Measurement of Steep Impulse Residual Voltage on Surge Arrester Blocks

It's been decades since surge arresters became an integral part of power system. It protects the power system equipments by clamping the voltage to a safe level during the event of surge. The non linear characteristics of the metal oxide blocks used inside the arrester plays an important role in the operation of the arrester. The difference in the basic insulation level of the power system equipment and residual voltage of the arrester defines the protection margin of the system. The protection level of the arrester depends on the magnitude and steepness of the impulse current waveform, therefore the residual voltage across the arrester increases as time to crest reduces. Power system is subjected to fast transients caused due to bushing flashovers within valve hall, restrike of interrupting contacts, current chopping, etc. A higher residual voltage is observed when the arrester is subjected to a steep current surge, which in turn reduces the protection margin and in some cases even damaging the equipment. Steep impulse residual voltage consists of an inductive component that depends on the length of the arrester and a non-inductive component which is the property of the arrester block. This paper highlights the importance of estimating the non-inductive voltage drop across the arrester block as per relevant standards and computing protection level of the complete arrester when subjected to steep impulse current waveform in order to conduct proper insulation co-ordination study.