Even with the so-called “all-powerful” series resonance, the test results will still be affected by uncertain factors, including:

1. The influence of weather

In the case of high humidity, the corona loss of the lead wire increases greatly, and the interference of the surrounding electromagnetic field also increases, which makes the Q value decrease.

2. The influence of test time

With the prolongation of the test time, the equipment is heated, the equivalent resistance increases, and the Q value also shows a downward trend. This phenomenon is very obvious in hot weather, and often the equipment needs to be rested for 30 minutes before it can continue to be used.

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3. The influence of the reactor

If the reactor is placed on metal parts such as iron plates, eddy current loss will be formed and the equivalent resistance will increase.

4. The effect of not selecting a better resonance point for the high-voltage test frequency on the Q value

In the application, it is found that when the voltage rises close to the test voltage, the voltage rises too fast and is accompanied by large voltage fluctuations, which can even cause the voltage protection to operate, so that the test must be restarted, which is not good for the safety of the equipment, but If the voltage protection value is set too large, it will not be able to protect the equipment under test from overvoltage. Therefore, it is generally adjusted to a better resonance frequency at 2% of the test voltage, and then at no more than 40% of the test voltage If necessary, adjust the frequency again, and make it slightly smaller to avoid the above phenomenon.

5. The influence of high voltage leads

When a single item of electrical equipment is subjected to an AC withstand voltage test, due to the small capacitance of the test product, the high-voltage lead wire has little influence on the test. When the AC withstand voltage test can be carried out on the whole outdoor power distribution device, the installation height of the equipment increases with the voltage level. The higher the voltage level, the longer the high-voltage lead wire. Generally, the high-voltage lead wire is longer, the corona loss is enhanced, and the equivalent resistance in the loop is increased. The stray capacitance formed by it is connected in parallel to the measured capacitance, and the resonance frequency of the loop decreases, which makes the Q value decrease; at the same time, the interference of the surrounding electromagnetic field also increases. It makes the Q value drop. Therefore, when performing the AC withstand voltage test of high-voltage electrical equipment, try to use the bellows high-voltage lead.

Therefore, in the AC withstand voltage test, in addition to relying on the good performance of series resonance, attention should also be paid to voltage equalization measures, such as: reasonable selection of wires, reasonable layout of the test site, reasonable arrangement of time, etc., and heat dissipation and dehumidification can also be taken. The method reduces the influence on the Q value when the equipment is heated and damp.