By hvhipot 
HV Hipot Electric Co., Ltd. specializes in producing series resonance (also known as AC withstand voltage testing equipment). Next, we will share with you the methods for testing cable AC withstand voltage?
There are three methods for testing the AC voltage resistance of cables: cable testing ultra-low frequency method, cable testing oscillating voltage method, and cable testing resonant voltage resistance method. The detailed explanation is as follows.
Firstly, the ultra-low frequency method for cable testing. In ordinary power frequency withstand voltage testing, the cable capacity is relatively large, and the testing transformer capacity is also large, requiring a large amount of testing power supply on site to provide reactive power to the cable. Therefore, power frequency withstand voltage testing is not applicable in this field. Therefore, it is necessary to use ultra-low frequency as the testing power supply, which not only reduces the capacity of the testing transformer, but also makes on-site testing easier to operate. However, since the insulation defects detected by this method are not very effective, the term ‘method’ is commonly used in low-voltage cables applied in testing.
Next is the method of testing cable oscillation voltage. The principle of testing is to charge the cable with direct current. After the voltage reaches a certain value, the resistor and inductor are released through the gap to obtain damping oscillation voltage, in order to check the insulation defects of the main insulation and accessories of the cable. This method is more effective than DC withstand voltage testing, but there is attenuation in the oscillating voltage, which cannot meet the needs of long cables, and high-frequency voltage can cause significant damage to cables, which is a problem with this method.
Finally, there is the resonant withstand voltage testing method. This method can meet the testing requirements of high voltage and high current. According to the adjustment method, the resonant withstand voltage method is divided into inductance modulation method and frequency modulation method. According to the resonance mode, it can be divided into series resonance and parallel resonance. The adjustable inductance resonant withstand voltage of the cable is used to adjust the inductance of the loop reactor, so that the capacitor of the reactor and the cable resonate at the power frequency (50Hz) to meet the testing requirements.
The frequency modulation resonance withstand voltage of the cable is to change the output frequency of the test power supply, so that the reactor has a fixed inductance in the loop, and the tested product will resonate to meet the testing requirements. The cable series resonance method is to connect the reactor in series with the test product for testing when the current of the test transformer meets the testing requirements but the voltage does not reach the testing voltage.
When the circuit is in a resonant state, the test product can generate Q times (Q. The output voltage of the transformer is the quality factor of the loop). The energy supplied by the power supply is only the active power consumed in the loop. The cable parallel resonance method is to connect the reactor in parallel with the test product when the voltage of the test transformer meets the test requirements but the current does not meet the requirements, so that the loop parameters meet the resonance requirements of the test. The induced current of the reactor compensates for the capacitive current of the test product.