Inclusion of surge diverters in system overvoltage calculations

In transmission systems operating at the higher voltage levels, increasing use is being made of surge diverters as the first line of defence against overvoltages. The determination of the interaction between the surge diverters and the system is therefore becoming of prime importance. When studies of this interaction are to be performed numerically, means have to be developed for representing the surge diverter in the system-network equations. The present paper will describe a technique whereby the surge diverter can be included in transient overvoltage calculations based upon the modified Fourier-transform method. In this technique it will be demonstrated how system elements with voltage-dependent characteristics can be considered together with system elements with frequency-dependent characteristics. The use of the technique derived will be illustrated by studies on a simple transmission system in which surge diverters operate under switching-surge conditions.