By hvhipot 
HV Hipot Electric Co., Ltd. specializes in producing series resonance (also known as series resonance withstand voltage equipment). Next, we will share several main AC withstand voltage test methods with you.
Since the DC withstand voltage test cannot simulate the operating field strength state of cross-linked cables and cannot achieve the expected inspection effect, it is natural to turn to the AC withstand voltage test to assess the insulation condition of cross-linked cables. However, the biggest difficulty in using AC voltage tests at or near power frequency as the completion test for extruded insulated cable lines is that long lines require large capacity testing equipment. There are currently several methods for AC withstand voltage testing:
(1) Traditional test transformer with compensating reactor:
Due to the large capacity and high voltage of cables, traditional test transformers are no longer able to meet the requirements of on-site testing in terms of insulation, volume, weight, capacity, and other aspects; So cable testing rarely uses transformer testing.
(2) Oscillatory voltage test:
The oscillation voltage test is another way of testing the completion of extruded insulated cable lines by charging the cable with a DC power supply, causing the discharge gap to break down and discharge through an inductive coil when the test voltage is reached, and applying a certain voltage amplitude and frequency of kHz level attenuated oscillation wave voltage to the cable. This method is more effective than the DC withstand voltage test method, but compared with the power frequency voltage test, its effect on checking the main insulation and accessory defects of the cable is still not ideal.
(3) Ultra low frequency 0.1Hz withstand voltage test:
The equivalence of the 0.1Hz withstand voltage test still needs further research, and its effectiveness in detecting insulation defects is widely doubted worldwide. The current research results show that the breakdown voltage of insulation damage at 0.1Hz varies between 1.2-2.6 times the power frequency breakdown voltage, and there is a significant lack of consistency in the experimental results. At present, this method is mainly used for testing medium and low voltage cables, and the authenticity of the test conditions is not as good as that of near frequency AC voltage (30-300Hz). Due to the low voltage level, it cannot be used for testing high voltage cables of 110kV and above. From the perspective of application abroad, the current development direction of 0.1Hz is online insulation monitoring and fault location; The frequency conversion resonance method is used for voltage withstand testing, and its test equivalence is very good. From the perspective of foreign development, it is also recommended to use frequency conversion resonance method for voltage withstand testing.
(4) Series resonant withstand voltage test:
The series resonance test equipment forms a series resonance circuit with the test object (equivalent capacitance) to obtain a sine wave AC voltage of a certain frequency. Due to the high quality factor of experimental equipment, the required working power capacity is usually only a few tens of times the experimental capacity. For series resonance testing equipment, the system should meet the requirements of AC withstand voltage testing for different voltage levels and capacitance of the test samples within a certain frequency range. The resonance conditions can be met by changing the frequency or inductance.