There are three main methods for conducting AC withstand voltage tests on series resonance (also known as resonance devices): ultra-low frequency test method, oscillation voltage test method, and resonance withstand voltage test method.

Experimental ultra-low frequency method

Due to the large capacity of cables and transformers in commonly used power frequency withstand voltage tests, as well as the need for a considerable on-site test power supply to provide reactive power to the cables, the power frequency withstand voltage test is not suitable for the site. Therefore, ultra-low frequency is needed as the test power supply, which not only reduces the capacity of the test transformer, but also simplifies the on-site test operation. However, due to the poor insulation defect detection effect of this method, it is generally applied in medium and low voltage cable tests.

Experimental oscillation voltage method

The experimental principle is to charge the cable with DC, and after the voltage reaches a certain value, discharge the resistor and inductor through the gap to obtain a damping oscillation voltage, which can be used to check the insulation defects of the main insulation and accessories of the cable. This method is more effective than the DC withstand voltage test, but the oscillation voltage attenuates and cannot meet the needs of long cables. In addition, high-frequency voltage can cause significant damage to the cable, which is a problem with this method.

Resonant voltage withstand test method

This method can meet the testing requirements of high voltage and high current. The resonant withstand voltage method is divided into inductive and frequency modulation according to the adjustment method, and series resonance and parallel resonance according to the resonance method. Inductive resonant withstand voltage is achieved by adjusting the inductance of the circuit reactor, so that the capacitance of the reactor and the cable resonate at the power frequency (50Hz) to meet the testing requirements; Frequency modulation resonant withstand voltage is to change the output frequency of the test power supply, so that the fixed inductance reactor in the circuit resonates with the test sample to meet the test requirements.

Series resonance is a test method in which a reactor is connected in series with the test sample when the current of the test transformer meets the test requirements but the voltage does not reach the test voltage. When the circuit is in resonance, Q times (Q is the quality factor of the circuit) of the transformer output voltage can be generated on the test sample, and the energy supplied by the power supply is only the active power consumed in the circuit; The parallel resonance method is to use a reactor in parallel with the test sample to ensure that the circuit parameters meet the resonance requirements when the voltage of the test transformer meets the test requirements but the current does not. At this time, the inductive current of the reactor compensates for the capacitive current of the test sample.