# How to Select the Waveform for Impulse Withstand Voltage Test

HIMALAYAL - SHANGHAI - CHINA

In the early days, the impulse withstand voltage test can be used to detect electrical equipment’s insulation performance when they are subject to atmospheric overvoltage or lightning. Later on, the test is applied to study the insulation performance when the electrical equipment is subject to switching overvoltage.

The impulse withstand voltage tests can be divided into two categories according to insulation property of test objects. The first category is the withstand voltage test, which is performed on non-self-restoring insulation or combination test objects. The second category is the destructive discharge test, which is conducted on self-restoring insulation test objects. The impulse voltage generator is a kind of HV generating device and can be applied for impulse withstand voltage tests. In the withstand performance tests, the impulse voltage can generate standard full wave (lightning wave), chopped wave, switching wave and steep wave, which can meet the requirements of impulse withstand voltage tests for all kinds of electric equipment.

Full wave: full wave is a kind of non-periodic impulse voltage waveform with certain polarity; the voltage of front wave rises quickly and goes down slowly to zero after reaching the peak value.

Chopped wave: after a certain time delay of lightning impulse voltage full wave,  the waveform which is chopped by external gap is named chopped wave. According to the length of chopped time delay, the chopped wave can be divided into wave front chopping and wave tail chopping.

Switching wave: the principle of defining front time Tcr and tail time T2 is  same as lightning wave. The impulse wave, which meets the requirements - Tcr =250μs and T2=2500μs, is called standard switching wave.

Steep wave: the voltage converts from high to low but its performance does not change. This kind of wave is called steep wave.

The causes of forming these four waveforms are different. When the impulse withstand voltage test is performed on electrical equipment, the impulse  generator should also be equipped with different waveforms based on different test objects.