Purpose of transformer turns ratio test

Transformer ratio testing is an important means of routine detection and fault diagnosis of transformers in power systems. Its main purposes include the following aspects:
1. Verify design parameters and manufacturing quality
Ensure that the turns ratio of the primary and secondary windings of the transformer meets the design specifications, and check for any errors in winding turns or connections during the manufacturing process.
Verify whether the gear of the tap changer is correct and whether the transformation ratio of each gear is within the allowable error range (usually within ± 0.5%).
2. Detecting winding faults
Interturn short circuit: If there is an inter turn short circuit in a certain phase winding, it will cause the actual transformation ratio to deviate from the theoretical value.
Winding open circuit or poor contact: Oxidation, looseness or winding disconnection of tap changer contacts can cause abnormal transformation ratio.
Winding deformation: Mechanical shock, overload, or short-circuit current may cause winding deformation, and the transformation ratio test can indirectly reflect such problems.
3. Evaluate the insulation health condition
Abnormal transformation ratio may reflect insulation degradation or partial discharge problems (such as winding insulation damage causing inter turn short circuits).
Combined with other tests such as winding DC resistance and no-load loss testing, the overall condition of the transformer can be comprehensively judged.
4. Ensure parallel operation conditions
When multiple transformers are connected in parallel, the transformation ratio must be strictly consistent, otherwise it will cause circulating current, increase losses, and even damage equipment.
Variable ratio testing can avoid voltage imbalance or circulating current problems caused by differences in variable ratios.
5. Fault diagnosis and preventive maintenance
Regular testing of transformers can detect early potential faults (such as aging tap changers and loose windings) and avoid sudden power outages.
After transformer maintenance or renovation, ratio testing is a key step in acceptance.
6. Meet the requirements of standards and specifications
International standards (such as IEC 60076), national standards (such as GB 1094), and industry regulations require transformer ratio testing before operation, after major repairs, or during regular maintenance to ensure equipment safety and reliability.