Development Of AC Dielectric Performance Testing System For Polymer Semi-conductive Materials

Polymer semi-conductive material is a kind of filled conductive polymer,it's usually made of polymer insulation material and conductive materials by physical blending method.The composite material has both conductive ability and excellent mechanical properties.In the electrical field,the semi-conductive material is widely used in the insulation structure of cable and its accessories,which can play the role of uniform electric field.The dielectric properties of semi-conductive materials have a great influence on the reliability of insulation.The current evaluation index of electric power cable semi-conductive material is the DC volume resistivity,which is not applicable to the operation of the cable under the power frequency voltage for a long time,and the operating conditions of the high frequency voltage such as overvoltage and lightning overvoltage Therefore,it is necessary to study the dielectric properties of semi-conductive materials under different electric field frequency.The main purpose of this paper is to develop a set of AC dielectric properties test system for polymer semi-conductive materials to provide equipment support for the study of the AC dielectric properties.It is required that the measurement of AC equivalent resistivity,AC equivalent dielectric constant and loss factor can be achieved in the frequency range of 0 to 1MHz.According to the dielectric properties of semi-conducting materials,the equivalent circuit of resistance and capacitance parallel connection is established,which is used to characterize the conductance and polarization properties of materials.A test system based on three electrodes is designed.The sinusoidal voltage is used as the excitation signal.Due to the low resistivity of the semi-conductive materials,the driving shield consisting of the voltage follower is installed between the measuring pole and the protective pole to eliminate the leakage current of the protective pole.Synchronous excitation voltage and response time domain signal are calculated,and the equivalent dielectric parameters of AC are calculated by phase analysis.The testing system is based on virtual instrument technology,consisting of two parts: hardware and software.The hardware part mainly includes the computer,the lower computer,the DDS signal generator,the power amplifier,the electrode system,the measurement circuit and the data acquisition card.The software part is the test program developed by the LabVIEW software,including the serial communication,data collection,data processing,and the calculation of the dielectric parameters.The module was designed for each part of the testing system,and the physical circuit was made for test and evaluation.After ensuring the realization of the design goals of each module,a testing system was built.The accuracy of the testing system was checked by the parallel circuit of resistor and capacitor.The test results were compared with the results of the impedance analyzer,and the system check was completed.Under the three electrode system,the equivalent impedance of the measuring loop was measured and eliminated in the parameter calculation program,so as to reduce the test error.The samples were made by semi-conductive shielding material of electric power cable and tested.It was verified that the test system could test the AC dielectric properties of semi-conductive materials.