| Ethylene-propylene rubber(EPR)is widely used as power cable of coal mine for its excellent oxidation resistance and corrosion resistance.However,the operating environment of mine cable is very serious.Under the action of external squeezing,friction or pulling mechanical stress,the insulation of cable is easily damaged.In addition,cable joints and terminals are the weakest links in underground coal mines.This is because during the high humidity environment,the infiltration of fluid spread along the damaged part of the cable or the loosely sealed part of the joint.The fluid will evaporate due to the high temperature,forming a cavity between the insulation and the shield of the cable or the cable joint.Under the action of electric field,there will be an uneven distribution of electric field in these parts,and discharge will be formed at the interface between air and EPR insulation,which will lead to cable insulation failure in the long term.Therefore,it is of great significance to study the discharge characteristics of EPR insulation material along the surface for understanding the deterioration of cable insulation or the development of fault law.Aiming at the problem of EPR cable electrical discharge on the surface of insulation layer,this paper takes EPR as study object.The surface discharge characteristics at different temperature and electric field distribution,the effect of surface fluorination modification on the electrical resistance of EPR rubber surface are studied in this paper.The surface potential decay characteristics of EPR and the method of surface discharge pattern recognition are studied in detail.The research contents are as follows: The temperature and electric field distribution is the main factors affecting the rubber surface discharge and insulation deterioration.This paper firstly builds surface discharge test platform under various temperature ranges which were from 30 °C to 120 °C.Under the process of flashover,the surface discharge spectrum was plotted and the surface discharge characteristics were extracted.Temperature and electric field distribution are the main influencing factors of EPR surface discharge and insulation deterioration.In this paper,a variable-temperature test platform is set up to simulate the process of surface discharge to flashover at ambient temperature of 30 °C,60 °C,90 °C and 120 °C,respectively.In order to study the effect of electric field distribution on the discharge along the surface,the surface discharge spectrum at different temperatures was measured.The cylindrical electrode,needle plate electrode and coaxial cylindrical electrode model were selected to simulate the slightly uneven electric field at room temperature,respectively,to study the effect of electric field distribution on the discharge along the surface.The discharge to flashover process in the extreme non-uniform electric field and the uniform electric field distribution is studied.The ?-q spectrum of the discharge along the surface is measured by the discharge pulse measurement system.The characteristics of the discharge along the surface under the different electric field distribution are analyzed.The influence mechanism of electric field distribution on surface discharge is revealed.It is found that the surface discharge characteristic quantity of EPR rubber is different under different temperature and electric field distribution,according to the change trend of discharge characteristic quantity.The process of flashover can be divided into four stages: the initial stage of discharge,the stage of discharge development,the phase of discharge phase holding and the stage of approaching flashover.Surface fluorination is a method of surface modification of polymer materials,which is used to improve the mechanical and electrical properties of the surface of the materials.Surface fluorination is used to modify the surface of ethylene-propylene rubber(EPR).Firstly,the dielectric properties and microstructure of the modified EPR were tested,and it was found that the dielectric constant of the modified EPR was obviously changed.The surface morphology became compact.The electrical indentation properties of ethylene-propylene rubber treated with different fluorination time were tested.The results of standard electric mark test showed that the surface electrical scar area and corrosion loss of ethylene-propylene rubber were decreased after fluorination.The results show that fluorination can improve the electrical indentation resistance of EPR surface,and that the sample with 240 min fluorination time has the smallest electric mark area and corrosion loss,which indicates that the optimum fluorination time can improve the etch resistance of ethylene-propylene-propylene rubber surface to the greatest extent.Surface charge accumulation is one of the main reasons for the local electric field concentration on the EPR insulation surface.In this paper,a measuring platform for the dynamic distribution of EPR surface potential has been built,and different polarities have been measured.The effect of corona of amplitude and time on the surface potential attenuation characteristics of EPR was studied.The energy level density distribution of EPR surface trap was calculated,and the surface charge transfer and internal carrier transport mechanism of EPR were analyzed.Main conclusions are included: the effect of different corona charging time on the surface potential decay of EPR shows that the decay rate of EPR surface potential decreases with the increase of corona time,which is due to the increase of corona time.The number of surface trapping carriers increases and the probability of detrapping decreases after the carriers are trapped,thus forming the phenomenon of surface charge accumulation.In this paper,the sparse decomposition is used as the main method to identify the surface discharge of EPR under different situation.The discharge repetition,average and maximum discharge magnitude as a function of discharge phase is investigated under electric field distribution of slightly non-uniform(90°C and 30 °C),highly non-uniform(30 °C)and uniform(30 °C),respectively.The discharge repetition,average and maximum discharge magnitude are extracted to construct the feature value.Then the eigenvector based on the characteristic parameters is established.The surface discharge training atom library is constructed from all characteristic eigenvector.The relationship between temperature and EPR insulation surface discharge is studied. |
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