Researches on relay misoperation effected by the earth capacitance

Under some grounding states, the substation´s DC system works well, but the switching processes of the insulation resistance bridge in monitoring device might lead to a relay misoperation, that is, such an operation may generate a voltage fluctuation of the relay and when the maximum voltage value exceeds the protection value, the relay will misoperate. When state changes, the earth capacitance will charge or discharge, the influence caused by earth capacitance to the voltage fluctuation has been researched. The maximum value of voltage fluctuation is calculated using the Laplace transform. Then DC system has been simulated in RT-LAB, as the earth capacitance value in the system changes from small to large, the voltage changes as well, so the relationship curves of them are gotten to expose the influence on the maximum relay voltage fluctuation made by the earth capacitance. At the end, experiments are carried out to support the simulation results.