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The AC withstand voltage plays a decisive role in assessing the main insulation strength of transformers and checking for local defects in the main insulation. It is an important means of checking and verifying the quality of transformer design, manufacturing, and installation.

Scope of AC withstand voltage test

1. For transformers with a capacity of 8000KV or less and a rated winding voltage of 110KV or less, an AC withstand voltage test should be conducted for the terminal test.

2. Transformers with a capacity of 8000KV. A or above and a rated winding voltage of 110KV or below can undergo terminal AC withstand voltage testing when equipped with testing equipment.

3. For transformers with a rated winding voltage of 110KV or above, the neutral point should undergo an AC withstand voltage test, and the test withstand voltage standard is 80% of the factory test voltage value.

Basic methods for testing high voltage in communication experiments

1. Adopt the method of testing the low voltage side voltage of the transformer and then converting it into the high voltage side test voltage. This method is suitable for test samples with small capacitance, such as insulators, switches, and other equipment. For test samples with large capacitance, capacitive loads can cause the actual output voltage on the high voltage side of the transformer to be much higher than the theoretical calculation, so they are not suitable for use.

2. Method for measuring the high voltage side voltage of a test transformer using a voltage transformer. The primary side of the voltage transformer TV is associated with the test object, and the high voltage is converted into low voltage using the voltage transformer. The accurate level of the voltmeter is used to measure it, and then the test voltage value on the high voltage side is converted based on the transformer ratio. The secondary method is simple and accurate, but requires a voltage transformer with corresponding measurement voltage level.

3. The method of directly measuring the high voltage side voltage of the test transformer using an electrostatic voltmeter.

4. Method of measuring high voltage in AC test using standard ball gap.

This method directly measures voltage amplitude with high accuracy and a wide measurement range within a certain range; But each measurement must be discharged, the measurement time is long, and there are many factors that are affected, so this measurement method is often limited to laboratory use.

Precautions for AC withstand voltage test

1. AC withstand voltage is a destructive test, so the tested object must pass various insulation tests such as insulation resistance, absorption ratio, and insulation oil spectrum before the withstand voltage test and be qualified. Each oil filled equipment should be allowed to stand still for sufficient time after oil injection before being pressurized, in order to avoid unnecessary insulation breakdown caused by pressure resistance.

2. When conducting a pressure test, the temperature of the test object should not be lower than 5 ℃. Outdoor tests should be conducted in good weather, and the relative humidity of the air should generally not exceed 80%.

3. During the experiment, the test personnel should communicate clearly with each other, and there should be someone to supervise during the pressurization process.

4. During the pressurization period, close attention should be paid to the dynamic indication of the meter to prevent resonance phenomenon from occurring; Attention should be paid to observing and monitoring the sound and phenomena of the tested transformer and protective ball gap, and analyzing and distinguishing relevant signs such as corona or discharge.

5. Sometimes the withstand voltage test lasts for tens of seconds, and if the power supply is lost midway, the test terminal may be affected. After identifying the cause and restoring the power supply, a full time continuous withstand voltage test should be conducted again, rather than just a "make-up time" test.

6. The quality factor Q value of resonance test bribery is related to the dry and clean surface of the test equipment and the insulation of the test sample, as well as the diameter and length of the high-voltage lead. Therefore, the test should be conducted in sunny weather. The experimental equipment and video insulation surface should be dry and clean. Try to shorten the length of high-voltage leads as much as possible and use large-diameter high-voltage leads to reduce corona losses. Improve the quality factor Q value of the test circuit.

7. The grounding terminal of the transformer and the grounding terminal of the measurement and control system should be connected to each other and form their own circuit. A single point grounding method should be used, that is, only one point should be connected to the grounding terminal of the grounding grid.