IR Value Testing of Power Transformers
Insulation Resistance (IR) testing is a critical diagnostic procedure used to assess the insulation condition of power transformers before commissioning and during maintenance.
Using an insulation resistance tester (Megger), technicians measure insulation resistance between HV and LV windings, HV winding and earth, and LV winding and earth, as applicable to the transformer design and test procedure.
Test results are typically recorded at specified test voltages and durations, including 1-minute readings and, where appropriate, 10-minute readings for Polarization Index (PI) assessment. Results must be interpreted with consideration of transformer temperature, humidity, insulation type, previous test records, and manufacturer recommendations.
IR testing helps identify potential insulation deterioration, moisture ingress, contamination, and other abnormalities. However, IR values alone cannot confirm the complete health of a transformer; they should be evaluated alongside other diagnostic tests and historical trends.