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Withstand voltage test steps and result judgment

time:2021/1/29   source:华天电力  reading:275 time

Pressure test steps for oil-immersed test transformers

During the test, the following steps should be strictly followed to ensure the correct judgment of the test results and the safety of the test process.

1. Connect the test clips of the test equipment to the specified test parts (two or more parts isolated from each other such as transformer winding, shield, iron core, frame, etc.).

2. Check whether the test equipment is placed in the voltage gear required for the test, and whether the set leakage current value meets the requirements.

3. Short-circuit the high-voltage output terminal of the test equipment, and check whether the overcurrent relay operates or sends out a breakdown signal.

4. Check the test environment for unsafe factors. If not, turn on the pressure equipment to preheat for 5 minutes.

5. Operate the test equipment to increase the pressure. At the beginning of the boost, slowly increase to half of the specified value (jump should be avoided), and then quickly increase to the specified voltage value (the entire boost process is about 10s), which lasts for 1 min, during which continuous arcing and breakdown are not allowed When the phenomenon occurs, slowly return the voltage to zero, cut off the power supply, and the test is completed.

Hipot Test Set.png

Keep in mind that sudden power-off methods are not allowed to prevent the transformer from breakdown due to oscillation overvoltage caused by instantaneous voltage loss.

Judgment Method of Test Results of Oil-immersed Test Transformer

If a voltage drop or breakdown signal occurs during the test, do not judge the breakdown of the transformer easily at this time. Further testing should be continued to make further confirmation:

1. If the insulation resistance does not change much, or there is no breakdown action for 1 min after the second boost, the first breakdown is considered to be an air gap breakdown, which is usually called flashover. After the applied voltage disappears, the breakdown gap immediately recovers by itself, the insulation resistance of the transformer does not change, and the insulation performance of the transformer does not change, so it cannot be judged as unqualified.

2. Measure the insulation resistance with a megohmmeter. If the insulation resistance is zero or close to zero, it is judged as a breakdown; or conduct a secondary boost test, and the voltage is gradually applied. If it is a breakdown, when the voltage is increased to a certain value , If continuous spark discharge or heat and smoke can be observed near the breakdown point, it is judged as breakdown. If the second pressure is applied, the voltage rises and falls again, and the pointer of the ammeter swings violently, it is judged that the arcing is not qualified.

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