Selection of varistor flow capacity

The main parameters of varistor are nominal voltage, voltage ratio, control voltage, residual voltage ratio, current capacity, leakage current, voltage temperature coefficient, current temperature coefficient, voltage nonlinear coefficient, insulation resistance, static capacitance and so on.

Generally, the current-carrying capacity given by the product is the current that can be withstood when the varistor voltage change rate is less than ±10% of the initial value in the case of pulse test according to the waveform, impact number and interval time specified by the product standard. value. The number of impacts that a varistor can withstand is a function of waveform, amplitude, and interval time. When the amplitude of the current waveform is reduced by 50%, the number of impacts can be doubled. Therefore, in practical applications, the surge current absorbed by the varistor should be less than the flow capacity of the product, so that the varistor has a long working life.

When selecting the flow capacity, the main consideration is whether the varistor is used for lightning protection or to prevent operating overvoltages inside electronic equipment and equipment. Generally, the peak value of the induced lightning strike voltage is about 3.5 times the operating voltage. If it is mainly used for lightning protection, lightning protection varistor can be selected, and their flow capacity is 3kA, 5kA, 2OkA and other varieties. The actual detected lightning current is in the range of 200-3000A, and most of them are less than 1OkA. The inrush current generated by the internal operation of electronic instruments and equipment is generally less than 500A, and a general-purpose varistor can be selected.