How to detect faults in the DC grounding system using a clamp-type ammeter
If there is a problem with the DC bus system grounding of transformers, substations, and distribution rooms, it is very troublesome to detect or find it. Usually, workers use multimeters to search in sections, which not only affects work efficiency but also makes the search inaccurate. It is necessary to measure the DC line section by section, so that some high-voltage equipment will be out of protection, seriously affecting safety issues.
Methods to find DC bus fault grounding online without affecting the operation of the DC system. The grounding line selection of the substation DC system mainly uses the low-frequency signal injection method, the DC leakage current detection method and the pull-through method. The injection method is susceptible to the influence of distributed capacitance; the pull method cannot select lines for ground branches with parasitic loops; the DC leakage current detection method requires the installation of DC leakage current sensors in each branch. Due to the cost constraints of the device, the sensor sensitivity cannot be guaranteed. , the line selection sensitivity is limited.
None of the three methods ensures 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 meter tests the positive or negative conductor of the substation DC system is grounded, the ground leakage current is the largest; when the ground resistance is large, the leakage current is small, possibly less than 1mA. Therefore, a clamp-type ammeter that directly measures ground leakage current must meet the following requirements: 1. Be able to measure the clamped wire core (single-core or multi-core), 2. The test resolution must 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 AC live and neutral wires 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.
