Transformer Insulation Resistance Test
Electrical Engineering| Published Date:
6 July 2025
Kyaw Myo Oo
Insulation resistance (IR) testing is a vital step in assessing the condition of transformer windings. This test ensures the windings are properly insulated and free from moisture, contamination, or deterioration that could lead to insulation failure. Here's a step-by-step guide:
⚠️ Safety First
Before performing the test, ensure the transformer is completely de-energized and isolated. Use appropriate personal protective equipment (PPE) and follow site-specific safety protocols.
Step by Step Procedure
1) Isolate the Windings
- Disconnect all internal and external connections to the transformer windings.
2) Discharge Stored Charges
- Discharge the windings to ground to eliminate any residual voltage. This is critical to avoid inaccurate readings and ensure operator safety.
3) Apply Test Voltage
- Use a 5kV DC insulation tester.
- For the first test, apply voltage between 22kV Primary winding and Earthing, test voltage set to 5kV DC. (see below connectoin diagram)
4) Apply Test Voltage
- Monitor the Megger meter and record the IR reading at the 60 second mark.
5) Power Down the Megger
- After the reading is taken, turn off the Megger and safely discharge the winding again.
6) Repeat the Test
Perform the same test on the following combinations:
- Primary to Secondary winding
- Secondary winding to Earth