The test results of series resonance are sometimes affected by uncertain factors. These uncertain factors include:
1. The influence of weather
In the case of high humidity, the corona loss of the lead wire is greatly increased, and the interference of the surrounding electromagnetic field also increases, causing the Q value to decrease.
2. the influence of test time
With the extension 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 the summer, and often the equipment needs to rest for 30 minutes before continuing to use it.
3. the influence of reactor
If the reactor is placed on metal parts such as iron plates, eddy current loss is formed and the equivalent resistance increases.
4. The influence of high-voltage test frequency on Q value if a better resonance point is not selected
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 action and the test must be restarted. This is detrimental to 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 after that, the test voltage should not exceed 40%. In this case, adjust the frequency again, and a little bit lower, to avoid the above phenomenon.
5. The influence of high voltage leads
When the AC withstand voltage test of a single electrical equipment is performed, due to the small capacitance of the test product, the high-voltage lead has little effect on the test. When the AC withstand voltage test can be performed on the outdoor power distribution device as a whole, the installation height of the equipment increases with the voltage level. The higher the voltage level, the longer the high-voltage lead. Generally, the high-voltage lead is longer, the corona loss is increased, and the equivalent resistance in the loop increases. The stray capacitance formed by it is connected in parallel to the measured capacitance. 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. Make the Q value drop. Therefore, when conducting the AC withstand voltage test of high-voltage electrical equipment, try to use the corrugated tube high-voltage lead.