How to inspect a current transformer after installation?
Nov 26, 2025| Inspection steps after current transformer installation:
1. Visual inspection: Confirm that the ceramic parts are free of cracks, damage, or discharge marks, and that the casing is free of oil leakage (oil-immersed type) or carbonization (dry type).
Check that the nameplate information is clear, the wiring terminals are secure, and the grounding wire connection is reliable.
2. Insulation performance test: Use a 1000V megohmmeter to measure the insulation resistance between the primary coil and the secondary coil, and between the primary/secondary coil and the casing. The resistance should be ≥50MΩ.
3. Polarity verification: Use a DC milliammeter method: the needle should swing forward when the battery is connected and backward when disconnected to confirm correct polarity.
4. Turns ratio error test: Apply primary current and measure the secondary current to calculate the turns ratio error (e.g., the error of a 50/5 current transformer must conform to the manufacturer's specifications).
5. Secondary circuit inspection: Ensure that the secondary side is not open-circuited, that instruments are properly connected, and that the terminal blocks show no signs of arcing or burning. 6. Operational Status Monitoring
Listen to the sound: A uniform "humming" sound is normal; abnormal sounds may indicate a loose core or a secondary open circuit.
Check that the connections are not overheating, the oil level (for oil-immersed systems) is normal, and there is no burnt smell.
Precautions: Open circuits on the secondary side are strictly prohibited, as this may cause a high-voltage hazard.
Special checks are required after lightning strikes or heavy rain.
