Effect of long‐term fluorination on surface electrical performance of ethylene propylene rubber

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Effect of thermal ageing on space charge in ethylene propylene rubber at DC voltage

To understand the space charge characteristics of ethylene propylene rubber (EPR) used in MV/HV power cables under thermal stress, the space charge profile is measured by the pulsed electro-acoustic method under 20 kV/mm at 120 and 160 \ub0C. The complex permittivity and physicochemical properties at the different ageing stages are measured and analyzed for an understanding of the effects of thermal ageing on space charge characteristics. The trap properties of EPR during thermal ageing is calculated and analyzed based on the space charge decay model. The results show that both the ageing time and temperature can affect the space charge characteristics of EPR The space charge characteristics of EPR can be ascribed to the trapping sites caused by the complex chemical and physical structures during thermal ageing. Under the thermal oxygen process, the polar groups and ions increase because of the EPR molecular chain breakages, and the charge injection from the electrodes increases. Based on the decay model of space charge and isothermal decay current theory, the distribution of trap levels in EPR at different ageing stages is obtained. The trap distribution under different ageing process can be explained by the theory of trap filling

Study on evaluation method of insulation performance of mine cable based on dielectric response method

The high voltage cable used in mine is affected by many factors, such as electricity, heat and machinery stress. These factors accelerate insulation aging and easily lead to cable leakage, short circuit or discharge. At present, the dielectric response method is introduced into analysis, evaluation and diagnosis of insulation performance and aging state of mine cables. In view of problems of insulation performance and aging state evaluation of mine cables, the commonly used ethylene propylene diene monomer (EPDM) insulated mobile flexible cable for mining is taken as the research object. The basic principles and typical characteristics of recovery voltage method, polarization/depolarization current method and frequency-domain dielectric spectroscopy method in dielectric response method are summarized. The advantages and disadvantages of the three methods are compared. The characteristics of cable insulation performance evaluation based on the dielectric response model are introduced. The characteristics include the aging factor extracted by the extended Debye model, relaxation characteristics extracted by the modified dielectric relaxation model and dielectric loss integral spectrum. The application of the dielectric response method in the evaluation of the insulation performance of mine cables is summarized from the following aspects. The aspects include the identification of trace corrosion degree of mine cables based on recovery voltage method and polarization/depolarization current method. The aspects include the evaluation of EPDM insulation multi-stress aging state based on polarization/depolarization current method and isothermal relaxation current, based on dielectric relaxation model and based on dielectric loss integral value. The existing online monitoring technology for the evaluation of the insulation performance of mine cables based on the dielectric response method cannot adapt to the working conditions of coal mines. The evaluation data is insufficient, and the relationship between the insulation deterioration degree and the characteristic quantity is unknown. In order to solve the above problems, this paper puts forward that the research should focus on two key technologies, namely, cable insulation state perception and the relationship between insulation degradation degree and characteristic quantity construction