The Study Of Oil-paper Insulation Based On Polarization Depolarization Current Detection

Oil-paper insulation is widely used in voltage equipment dielectric material inthe power system, the insulation condition of oil-paper directly impact on theequipment safe. Moisture is one of the main factors affecting the performance of thepower transformer insulation, so, it is particularly important to study the moisture ofthe oil-paper insulation system. In recent decades, many scholars have developed anumber of oil-paper insulation methods, and summed up some new methods to judgeoil-paper insulation. Among them, the oil-immersed electrical equipment diagnosisbased on dielectric response theory gradually been paying attention. Oil-paperinsulation is a composite dielectric. As a non-destructive evaluation techniques，polarization and depolarization current method (PDC) has potential advantages andbroad application prospects in the dielectric properties of oil-paper insulation test.This paper analyzes the oil-paper electrical equipment micro-water sources,hazards, and research significance, and then, describes the dielectric response theory.In Matlab2010/simulink, establish the oil-paper insulation equivalent model based onDebye model and parameters comes from actual transformer model. Simulationanalysis the different circuit parameters influence on polarization and depolarizationcurrent. Build the test platform based on three electrodes in the laboratory; design thePDC test experiment and analysis the PDC test result. It is found that with increasinghumidity increases, the polarization and depolarization curves increases, and thegreater the humidity, the more obvious PDC curves uplift. Moisture reduces theinsulation resistance of the insulation system, increasing the capacitance, so that thecharge capacity of capacity enhancement.The paper proposed the polarization current maximum value, relatively stablevalue, the inject charge in polarization and inject charge in depolarization process asthe parameters to reflect the influence of humidity to the insulation performance ofsamples. In different humidity samples, the relevant parameters have some variation.Finally, we use two110kv current transformers (CT) to PDC test in lab, which comefrom one Power Company and produced in different years, and then analysis the testresults. In order to better illustrate the feasibility of PDC test methods, we measure thedielectric loss of the two CT. Comparing the two results, we found the dielectric losstest results and PDC test results have certain relevance.