Design Of VLF Cosine Square Wave System And Discussion Of Dielectric Loss

Nowadays, many XLPE power cables are used for the project of city power grid renovation. Due to the extensive use of XLPE cable,It is related to the safe operation of the entire power system security. To ensure the safe and stable operation of XLPE cable, a variety of insulation tests are required.In addition to the withstand voltage test, but also for other non-destructive testing,die lectric loss measurement is one of the main items. The traditional withstand voltage tests have AC voltage test, DC voltage test and so on; but the traditional voltage test does not apply to the withstand voltage test of XLPE power cable. DC voltage will cause hidden damage to XLPE cable;AC voltage equipment has the shortcomings of heavy, bulky, inconvenient. In order to overcome the above problems, 0.1Hz ultra-low frequency voltage test technology is gradually on the rise. Because the ultra-low frequency system is small, light weight and withstand voltage test will not cause harm to XLPE cable,The test method is widely used. But ultra-low frequency cosine square wave voltage system can now only be uesd for the withstand voltage test, dielectric loss test method has not been relevant research based on withstand voltage systems of ultra-low-frequency cosine square wave.So this article will discuss the problem,providing a theoretical basis for future test of dielectric loss.Firstly, the development and application of 0.1Hz VLF cosine square wave voltage test are analyzed in this paper, next,this paper designs the VLF cosine square wave voltage test systems.Design of VLF cosine square wave voltage test system are as follows:the input of AC-rectifier filter circuit-inverter circuit-high-frequency transformer-doubler rectifier circuit-polarity switching circuit. This paper analyzes the main circuit topology calculates related parameters and optimizes the parameter of capacitor owned doubler rectifier circuit.The paper selected DSP chip as the main chip,By the voltage and current sampling of the the output of the circuit of doubler rectifier and polarity switching,forming PID closed-loop control system; PWM digital signal sent by the DSP is the control waveform of drive circuit.and compared to analog control of traditional scheme, this control method used by this paper is more flexible.In order to verify the correctness of the design,this paper build the 0.1Hz VLF cosine square-wave voltage system simulation model by Matlab/simulink simulation platform, proving the correctness of the design through the analysis of simulation results.The last chapter of this paper is theoretical analysis and calculations of tanδ test based on VLF cosine square-wave voltage system.Then we join simulation, exploring whether the calculation method is feasible by comparing simulation results and theoretical results. Lay the theoretical foundation for future testing of dielectric loss.