Influence of auxiliary dc system capacitance on relay protection operation

Auxiliary DC systems that have considerable capacitance to ground, and that have balanced voltages between the DC polarities and ground, are at risk for false operation of switched DC loads. This can happen if an unintended ground develops at the critical points in the DC system. The sources of these large capacitances were investigated, as well as the vulnerability of sensitive interposing relay to false operation due to the unintended ground. An Electromagnetic Transient Program (EMTP/ATP) based simulation was performed to check the influence of the DC system and interposing relay parameters on the possibility of false operation. Means to eliminate the false operation are discussed.