How to Detect Faults of Clamp Ammeter for DC Earthing system
If there is a problem with the grounding of the DC busbar system in transformers, substations, and distribution rooms, testing or searching is a very troublesome task. Usually, staff use a multimeter for segmented search, which not only affects work efficiency but also makes the search inaccurate. It is necessary to measure the DC line section by section to remove some high-voltage equipment from protection, which seriously affects accuracy.
The method of online searching for DC bus fault grounding without affecting the operation of the DC system. The grounding selection of the substation DC system mainly adopts low-frequency signal injection method, DC leakage current detection method, and pull-through method. The injection method is susceptible to the influence of distributed capacitance; The pull-in 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 device cost constraints, sensor sensitivity cannot be guaranteed, and line selection sensitivity is limited.
None of the three methods can ensure 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 type leakage Ammeter is used to test the grounding of the positive or negative conductor of the DC system of the substation, its grounding leakage current is the largest; When the grounding resistance is high, the leakage current is small, which may be less than 1mA. Therefore, clamp type Ammeter for direct measurement of ground leakage current must meet the following requirements:
1. Capable of measuring the clamped wire cores (single or multi-core),
2. The test resolution should be very small (micro ampere clamp Ammeter),
3. High precision and small error
Clamp the positive and negative wires of the DC line together to measure DC leakage. Measure AC leakage by clamping the live and zero wires of the AC together. 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.
