Virtual Duration of Wave Front    IEEE and IEC

(of an impulse) The virtual value for the duration of the wave front is as follows:

1. For voltage waves with wave front durations less than 30µs, either full or chopped on the front, crest, or tail, 1.67 times the time for the voltage to increase from 30% to 90% of its crest value.


2. For voltage waves with wave front durations of 30µs or more, the time taken by the voltage to increase from actual zero to maximum crest value.


3. For current waves, 1.25 times the time for the current to increase from 10% to 90% of crest value.