Transformer test method

A) Test wiring

AC withstand voltage test wiring is applied outside the small and medium-sized power test transformers below 35kV. All windings should be tested. When testing the transformer, the lead wires of each phase winding should be shorted together, and the lead wires with lead wires at the neutral point should also be shorted together with the three phases.

2) Test voltage

The handover test specification stipulates that transformers with a capacity of less than 8000kV and a winding rated voltage of less than 110kV shall be subjected to an AC withstand voltage test in accordance with the test voltage specifications listed in Appendix 1 of the specification.

The preventive test regulations stipulate: the test voltage value of oil-immersed transformer is detailed in the regulation table (regular test is according to the voltage value of partial winding). When all windings of dry-type test transformer are replaced, the value of the factory test voltage shall be used; for partial winding and regular test, press 0.85 times the value of the factory test voltage.

Precautions for transformer test

In addition to the general AC withstand voltage test precautions, the following points should be noted according to the characteristics of the transformer:

1. The test transformer must be equipped with an overcurrent maintenance trip device.

2. The AC withstand voltage test of the three-phase transformer does not need to be carried out in phases. However, it is necessary to short-circuit all the lead wires of the three phases of the unified winding before performing the test, otherwise it will not only affect the accuracy of the test voltage, but may even endanger the main insulation of the transformer.

3. The preventive test regulations point out that for fully insulated transformers below 66kV, when the site conditions are not available, only the external construction frequency withstand voltage test can be carried out.

4. For power transformers whose neutral point insulation is weaker than other parts or graded insulation, the above external AC withstand voltage test cannot be used, but an induction withstand voltage test of 1.3 times the rated voltage should be used.

5. It must be tested after being filled with qualified oil and resting for a certain period of time.

6. The voltage level is 35kV medium and small capacity transformers, allowing the test voltage to be measured on the low-voltage side of the test transformer. For power transformers with larger capacity, in order to make the measurement accurate and reliable, a voltage transformer or electrostatic voltmeter should be used on the high-voltage side. Directly measure the test voltage.

7. If discharge or breakdown occurs during the test, immediately lower the voltage and cut off the power supply to avoid expanding the fault.