Many years of operation experience at home and abroad shows that DC voltage withstand test is not suitable for rubber plastic power cable in handover or preventive test, and AC voltage withstand test (frequency range 30-300hz) should be used to ensure the safe movement of cable. This is an epoch-making change in the development history of preventive test of power equipment.

However, DC voltage withstand test is still effective for oil immersed paper insulated power cables, and should be continued to be used. It is not suitable to use large capacity power frequency test transformer on site because of the large capacity of the cable. The frequency modulation series resonance high voltage test equipment has the advantages of light weight, small power supply

capacity (only 1/ 30~ 1 / 80 of the power supply capacity of the test transformer), good voltage waveform, easy to handle and suitable for field use.

This test equipment is specially designed and manufactured for field AC withstand voltage test of rubber and plastic power cable, and is applicable to handover test and preventive test. The main components of the whole set of equipment include: frequency conversion control box, resonance reactor, excitation transformer, capacitor voltage divider, etc.

The working principle wiring of frequency modulation series resonance high voltage test equipment is shown in Figure 1. The 380V/ 50Hz AC power supply outputs a 30-300hz frequency adjustable voltage through the frequency converter, which is sent to the excitation transformer to boost to 0-2000v, and forms a high-voltage main harmonic circuit through the resonance reactor L (the resonance reactor can be used in series or in parallel depending on the tested cable and voltage level and length) and the tested cable Cx. The capacitor voltage divider is pure capacitance type, which is used to measure the test voltage.

Firstly, the frequency converter sends a lower voltage ue to the main resonance circuit through the excitation transformer T, and adjusts the output frequency of the frequency converter. When the frequency reaches the resonance frequency, the output frequency of the frequency converter is adjusted.