Transformer Acceptance Tests (Pre-Commissioning Checks)

Before a transformer is energized and put into service, it must undergo acceptance testing to ensure it meets design specifications, manufacturer guarantees, and industry standards. These tests verify performance, safety, and reliability.

1. Routine Tests (IEC 60076 / IEEE C57.12.00)

Performed on all transformers before delivery:

a) Insulation Resistance Test (Megger Test)

• Measures insulation quality (winding-to-winding & winding-to-ground).

• Test Instrument: Megohmmeter (5kV or 10kV for HV transformers).

• Acceptance Criteria: Minimum 1 MΩ per kV (e.g., 33 MΩ for 33kV).

b) Winding Resistance Test (DC Resistance)

• Checks for loose connections, broken strands, or tap changer issues.

• Test Method: DC current injection (Kelvin bridge or micro-ohmmeter).

• Acceptance Criteria: Compare with factory data (deviation < ±2%).

c) Turns Ratio Test (TTR Test)

• Verifies correct voltage transformation ratio.

• Test Instrument: TTR (Turns Ratio Test) meter.

• Acceptance Criteria: ±0.5% of nameplate ratio.

d) Polarity & Vector Group Test

• Ensures correct phase relationship (Dyn11, YNd1, etc.).

• Test Method: Applied voltage or phase rotation meter.

e) No-Load (Open-Circuit) Loss Test

• Measures core losses (hysteresis & eddy currents).

• Test Method: Apply rated voltage to LV side with HV open.

• Acceptance Criteria: Within ±5% of factory test.

f) Short-Circuit (Impedance) Test

• Measures copper losses & impedance voltage.

• Test Method: Short HV, apply low voltage to LV.

• Acceptance Criteria: Within ±5% of nameplate.

g) Dielectric Tests (Insulation Strength)

• Power Frequency (50/60Hz) Withstand Test – Applied for 1 min.

• Impulse (Lightning) Test – For HV transformers (BIL rating).

2. Type Tests (For New Designs)

Performed on prototype transformers (not always on-site):

• Temperature Rise Test

• Lightning Impulse Withstand Test

• Partial Discharge (PD) Test

3. Special Tests (Optional/As Required)

a) Dissolved Gas Analysis (DGA) – For Oil Transformers

• Detects internal faults (overheating, arcing).

• Key Gases: H₂, CH₄, C₂H₂, CO, CO₂.

b) Sweep Frequency Response Analysis (SFRA)

• Detects winding deformation (shipping damage).

c) Tan Delta (Dissipation Factor) Test

• Measures insulation aging/moisture.

d) Bushing & OLTC (On-Load Tap Changer) Tests

• Contact resistance, timing, motor operation.

Acceptance Criteria & Documentation

✅ Compare results with factory test reports.
✅ Check compliance with IEC/IEEE standards.
✅ Verify nameplate data (kVA, voltage ratio, vector group).
✅ Ensure no physical damage (leaks, loose bolts).

The above content is published by demiks, please specify, demiks is a substation equipment manufacturer, specializing in the production of high-voltage tester, transformer test equipment, circuit breaker test equipment, relay tester, SF6 gas analyser, cable fault tester and other products, if you have power test testing needs, please feel free to contact demiks power science and technology limited company or send an email! Give us: contact@demikspower.com