Impact of time to flashover of gapped silicon carbide arrester on insulation co ordination of substation. A model study

Presently gapped silicon carbide arresters are rarely purchased for the protection of substation equipment and they are gradually replaced by metal oxide arresters. But gapped arresters form the bulk of the protection equipment and have been in use for more than 10 years. These arresters have undergone extensive deterioration and often are reported to have failed. The deterioration of their components, such as the electrodes forming the gaps, causes a significant change in their breakdown characteristics. A TNA model has been used to study the effect of change in the breakdown time on the voltage rise at the transformer end of a 132 kV substation under impulse voltage. A rise of 35% in the potential over the BIL at the transformer end is noticed when an impulse strikes the incoming line of a substation and when the breakdown time of the spark gap changes from 0.6 /spl mu/S to 4.0 /spl mu/S. The model simulation has been supported by computer simulation in Pspice.