An experimental study on corona q-u curves under non-standard lightning impulses

•An experimental study is performed on the q-u (charge-voltage) curves under damped oscillation impulses.•The measurements show that the q-u curves under damped oscillation impulse are distinguished by oblate helix minor loops.•The characteristic parameters of the q-u curves are investigated systematically.•The energy dissipated in these minor loops exhibits an obvious polarity effect.

Considering that a majority of lightning surges intruding into substations present non-standard form, an experimental study is performed on the q-u (charge-voltage) curves under damped oscillation impulses in a corona cage. Based on the measured results, a comparison is made between the q-u curves under damped oscillation and double exponential impulses. The oscillation frequency and damping time constant are varied to investigate their effect on the characteristic parameters of the q-u curves. A preliminary discussion is also given for explanation of the formative mechanism of the oblate helix minor loops appearing on the q-u curves.