Experimental Study On High-field Conductivity Behavior Of Polyethylene Materials With Different Crystalline Characteristics

Polyethylene is a kind of thermoplastic resin obtained by polymerization of ethylene.Due to its own chemical structure,it is one of the most widely used insulating materials in the fields of high voltage transmission and electrical equipment.When a voltage is applied across the dielectric material,the electrical conductivity of the dielectric material increases,and space charge is likely to accumulate inside the polyethylene,causing electric field distortion.These factors will accelerate the degradation of insulation and greatly reduce its service life.With the development of high-voltage direct current transmission technology,the carrier transport mechanism inside the insulating medium under high-voltage strong fields has become more complicated,and at the same time,higher requirements are placed on the conductance current test equipment under high field strength,so it is necessary to insulate polyethylene Conduct in-depth research on the conductance behavior of materials in high fields and their test equipment and methods.This paper mainly discusses the realization of the conductance test of four different density polyethylene insulation materials under different electric field strengths and the test method under high field(near breakdown field strength),so as to further explore the high field conductivity of polyethylene Behavioral research provides basic conditions;The experiment qualitatively and quantitatively completed the crystallinity test of four different density polyethylenes through XRD and DSC test methods,the breakdown field strength test of polyethylene through electrical breakdown equipment,and the polymerization through the self-built high-field conductivity digital test system.Conductivity testing of ethylene;The study analyzed the influence of polyethylene density and crystallinity on the breakdown field strength of polyethylene and the possible reasons for the change of its conductance mechanism.It is found through experiments that four different density polyethylenes,such as low density polyethylene(LDPE),linear low density polyethylene(LLDPE),medium density polyethylene(MDPE),and high density polyethylene(HDPE),increase with density.Its crystallinity gradually increases;The breakdown field strength increases significantly with the increase of the crystallinity of polyethylene.The larger the shape parameter,the smaller the dispersion of the breakdown strength data,and the polyethylene shows more stable dielectric properties;In the test of the conductivity characteristics,the electric field threshold value of the transition from the ohmic region(T1 region)to the non-ohmic region of polyethylene gradually decreases,and the field strength corresponding to the turning point B of the non-ohmic region also gradually decreases;In the image under the lg I-lg E coordinate system,it is obtained by piecewise fitting: the slope of the conductivity characteristic curves of the four materials in the T1 area are very close to 1,which is almost the same as the theoretical value;The value range is 2?4,indicating that there is an SCLC effect in this area;the slope of the third curve(T3 area)is much lower than the slope of the T2 area curve;The conductivity mechanism of the four different density polyethylenes in the high field region has a transition process from the body(Poole-Frenkel)effect to the electrode(Schottky)effect.Strong threshold increases gradually.