On-line insulation monitoring of substation DC power supply

The disadvantages of present insulation monitoring of substation DC power supply system are pointed out and an online insulation monitoring method based on intelligent sensor and zero-crossing filter is proposed for DC power supply. The fault leakage current is detected by the intelligent sensors installed on every power supply circuits, and then sent to the monitoring computer via communication networks, which are processed by zero-crossing filter to eliminate the interference components. The grounding circuit and point are then effectively determined. The DC insulation variation of each branch is also monitored in real time and its downward trend is forecasted based on the historical data. The alarm criteria of instantaneous current limit violation and current change rate violation are put forward. The zero-crossing filter is also simulated. The validity of the proposed method is proved by on-site test.