Design And Research Of The Variable-Frequency Series-Resonant Voltage Withstand Testing System

With the rapid development of the power industry in China and with more and more XLPE cables being installed and used, the conduction of on-site ac withstand voltage test is a necessity in order to guarantee the quality of XLPE cables before installation. Because of its unique superiorities, the method of variable-frequency series-resonant voltage withstand test has been widely used currently and will still be the forefront of research in this area in the future. This paper studies the core content of the variable-frequency series-resonant voltage withstand test of XLPE cables which entails the following parts:Firstly, makes the conclusion:the variable-frequency series-resonant voltage withstand test is the best method for on-site ac withstand voltage test after comparison with several widely used ac withstand voltage test method. Also, this paper studies and designs the structure and main circuit of the core part in the withstand voltage test—the variable frequency power supply. This incorporates the design of the general structure of the variable frequency power supply and the research on the full-bridge Inverter circuit. It masters the method for the SPWM technique frequency and voltage control, defined bipolar through analysis of the actual parameters of the inverter circuit and realized SPWM by asynchronous modulation.Incorporating the calculation and selection of the high voltage DC modules, this paper chooses the IPM and the connection of main circuit according to the specific parameter of the variable frequency power supply being designed.When it comes to the design of the wave filter of the variable frequency power supply, this paper initially adopted the traditional LC wave filter. However, after analysis of the impact of the no-load disturbance harmonic oscillation, this paper designs the split capacitor method LC wave filter after verification its validity through simulation and harmonic wave analysis of the no-load output wave.Lastly this paper designs the general structure of the variable-frequency series-resonant voltage withstand test system. It selects the parameter of the main circuit of the voltage withstand test system after calculation and research on the resonant frequency, loop current and cable test voltage. This paper:1) draws the conclusion that the testing system of the main circuit is feasible after simulation analysis of the cable voltage withstand test.;2) conducts the tuning analysis of the voltage withstand system;3) calculates the range of the tuning of cables with different capacitance by way of tuning in small range of frequency to perform the XLPE cable’s voltage withstand test;4) elaborates the way to determine the resonance. It selects the maximum value of the capacitance cable being tested as the resonance of the circuit and confirms the evidence and process of the determination. And finally, it verified the validity and feasibility by simulation analysis.