ZnO surge arrester elements with mixed direct and 50 Hz voltages

The characterisation of surge arrester elements allows equivalent circuit representations to be developed. HV tests with variable-frequency supplies have been extended to mixed DC and AC measurements. This is not only relevant to HVDC systems but also to the effect of preconditioning. A new test arrangement allows accurate measurement of such mixed voltage and evaluation of RMS and peak currents and voltages and mean power. An equivalent circuit has been developed which adequately incorporates the mixed-voltage behaviour. A progressive transition of characteristics is found as K(V_ac/(V_ac+ V_dc)) is varied from zero to unity. A minimum is found for certain K and voltage values in the power consumption in the arrester element.