Performances of high-voltage glass insulators subjected to fast transient overvoltages

Steep-front, short-duration voltage pulses occur in power systems as a consequence of lightning, switching of the increasingly used gas-insulated switchgears or by electromagnetic pulses of very high amplitude. Such overvoltages characterised by very fast rise time may produce irreversible damages to the insulation of the different apparatuses of an electric power line. Test results will be presented in this paper concerning the behaviour of cap and pin-glass insulators subjected to steep-front overvoltages. In particular the effect of the glass composition on the insulator performance will be analysed for both normal and anti-fog configurations. Moreover; the dependence of the test results on the polarity of the applied voltage and the electrodes arrangement will also be discussed.