Cable withstand voltage test is a detection method for discovering cable faults. During the testing process, it is susceptible to various factors that may cause malfunctions, short circuits, and other issues. The following introduces the main methods of cable withstand voltage testing.
1、 Ultra low frequency withstand voltage test
The ultra-low frequency (0.1Hz) withstand voltage test method first appeared in 1980, mainly used as a non-destructive testing method to observe whether there are insulation defects in cables during operation. This method has been validated through extensive laboratory and field experiments, and the low-frequency withstand voltage test has shown good application results in the withstand voltage test of low-voltage power cables. This method utilizes the principle of converting 50Hz AC power into DC voltage through rectification and filtering, then converting the DC voltage into 1kHz AC voltage through an inverter circuit, and finally completing the amplitude modulation process with a 0.1Hz sine oscillator. After amplitude modulation, 1kHz AC voltage and other amplitude waves will become 0.1Hz amplitude waves. It is mainly based on the high voltage formed between the high voltage transformer and the voltage doubling circuit, mainly manifested as a sine wave, and mediated by a varistor to output a high voltage of 0.1Hz to the AC high voltage load. Voltage sine waveform. The advantages of ultra-low frequency withstand voltage test are: ① no damage; ② High precision; ③ The device has a small size and is easy to carry. But this method has a lower output voltage level and is mainly used for voltage withstand testing of medium and low voltage cables.
2、 Induction power frequency series resonance test
This method mainly utilizes the inductance of the reactor and the capacitance of the tested cable to generate resonance in a 50Hz power frequency environment, resulting in high voltage during this process. The advantages of tuning the power frequency series resonance test are: ① The output current waveform is basically a sine wave; ② High specificity, only when the series resonant circuit meets the conditions for resonance, will high voltage be formed. If there is a problem, the circuit will malfunction, equivalent to a cable short circuit, and the high voltage consistency will also decrease. Because the reactor can limit the short-circuit current and the protection device is not affected, there is no need to install a resistance protection device.
3、 Variable frequency series resonance test
The principle of frequency conversion series resonance test is similar to the principle of induction type power frequency series resonance test mentioned above. The only difference is that the variable frequency series resonance test achieves resonance in the test circuit by adjusting the output voltage frequency in the variable frequency power supply. The series resonance test is achieved in the test circuit by adjusting the inductance generated by the reactor at 50Hz power frequency to achieve resonance. The advantage of frequency conversion series resonance testing is that when the required power capacity for testing is lower than the power capacity of the tested cable, it can be tested at a power level far below the required power level, which can effectively improve the efficiency of on-site testing, overcome the shortcomings of adjustable power frequency withstand voltage testing devices, and make it more widely used in practical life. In addition, the working frequency of the variable frequency series resonance test is only 30-300Hz, which can solve the problem of low frequency and low loss in the ultra-low frequency withstand voltage test, and does not match the actual loss. Therefore, the results obtained from the frequency conversion series resonance withstand voltage test are accurate, comprehensive, and reliable.
Wuhan UHV specializes in the production ofseries resonance (also known as AC withstand voltage test equipment)and has been engaged in the electrical measurement industry for many years. Its products have first-class quality and welcome customers to come and purchase.
