Researches on DC system relay misoperation with RT-LAB

When the substation DC system grounded though a high resistance, the inrush current is too small to be detected and this status will be kept without operation. But it brings a hidden danger to the substation, when the resistance bridges in the insulation monitoring device open and close, the voltage fluctuation of relay coil affected by the system parameters may lead to relay misoperation and power interruption. The authors researched the relationships between the relay misoperation phenomenon and various system parameters with RT-LAB software. They built a model of DC system with positive pole high resistance grounding, as well as physics experiments were carried out to verifiy the accuracy of simulation. By changing the system parameters from zero to infinite, characteristics curves of system parameter and relay voltage were obtained, the conclusion is given to report the contribution to the relay misoperation caused by increasing system parameter values, and it is useful for avoiding relay misoperation by adjusting system parameter values in a proper way.