The purpose of the AC withstand voltage test
The AC withstand voltage test is the most effective and direct method for evaluating the insulation strength of power equipment. During the operation of power equipment, the insulation is constantly subjected to the effects of electric fields, temperature and mechanical vibrations, which will gradually deteriorate, including overall deterioration and partial deterioration, resulting in defects.
Various preventive testing methods each have their own advantages, and they can respectively detect some defects and reflect the condition of insulation. However, the test voltages of other testing methods are often lower than the working voltage of power equipment. But the AC withstand voltage test is generally higher than the operating voltage. Therefore, through testing, it has become an important means to ensure the safe operation of transformers.
Test subjects
The AC withstand test of the windings together with the bushings shall comply with the following provisions:
For transformers with a capacity of less than 8000 kVA and a rated winding voltage of less than 110 kV, the terminal tests should be conducted according to the standard procedures for performing AC withstand voltage tests.
2. For transformers with a capacity of 8000 kVA or more and a rated winding voltage of 110 kV or below, when there is testing equipment available, the line-end AC withstand voltage test can be conducted in accordance with the voltage test standards listed in Table 1.
3. For transformers with a rated voltage of 110 kV or higher, the neutral point should undergo an AC withstand voltage test. The test withstand voltage standard is 80% of the factory test voltage value.
Preparations for the experiment
1) Fill out the work ticket, prepare the operation control card and quality control card, and complete the work permit procedures for the team.
2) Inform the team members of potential hazards, explain the work content, personnel division, and live parts. After completing the confirmation procedures, start the work.
3) Prepare the test equipment, instruments and tools. The instruments and meters used are in good condition and are within the valid period.
4) Inspect the transformer casing. It should be reliably grounded.
5) Use the insulated operating rod to bring the grounding wire up and discharge the energized parts of the transformer.
6) After the discharge is completed, remove the high-voltage, medium-voltage and low-voltage leads of the transformer, and all other workers should evacuate the site.
7) Inspect the appearance of the transformer and clean off any surface dirt.
8) Connect the power supply. First, check whether the power supply voltage meets the experimental requirements. The power cord must be firmly connected to prevent sudden disconnection. Also, verify if the leakage protection device operates sensitively.
9) A test fence will be set up around the test site and dedicated personnel will be assigned to guard it.
Equipment and materials required for the experiment:
High Voltage Test Control Box
Inflatable test transformer
Protective gap
Capacitive-resistive voltage divider
Protect water resistance
High-voltage lead wire
Grounding wire
Discharge rod
Humidity and temperature gauge
Fence
Warning sign
Post time: Jul-16-2026