Insulation monitoring and measuring point influence of substation DC system based on leakage current

Insulation monitoring of substation DC system is the key to detect cable defects in advance and ensure the reliable operation of protection and control system. At present, the conventional configuration of DC insulation monitoring system in substation is to use balanced bridge to monitor the inter-pole resistance in real time, use rotating switch unbalanced bridge to detect the positive/negative insulation resistance to the ground, and use leakage current to detect and locate the fault branch. However, the current calculation method of insulation resistance using voltage signal needs to monitor the voltage of positive and negative pole buses to the ground in real time, which requires a lot of equipment. Therefore, this paper studies the simulation modeling method of low-voltage DC system in substation considering the stray parameters of control cables, proposes the calculation method of insulation resistance based on leakage current, and analyzes the influence of the grounding position of the shielding layer on the installation position of leakage current sensor. In order to effectively measure the leakage current, the sensor can be directly stuck outside the control cable when the end of the shielding layer is grounded; When the first end of the shielding layer is grounded, the sensor should be clamped on the grounding shielding layer.