How to troubleshoot after the secondary side grounding fault of the current transformer?

1. Appearance inspection
Grounding wire inspection: First, perform an appearance inspection on the grounding wire connected to the grounding terminal of the secondary side of the current transformer. Check whether the grounding wire has obvious fractures, damage or burnt marks. For example, check whether the insulation sheath of the wire is cut or worn, which may expose the metal core inside the grounding wire, thereby affecting the grounding effect. At the same time, check whether the connection between the wire and the grounding terminal is loose, and whether the connecting nut shows signs of falling off.
Grounding terminal inspection: Check whether the grounding terminal has corrosion or oxidation. In some harsh environments, such as humid or chemically corrosive gas environments, the grounding terminal may be corroded, resulting in increased grounding resistance. Also check the fixing of the grounding terminal to ensure that it is firmly installed on the equipment or grounding bus.
2. Grounding resistance measurement
Use a grounding resistance tester: Use a professional grounding resistance tester to measure the grounding resistance of the secondary side of the current transformer. Connect the test wire of the tester to the grounding system in the correct way, usually connect one test wire to the grounding terminal and insert the other test wire into the soil at a certain distance (such as 20 meters, 40 meters) from the grounding electrode. Measure according to the operating instructions of the tester. Under normal circumstances, the grounding resistance should be less than 10 ohms.
Compare historical data and standard values: Compare the measured grounding resistance value with the historical data. If the resistance value increases significantly and exceeds the normal range, it means that there may be a fault in the grounding system. At the same time, refer to the relevant electrical equipment standards to determine the qualified range of grounding resistance. For example, for the secondary grounding of the current transformer with high precision requirements, the grounding resistance may be required to be lower.
3. Insulation resistance detection
Application of insulation resistance meter: Use an insulation resistance meter (megohmmeter) to check the insulation resistance between the secondary winding of the current transformer and the ground. Connect the two test terminals of the insulation resistance meter to the secondary winding and the ground terminal respectively, shake the handle of the insulation resistance meter at an appropriate speed (such as 120 rpm) to read the insulation resistance value. Generally speaking, the insulation resistance between the secondary winding and the ground should meet the specified requirements of the equipment, and the insulation resistance is usually required to be above several megohms.
Determine insulation fault: If the insulation resistance value is too low, it may indicate that there is a problem with the insulation between the secondary winding and the ground. This may be caused by aging, moisture or mechanical damage to the insulation of the winding. For example, in a long-term humid environment, the insulation material of the winding may absorb moisture, resulting in a decrease in insulation performance.
4. Loop check
Check the connected equipment and loops: Check the equipment and loops related to the secondary grounding of the current transformer, including the grounding of the connected relays, ammeters and other equipment. Check whether the grounding of these devices is good and whether there is a ground short circuit or open circuit. For example, if the internal grounding of the connected relay is poor, it may affect the performance of the entire secondary grounding system.
Troubleshoot interference sources and abnormal current paths: Look for possible interference sources and abnormal current paths. Check whether there is electromagnetic interference generated by large electrical equipment around, which may affect the normal operation of the grounding system. At the same time, check whether there are other unexpected conductive paths, such as accidental contact between the metal casing and the grounding system, which may cause grounding faults.