Effect of energy and voltage ratings of ZnO protective systems of series capacitors on transient stability and transient torques

The effect of voltage and energy ratings of ZnO protective systems of series capacitors on the transient stability and the transient torque phenomenon of a power system is investigated. Bonneville Power Administration´s Electromagnetic Transients Program (EMTP) is used for the studies. The stability studies are also carried out by a stability program and the results are compared with the EMTP results. The investigations show that the system switching strategy, the frequency of the inertial mode, and the systems susceptibility to SSR (subsynchronous resonance), are also important factors in proper determination of voltage and energy ratings of ZnO protective systems. As compared with the EMTP results, the stability program results are erroneous if the effect of ZnO protective systems of series capacitors is not considered in the analysis. Incision of capacitor-varistor linear models in a stability program results in optimistic stability margins. However, the results can be accepted with a fair degree of confidence