How to Detect Faults with Clamp Ammeter in DC Grounding System
If there is a problem with the grounding of the DC bus system of the transformer, substation, and power distribution room, it is very troublesome to detect or find it. Usually the staff use the multimeter to search in sections, which not only affects the work efficiency but also is not safe to search. It is necessary to measure the DC line section by section, so that some high-voltage equipment will be out of protection, which will seriously affect the safety problem.
Without affecting the operation of the DC system, find the method of fault grounding of the DC bus online. The grounding line selection of substation DC system mainly adopts low-frequency signal injection method, DC leakage current detection method and circuit pulling method. The injection method is easily affected by distributed capacitance; the pull method cannot select the grounding branch with parasitic loops; the DC leakage current detection method needs to install a DC leakage current sensor in each branch, and the sensitivity of the sensor cannot be guaranteed due to the cost of the device. , the line selection sensitivity is limited.
None of the three methods can ensure the correct line selection. Therefore, the DC leakage current detection method is slightly improved, and the leakage current measurement is changed to a high-precision DC clamp ammeter. When the DC clamp leakage current meter tests the positive or negative wire of the DC system of the substation to ground, the ground leakage current is the largest; when the ground resistance is large, the leakage current is small, which may be less than 1mA. Therefore, the clamp ammeter that directly measures the earth leakage current must meet:
1. It can measure the clamped wire core (single core or multi-core),
2. The test resolution should be very small (microampere clamp ammeter),
3. High precision and 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 AC together to measure the AC leakage. Clamp the ground wire to measure the leakage current of the ground wire. Clamp the main line and measure the current of the main line.
