Pollution flashover of insulator strings is one of the most harmful natural disasters to transmission line

and further to power grid. The authors take suspension glass insulators as the test objects

and choose 0.5/5 μs

2.6/50 μs and other non-standard impulse voltage waveforms for test waveforms. Test results show that:1)the equivalent salt deposit density（ESDD） has more significant impact on flashover voltage than the non-soluble deposit density（NSDD）;2)for lower ESDD and NSDD

impulse voltage waveforms have little effect on flashover voltage; 3)for a fixed NSDD

flashover voltage decreases with the increase in ESDD

but for a fixed ESDD

flashover voltage shows a trend of first decreasing then increasing. When the ratio of NSDD to ESDD is fixed at 5/ 1

the flashover voltage corresponding to ±2.6/50 μs impulse voltage waveform shows an increasing trend with ESDD

but under ±0.5/5 μs impulse voltage waveform it shows a U-shaped curve trend evidently. The flashover voltage of insulator string decreases with the wave tail time increasing

and this trend is more clear with the increase in ESDD.