Research On Cable Dielectric Loss Factor Detection System Based On Sweep Method

The development of social economy and the pace of modernization are becoming more rapidly. As the connection of electrical equipment and transmission, the use of cables is in-creasing. The insulation of cables will directly affect the safe operation of the whole power system. As a kind of non-destructive detection method, dielectric loss factor detection has important guiding significance for the electrical equipment’s insulation state evaluation. In order to ensure electrical equipment can operate safely and reliably, dielectric loss factor detection should be regularly taken. The current domestic dielectric loss factor detectors use a single frequency. It’s hard to avoid the interference problems during the process of measure-ment. The foreign similar products have adopted the sweep method to test the dielectric loss factor, but they’re quite expensive. According to the background, this paper proposes a cable dielectric loss factor detection system based on the sweep method.The detection system is composed of four parts:sweep generator module, voltage amp-lification module, data acquisition module and digital signal processing module.(1) The traditional LC frequency control method and phase lock loop technology are narrated in the paper. The methods have some disadvantages on accuracy and controllabi-lity.On the contrary, the direct digital synthesis method has advantages on sweep signal gene-ration. Its working principle and control method are deeply discussed.(2) The high voltage op-amp PA340is chosen as the main voltage amplification chip. The dc power supply circuit, compensation capacitance circuit, protection circuit are designed in the paper. The stable output waveforms show that the system can drive the capacitive load and meet the design requirements.(3) The voltage and current signal need to be processed, and then sent to the AD conversion chip AD7714. Single chip microcomputer and AD7714interface circuit, power circuit, input and output circuits are designed in the paper.(4) The digital methods for the measurement including zero-crossing method, DFT method and correlation analysis method are discussed in detail. According to the Matlab simulation, DFT method adding windows is used to be the final digital signal processing method. Finally it gives the cable detection data and compares with the same kind of domestic instrument.The results prove that the detection system is accurate, stable and has great practical value.