What are the tests for mining transformers?

Our factory tests are conducted according to IEC60076 standards to ensure the transformer meets the required specifications and operational performance.

mining transformer includes the following routine tests:

• Winding Resistance Measurement HV and LV
• Insulation Resistance Test HV to earth, LV to earth and HV to LV
• Voltage Ratio Test and Vector Group Verification
• No-Load Loss and No-Load Current Test
• Load Loss and Impedance Voltage Test
• Separate-source Power Frequency Voltage withstand test
• Induced Overvoltage
• Leakage Test of transformer Tank and Accessories

1. Winding Resistance Measurement (HV and LV)

Winding resistance measurement for both high-voltage (HV) and low-voltage (LV) windings is a fundamental test to detect issues such as poor connections, short circuits, or conductor damage. To conduct this test:

1. Procedure: Use a low-resistance ohmmeter to measure the resistance of the windings at both HV and LV levels. Follow standard procedures to ensure accurate readings.
2. Specifications: Ensure that the resistance unbalance between phases is ≤ 2%. An unbalance greater than 2% could indicate issues with winding integrity or loose connections.

Regularly performing this test helps verify the mechanical stability and electrical continuity of transformer windings.

2. Insulation Resistance Test

Insulation resistance testing assesses the health of the insulation material, detecting signs of moisture ingress, aging, or deterioration. Proper insulation is crucial to prevent short circuits and maintain dielectric strength.

1. Procedure: Use a megohmmeter to measure the resistance between the windings and the transformer core or ground.
2. Evaluation: Check whether the insulation material is damp or aged. Reduced insulation resistance suggests that the insulation may have absorbed moisture or experienced degradation over time. Any irregularities should be investigated immediately to avoid potential breakdowns.

3. Voltage Ratio Test and Vector Group Verification

The voltage ratio test confirms that the transformer's voltage transformation aligns with its design specifications, while vector group verification ensures proper phase relationships.

1. Procedure: Measure the voltage ratio at each tap position, using a digital voltmeter or transformer turns ratio (TTR) tester.
2. Specifications: The voltage ratio error should not exceed 0.5% of the specified value.
3. Vector Group Verification: Validate that the phase displacement and vector group (such as Dyn11 or Yyn0) match design requirements.

These checks ensure that the transformer will perform reliably in a connected network, maintaining correct phase relationships and voltage ratios. The power supply capacity that the transformer can really load during load operation.

4. No-Load Loss and No-Load Current Test

This test measures the losses and current drawn by the transformer when no load is connected, helping to evaluate core performance and design efficiency.

1. Procedure: Apply rated voltage to the transformer primary winding with the secondary winding open. Measure the power consumed (no-load loss) and the current drawn (no-load current).
2. Evaluation: High no-load losses indicate core issues such as high eddy currents or poor-quality core material, while high no-load current can suggest core saturation or magnetizing issues.

No-load tests are essential to optimize transformer efficiency and reduce core-related energy losses.

5. Load Loss and Impedance Voltage Test

To measure load losses and impedance voltage. Gradually increase voltage on HV side until rated current flows. Keep LV side short-circuited. Apply rated current and measure load losses and impedance at145°C.

Load loss and impedance voltage tests assess the transformer's performance under typical operating conditions and ensure it can handle the expected load without excessive energy losses.

1. Procedure: Connect a known load or apply short-circuit conditions to the secondary winding while measuring the load losses and impedance voltage.
2. Specifications: Load losses should align with the transformer's rating. Any significant deviation could indicate issues with winding or core design.

6. Separate-source Power Frequency Voltage Withstand Test

This high-voltage test checks the insulation strength of the transformer by applying an external voltage source, ensuring it can withstand operational stresses without breakdown.

1. Procedure: Apply a power frequency voltage between windings and ground, typically for 60 seconds, to test insulation robustness.
2. Evaluation: Ensure no partial discharges or breakdowns occur during the test. Any insulation failure indicates potential weak points that must be addressed.

Withstand testing confirms the transformer's readiness for high-stress environments and ensures long-term durability of its insulation system.

7. Induced overvoltage withstand test

To check insulation integrity against overvoltage conditions, apply twice the rated voltage at higher frequency for 40 seconds.

8. Leakage Test of Transformer Tank and Accessories

To ensure no leak is present. Pressurize the transformer at least 50KPa at constant temperature and observe for leaks over 48 hours.

Mining transformer’s tank and accessories must be leak-proof to prevent the ingress of moisture and other contaminants, which could damage the insulation and core materials.

1. Procedure: Pressurize the tank and examine for signs of leakage in the joints, bushings, and gaskets.
2. Evaluation: Any leaks identified should be sealed immediately to maintain the transformer's integrity and extend its lifespan.

Conclusion

Proper transformer testing is vital for ensuring the operational safety, reliability, and efficiency of these power assets. From winding resistance and insulation testing to more advanced partial discharge and thermal stability evaluations, each test provides critical data on the transformer's condition and suitability for service. By adhering to stringent testing protocols, operators and maintenance teams can prevent premature failures, reduce downtime, and extend the transformer's useful life. Implementing these tests as part of a regular maintenance program is key to ensuring your transformers operate at peak performance for years to come.