Short tail lightning impulse behaviour of medium voltage line insulation

Insulation failure in the medium voltage (10-20 kV) and electric traction lines (3 kV dc) is mainly due to indirect and direct lightning strokes to the lines. The overvoltages stressing the insulation have an impulse shape with a very short tail, much shorter than the standard 1.2/50 ps wave. The paper presents the results of experimental tests performed with a 1.2/4ps wave, on air gaps and insulators in use in the lines under consideration. The flashover probability distributions and the voltagetime to breakdown characteristicts under 1.2/4ps waves determined are presented and compared with the 1.2/50ps.