Study On Return Voltage Measurement Of Oil-Paper Insulation Testing Technology In Transformers

Transformer is one of the most important equipment in the power system, assume the voltage conversion, distribution, transmission of electrical energy mandate in power network, which is an important prerequisite for safe and stable operation of power system safe and reliable operation. Once the transformer fault, it may lead to blackouts, and even the collapse of the power network, causing huge economic losses and serious social impact. A large number of studies have shown that the transformer fault mainly comes from the aging of the insulation. Therefore, the study transformers state detection method as well as the further study on its insulation testing system, testing and evaluation of transformer insulation aging state, is particularly important, and in accordance with the reasonable maintenance plan, the utilization of the transformer and the whole power system has important significance.Based on using the return voltage diagnosis of the transformer oil-paper insulation state on domestic and foreign, the transformer oil-paper insulation extended Debye model was established in this dissertation. Using the principle of circuit analysis derive mathematical expressions of the return voltage and polarization spectra which have one, two and n branches equivalent model. According to the data of dielectric polarization and depolarization currents obtained the return voltage by theoretical calculation. A numerical algorithm of the polarization and depolarization current to return voltage was proposed in this dissertation. At the same time, we used matlab to simulate the effectiveness of the method. And the matlab/simulink was used to build extended Debye model.Simultaneously, by analyzing the parameters such as charging voltage, charge and discharge time ratio and the law of different factors on the return voltage parameters change judge the overall state of the transformer insulation.A micro-current measurement circuit for polarization and depolarisation current(PDC) was designed and produced in this paper, the simulation analysis was carried out, and the methods of noise and interference suppression which obtained very good shielding effect were designed. The PDC experiment measure system is established in this paper, and the polarization-depolarization current of oil-paper insulation under different aging degrees were measured by the microcurrent measurement circuit, meanwhile, the experimentally measured polarization and depolarisation current numerical algorithm into return voltage. Related theoretical and experimental studies of polarization-depolarization current and return voltage in this thesis are valuable in theory and application.