Development Of On-line Inspection System For Cable Insulation Based On Polarization And Depolarization Current

With the rapid development of China’s economy,the development of the electric-power industry is also gradually accelerating.Because of its excellent electrical and mechanical properties,power cables are widely used in distribution with network,industrial devices and other fields requiring large capacity of electricity,which is an important equipment for power transmission and distribution.Therefore,the healthy level of cable insulation is directly related to the life of thousands of households and the normal operation of various industrial and commercial places.The cable may be affected by the craft in the production process and insulation defects also may occur.It also may be affected by external heat,light and mechanical stress in the process of operation.They will make the original defects expand or add new defects,resulting in irreversible deterioration trend.Once the cable fails,it will cause inestimable loss to the society and economy.Most of the power cables being transported and laid in China are XLPE cables at present.The first XLPE cable came into service can be traced back to the 1970s.Many XLPE cables have been insulated because of their harsh environment or expiration date.Therefore,using an effective method to obtain the information of cable insulation condition in time and judge its insulation state is of great significance,and it is also an urgent problem to be solved in the current power industry.Based on the existing research at home and abroad,this thesis briefly analyzed the advantages and disadvantages of the existing on-line and off-line detection methods,emphatically introduced a new detection method based on dielectric response theory,and finally determines the design of cable on-line insulation diagnosis system using PDC method.PDC method is an on-line cable insulation diagnosis method based on medium response theory.Compared with traditional detection methods,it has the advantages of nondestructive testing,convenient operation and rich data acquisition.After calculated the relevant parameters,I established the model of high voltage cable extension Debye and distribution parameter.Then simulated experiments using these models These models were simulated using PDC method to simulate the effect of different insulation deterioration states on cables’ PDC.The accuracy of the PDC was verified by using recognized insulation state evaluation features such as insulation resistance,dielectric characteristics and partial discharge.Given the advantages of PDC method in XLPE cable insulation state diagnosis,this thesis developed a cable insulation on-line diagnosis system based on PDC method.The whole diagnosis system was divided into two parts,hardware and software.The hardware part mainly described the main control unit based on DSP,signal acquisition unit,dc high voltage unit,relay unit and Wi-Fi module several design ideas and methods.Tested the designed circuit board accordingly.The software part included the designing of upper computer program and hardware unit workflow.The man-machine interface and digital filter are designed using Lab VIEW software development platform.Finally,the designed cable insulation status online diagnosis system realized the polarization/depolarization test of the upper computer under the control of the upper computer,the test data can be sent back to the upper computer through the serial port to process,and the data can be received at the mobile phone end through the Wi-Fi module.Finally,the detection accuracy test and cable detection test were carried out for the designed detection system,which verified the validity and reliability of the detection system,obtained a large number of cable PDC data,enriched the data base of cable insulation on-line diagnosis system and reduced the possibility of safety accidents.