How to analyze the test results when using the test transformer for AC withstand voltage test:

1. Test transformer

Oil-immersed test transformer, gas-filled test transformer, dry-type test transformer

The test transformer is the most commonly used equipment in the current power system for the insulation strength test of various high-voltage electrical equipment and insulating materials at power frequency or DC high voltage. The developed oil-immersed test transformer has small size, light weight, compact structure and full functions. , With the characteristics of strong versatility, simple use and convenience, conventional test transformers can be divided into oil-immersed test transformers, gas-filled test transformers, and dry-type test transformers according to the insulating medium.

2. AC withstand voltage test

AC withstand voltage test is the most effective and direct method to identify the insulation strength of power equipment

AC withstand voltage test wiring

The test voltage used in the AC voltage test is much higher than the operating voltage. Excessive voltage will increase the loss of the insulating medium, heat, and discharge, and will accelerate the development of insulation defects. Therefore, in a sense, the AC resistance Compression test is a destructive test, so it can effectively find insulation defects. Therefore, the AC withstand voltage test has become an important means to ensure safe operation.

3. Analyze the test results

Under normal circumstances, during the AC withstand voltage test, the test product is considered qualified without breakdown, otherwise it is considered unqualified. Specific analysis and judgment are made through the following situations

(1) Judging by the change of the meter indication: the indication of the ammeter connected to the test circuit increases suddenly and greatly, generally indicating breakdown or partial discharge. In addition, the indication of the high-voltage side voltmeter suddenly drops significantly, which is also regarded as a test. Product breakdown.

(2) Judging by the action of the electromagnetic switch of the control circuit on the low-voltage side of the test transformer: If the over-current relay on the test circuit on the low-voltage side of the test transformer is properly set, then when the test product breaks down, the relay will act due to the excessive current. The switch is tripped, so the breakdown of the test product can be judged by the trip of the electromagnetic switch. However, attention should be paid to distinguish whether the capacitance current of the test product during the boosting process is too large due to the setting value being too small, or the setting value is large, even if the test product is discharged or a local small current is broken down, The switch does not necessarily trip and so on. Therefore, the behavior of the electromagnetic switch should be analyzed in detail.

(3) Judging by other abnormal conditions that occurred during the withstand voltage test: If the voltage is boosted or smoke, outgassing, burnt odor, arc flash discharge, etc. occur within the specified withstand voltage time, it indicates that the insulation is defective.

(4) Judging by the insulation resistance value before and after the withstand voltage: the insulation resistance of the equipment with good insulation before and after the withstand voltage should not be clear, otherwise the cause should be investigated

(5) Heat generation after the test product has withstand voltage: A well-insulated device should not generate heat after it has withstand voltage, otherwise the cause should be found out. Attention should be paid to the flashover caused by the surface of the tested product being damp, dirty, etc. In order to avoid this situation, the external insulation of the sample should be treated before the test to avoid misjudgment.