The chopped-impulse test is often specified to represent the severe condition of stress within the apparatus (particularly in winding structures) produced by collapse of the voltage when a line or bus insulator flashes over near the apparatus. This test is a lightning-impulse test with the tail of the impulse chopped after the crest at some specified time. If the chopping occurs before the crest of the impulse, the test is known as a front-of-wave test.
