the varistor. The following principles are available for reference. In particular, in the lightning protection design of the power supply, the differences in power quality, the frequency of lightning strikes and strength, the installation and use of the protected equipment, and the impact tolerance are also considered. Photocopy the set. Designed lightning protection devices must be tested and verified under field conditions or as close as possible to the actual conditions of the simulation.

1 calculation of varistor voltage:

Generally, it can be calculated by the following formula:

U1mA=KUac type: K is the coefficient related to power quality, generally K=(2~3), cities with better power quality may be smaller, and rural areas (especially mountainous areas) with poor power quality may be larger. Uac is the rms voltage of the AC power supply. For 220V ~ 240V AC power supply lightning arrester, varistor with varistor voltage of 470V ~ 620V should be selected. Selecting a varistor with a higher varistor voltage can reduce the failure rate and prolong the service life, but the residual voltage is slightly increased.

2 Calculation of nominal discharge current:

The nominal discharge current of the varistor should be greater than the surge current required to withstand or the maximum surge current that may occur each year. The nominal discharge current should be calculated from the value of the shock resistance life cycle number in the calibration curve for more than 10 times, which is about 30% of the maximum impact flow rate (ie 0.3 IP).

3 parallel connection of varistor:

When a varistor does not meet the requirements of the nominal discharge current, multiple varistor should be used in parallel. Sometimes in order to lower the limiting voltage, multiple varistors are used in parallel even if the nominal discharge current meets the requirements. It is important to note that when the varistor is used in parallel, it is necessary to strictly select the parameters with the same parameters (for example: ΔU1mA≤3V, Δα≤3) for pairing to ensure uniform distribution of current.