Lightning impulse voltage and overshoot evaluation proposed in drafts of IEC 60060-1 and future UHV testing

Lightning impulse (LI) voltage testing is an indispensable method for quality assurance of high voltage (HV) and ultra high voltage (UHV) insulation. Not avoidable parasite inductances of the testing circuit provide an oscillation, known as overshoot, at the peak of the lightning impulse (LI). The present paper gives an overview of existing and proposed overshoot evaluation methods of LI voltage. An analytic derivation clarifies the relation between an overshoot magnitude- and overshoot magnitude-/duration- considering method. Hence the finding is derived that both methods provide similar results by applying power transformer testing. Moreover the current paper identifies that a higher permitted overshoot is required for UHV testing by keeping the front time of T₁=1.2 μs.