Transformer handover tests are a crucial step to ensure the safe operation of newly installed or overhauled transformers. The test items, corresponding equipment, and execution standards are all clearly defined, with the core reference being GB 50150-2016 “Code for Handover Test of Electrical Equipment in Electrical Installation Projects”. The following is a detailed classification description.
I. Main Handover Test Items, Test Equipment and Standard Requirements
Measurement of DC Resistance of Windings
The core test equipment is a DC resistance tester (micro-ohmmeter). The standard requirements are as follows: For three-phase transformers of 1600kVA and below, the mutual difference of the resistance values of each phase winding should not exceed 4% of the average value; the mutual difference of the resistance values between lines should not exceed 2% of the average value. For three-phase transformers above 1600kVA, the mutual difference of the resistance values of each phase winding should not exceed 2% of the average value; the mutual difference of the resistance values between lines should not exceed 1% of the average value. Compared with the measured values at the same temperature when the product left the factory, the change should not exceed 2%.
Measurement of Insulation Resistance, Absorption Ratio or Polarization Index of Windings
The core test equipment is an insulation resistance tester (megohmmeter), which should match the corresponding voltage level. For example, a 2500V megohmmeter is used for 10kV transformers, and a 5000V megohmmeter is used for 220kV transformers. The standard requirements are as follows: The insulation resistance value should not be less than 70% of the factory test value. For transformers with a voltage level of ≥6kV, the absorption ratio (R60/R15) should be measured, and the absorption ratio should not be less than 1.3; the polarization index (R10min/R1min) should not be less than 1.5. This requirement applies to oil-immersed transformers.
Measurement of Dielectric Loss Factor (tanδ) of Windings
The core test equipment is a dielectric loss tester. The standard requirements are as follows: For oil-immersed transformers at 20℃, the tanδ value should not exceed 0.015 (for 10kV level) or 0.010 (for 35kV and above). Compared with the factory value, the change should not exceed 30%.
AC Withstand Voltage Test
The core test equipment is a power frequency withstand voltage test device, consisting of a test transformer, a voltage regulator, and a protective resistor. The standard requirements are as follows: The test voltage should be executed according to the provisions in GB 50150-2016. For example, the handover withstand voltage of a 10kV oil-immersed transformer is 35kV, with a duration of 1 minute. There should be no breakdown or flashover during the test.
Measurement of Transformation Ratio
The core test equipment is a transformation ratio tester. The standard requirements are as follows: The deviation of the transformation ratio from the nameplate value should not exceed ±0.5%. When measuring at each tap position of the tap changer, the transformation ratio should meet the technical requirements.
Measurement of Three-Phase Connection Group or Single-Phase Polarity
The core test equipment is a transformation ratio tester or polarity tester. The standard requirement is that the connection group or polarity should be consistent with the nameplate marking, with no errors.
Measurement of No-load Current and No-load Loss
The core test equipment is a no-load test bench, consisting of a power analyzer and a voltage regulator. The standard requirements are as follows: The deviation of the no-load current from the factory value should not exceed ±30%. The deviation of the no-load loss from the factory value should not exceed ±15%.
Measurement of Short-circuit Impedance and Load Loss
The core test equipment is a load test bench. The standard requirement is that the deviation from the factory value should not exceed ±10%.
Insulation Oil Test
The core test equipment includes an oil dielectric loss tester, a breakdown voltage tester, and a chromatographic analyzer. The standard requirements are as follows: For breakdown voltage, it should be ≥35kV for 10kV level and ≥40kV for 35kV level. For chromatographic analysis of dissolved gases in oil, there should be no acetylene (C₂H₂), and the total hydrocarbon content should comply with the standard.
Measurement of Insulation Resistance of Core (Clamp)
The core test equipment is a 2500V megohmmeter. The standard procedure requires that the insulation resistance value of the core to ground should not be lower than 10MΩ, and the insulation between the core and the clamping piece should be good.
II. Key Notes for Test Execution
Test Sequence
The principle of “non-destructive tests first, then destructive tests” should be followed. For example, measure the insulation resistance and DC resistance first, and then conduct the AC withstand voltage test to avoid equipment damage due to potential defects during the withstand voltage test.
Temperature Correction
Test results such as DC resistance and dielectric loss need to be converted to the same reference temperature, usually 20℃, and then compared and analyzed with the factory value or standard value.
Special Transformer Requirements
The test standards for dry-type transformers and gas-filled transformers are slightly different. The corresponding chapters in GB 50150-2016 should be referred to for execution.
Post time: Jan-08-2026