How to detect faults in DC grounding systems using clamp ammeters
If there is a problem with the grounding of the DC busbar system in transformers, substations, and distribution rooms, it is very troublesome to detect or search for it. Usually, staff use a multimeter for segmented searching, which not only affects work efficiency but also makes the search unsafe. It is necessary to measure the DC line section by section to disconnect some high-voltage equipment from protection, which seriously affects safety issues.
The method of online searching for DC bus fault grounding without affecting the operation of the DC system. The grounding selection of the DC system in the substation mainly adopts low-frequency signal injection method, DC leakage current detection method, and pulling method. The injection method is susceptible to the influence of distributed capacitance; The pull method cannot select the grounding branch with parasitic circuits; The DC leakage current detection method requires the installation of DC leakage current sensors in each branch. Due to cost constraints, the sensitivity of the sensors cannot be guaranteed, and the sensitivity of line selection is limited.
None of the three methods can guarantee correct line selection. Therefore, the DC leakage current detection method has been slightly improved, and the measurement of leakage current has been changed to a high-precision DC clamp ammeter. When testing the positive or negative wire grounding of the DC system in a substation using a DC clamp leakage current meter, the maximum grounding leakage current is observed; When the grounding resistance is high, the leakage current is small, possibly less than 1mA. Therefore, clamp type ammeters that directly measure ground leakage current must meet the following requirements:
1. Capable of measuring the clamped wire core (single core or multi-core),
2. The resolution for testing needs to be very small (microampere clamp ammeter),
3. High precision, small error
Clamp the positive and negative wires of the DC line together to measure the DC leakage. Clamp the live and neutral wires of the communication together to measure the AC leakage. Clamp the ground wire and measure the leakage current of the ground wire. Clamp the main line and measure the current of the main line.
