What tests are needed after replacing a current transformer?
Jun 12, 2026| I. Transformer Ratio and Polarity Test (Core Function Verification) Apply a test current using a transformer ratio and polarity tester to measure the secondary output.
Transformer Ratio: The measured value should match the nameplate value (e.g., 400/5), with an error not exceeding ±1%.
Polarity: The phase difference should be 0° (same polarity). If it is 180°, the polarity is incorrect and must be corrected immediately.
✅ Purpose: To ensure correct sampling in the metering and protection circuits, preventing the energy meter from reversing or the differential protection from malfunctioning.
II. Insulation Resistance Test (Safety Baseline Detection) Use a 2500V megohmmeter to measure the insulation of critical components:
Primary side to secondary side ≥ 1000MΩ
Primary side to ground ≥ 1000MΩ
Secondary side to ground ≥ 10MΩ
⚠️ If any item is below the standard, it indicates a risk of insulation breakdown, and operation is prohibited.
III. Load Operation Verification (Final On-Site Confirmation)
No-Load Power-On Test: Without connecting any load, power on and observe for 5 minutes. No abnormal noise, overheating, or smoke should be observed.
Data Verification After Connecting Load: Use a clamp meter to measure the primary current and compare it with the secondary instrument readings to verify the consistency of the transformation ratio.
Observe whether the energy meter is measuring in the correct direction and whether the power and power factor displays are normal.
Protection Circuit Interlock Test (If Applicable): Simulate a fault signal to verify whether the relay protection device can operate correctly.
