1. Full Name & Function of Each Parameter
IR – Insulation Resistance
Insulation Resistance tests the DC insulation resistance between transformer windings to ground and between different windings. It is the fundamental test for judging insulation conditions. A high resistance value means dry and sound insulation, whereas a noticeable drop generally originates from damp insulation, surface dirt or mechanical damage to insulating paper and materials. It is widely used for quick preliminary insulation screening during equipment handover, overhaul acceptance and daily routine inspections.
TTR – Transformer Turns Ratio
The Transformer Turns Ratio test compares the actual measured winding ratio with the theoretical rated ratio on the transformer nameplate. Excessive ratio deviations are clear signs of inter-turn short circuits, bad contact of tap changers, broken winding wires and abnormal magnetic core performance. This mandatory test prevents magnetic flux imbalance, abnormal local overheating and even transformer burnout, playing a critical role in factory delivery inspection and post-fault maintenance verification.
WR – Winding Resistance
Winding Resistance measures the DC resistance of each transformer winding. Test data is used to check for loose winding joints, broken strands, poor connection at lead terminals and abnormal contact inside tap switches. Unbalanced resistance among three phases will generate extra heat loss during operation, accelerating insulation aging. It is an indispensable electrical test to verify the integrity of winding conductive circuits after production, maintenance or field installation.
BDV – Breakdown Voltage
Breakdown Voltage reflects the ultimate dielectric strength of transformer insulating oil, representing the critical voltage value at which oil insulation will be punctured. Dissolved moisture, suspended particles and oil aging pollutants will directly lower BDV values and raise the risk of internal arc discharge and equipment breakdown. BDV serves as the most direct physical benchmark to evaluate the quality and insulation performance of transformer oil.
2. Comprehensive Value of the Five Testing Indicators
As key backbone equipment for power transmission and distribution systems, oil-immersed transformers suffer from insulation aging, conductive circuit faults and oil deterioration when enduring long-term thermal load, high electric field stress and complex operating environments. The combined test set of IR, TTR, Winding Resistance and BDV builds a complete transformer health evaluation system, covering winding conductive structure, winding turn matching, solid insulation performance and liquid insulation quality in all dimensions.
WR and TTR jointly secure the physical and electrical integrity of transformer windings; IR and Tan Delta monitor both apparent and recessive deterioration of solid insulation; BDV assesses the safety performance of insulating oil matched with other oil-related tests. With regular detection using these five parameters, power operators can shift maintenance mode from passive breakdown repair to proactive condition-based maintenance. This standardized testing solution complies with global IEC and IEEE specifications, effectively prolonging transformer service life and ensuring stable, safe operation of the whole power grid.