The AC series resonance test system under UHV power can help many power workers conduct various power tests more conveniently.

The power frequency AC withstand voltage test is to apply a certain voltage to the test object and maintain it for a certain period of time, in order to consider the ability of the insulation of the test object to withstand various voltages and ensure the safe operation of the equipment. Although insulation resistance and absorption ratio tests, leakage current and DC withstand voltage tests, and dielectric loss angle measurement tests can detect many insulation defects, they often cannot be detected in a timely manner due to their test voltage being lower than the working voltage of the tested object. In order to further expose equipment defects, check the insulation level of electrical equipment, and ensure whether it can be put into operation, it is necessary to conduct AC withstand voltage tests. It is the most effective and direct method for assessing the insulation strength of electrical equipment, and it has decisive significance in determining whether electrical equipment can be put into operation. The voltage, waveform, frequency, and distribution of voltage inside the insulation of the tested object in the AC withstand voltage test are consistent with the actual operating conditions. Therefore, AC withstand voltage can effectively detect the more dangerous concentrated defects in electrical equipment. The higher the test voltage, the more effective it is to discover insulation defects, but the greater the possibility of the tested object being broken down. For samples with good insulation, AC withstand voltage will gradually weaken the insulation strength, resulting in the accumulation effect of poor insulation quality inside. The value of insulation breakdown voltage is not only related to the applied voltage, but also to the duration of the pressurization, and its breakdown voltage gradually decreases with the increase of pressurization time. Therefore, it is necessary to correctly select the standard of test voltage and withstand time. The current standard stipulates a withstand voltage time of 1 minute, on the one hand, to facilitate observation of the condition of the test sample and allow time for weak insulation to be exposed, especially for solid insulation that requires a certain amount of time for thermal breakdown; On the other hand, it will not cause unnecessary breakdown due to prolonged time.

Experimental operation method

1) Overcurrent protection setting: Set the low-voltage current relay and high-voltage current relay in the control panel separately, generally set to 1.1 times the test current.

2) Overvoltage protection setting: Set to 1.1 times the voltage during the test.

Example: When the test voltage is 45kV, the display should be adjusted to 47kV.

3) Connect the shielding wire of the voltage divider to the two high-voltage terminals on the control console. Note that all ground wires must be securely and reliably connected.

4) Connect the high-voltage currents K1 and K2 on the excitation transformer to the high-voltage current terminals on the control panel

5) Voltage endurance time setting: Set the test time on the time relay to the desired test time.

6) Connect the test wiring as shown in the diagram and check for errors before closing.

7) Close the circuit breaker on the control panel. If the voltage regulator is not in the zero position, it will automatically return to zero. The test can only be conducted after the regulator returns to zero.

8) Generally, before the main power supply is not connected, adjust the reactor core clearance, and observe whether the lifting and clearance limit protection functions are normal. In addition, it is possible to adjust the boost and buck appropriately, and observe whether the button and low-voltage voltage meter are working properly.

Precautions for the operation process of power frequency withstand voltage test:

a、 Test personnel should divide responsibilities, set a safe distance at the test site, carefully inspect the grounding of the test sample and test transformer, and assign a dedicated person to monitor safety and observe the status of the test sample.

b、 The main parts of the test sample should be cleaned thoroughly and kept absolutely dry to avoid damaging the test sample and causing errors in the test values.

c、 For the testing of large equipment, it is generally necessary to first conduct a no-load test of the test transformer, that is, to increase the voltage to the test voltage without connecting the test sample, in order to calibrate the accuracy of the instrument indication and adjust the ball spacing of the discharge ball gap.

d、 When conducting a voltage withstand test, the boosting speed should not be too fast, and sudden pressure should be prevented. For example, if the regulator is not at zero position, it should be suddenly closed, and the power should not be suddenly cut off. Generally, it should be closed when the regulator drops to zero position.