Virtual Zero Point (of an Impulse)    IEEE and IEC

Point on a graph of voltage versus time or current versus time determined by the intersection between the time axis at zero voltage or zero current and the straight line drawn through two reference points on the front of the impulse. Also referred to virtual origin of an impulse.

Note 1 For current impulses the reference points shall be 10 % and 90 % of the peak value.

Note 2 This definition applies only when scales of both ordinate and abscissa are linear.

Note 3 If oscillations are present on the front, the reference points at 10 % and 90 % should be taken on the mean curve drawn through the oscillations.