Accelerated ageing tests on composite hollow insulators under DC voltages

Investigations are reported on two specimen of silicone rubber hollow insulators at a DC voltage of - 1oo kV. Leakage current measurements are performed under natural pollution conditions and with artificial wetting. On the surface ofnaturally polluted insulators energised with DC voltage several types ofsimple microbes were found, which may influence the leakage current performance. It is also shown that accelerated ageing procedures using salt fog for creating surface discharges are not representative for inland sites with a low degree of pollution. Ageing performance of non-ceramic insulators should be checked in general with respect to the UV-strength of the material used. Accelerated ageing tests regarding pollution performance are necessary only if the site conditions will create surface discharges on the non-ceramic material chosen for the insulator. A test procedure, based on the IEC 1 000 h test, with constant discharge activity over a selected duration is proposed for further investigation. There is no advantage regarding creepage distance dimensioning ofnon-ceramic insulators in comparison to porcelain insulators for sites with surface discharges under natural conditions. The use of non-ceramic insulators for areas with very heavy or extreme pollution seems to be questionable.