Study On The High-Field Conductance Mechanism And Space Charge Transport Of Polyethylene

Polyethylene materials are widely used in the field of electrical insulation because of their excellent mechanical and electrical properties.With the continuous improvement of UHV DC transmission levels,it puts forward higher requirements for the electrical resistance of polyethylene cable insulation material.At present,there are still many key scientific and technical problems to be solved urgently.First,the characteristic information of the conductance behavior of polyethylene cable insulation material at high electric field or even near breakdown,the transformation process of conductance mechanism,and the characteristics of space charge transport are still unclear.Secondly,the temperature of the cable will increase due to the loss of the core of the cable during operation,which makes the polyethylene cable insulation material work in a high temperature environment for a long time,and the high temperature and high field affect the space charge transport and conductivity of the polyethylene cable insulation material.Research has rarely been reported.In addition,in terms of analyzing the internal correlation between space charge and electrical conduction current,the measurement of space charge and electrical conduction current is mostly a step-by-step measurement,and the results obtained by measuring the same sample cannot be strictly analyzed systematically.Therefore,it is necessary to develop a joint measurement system that can measure space charge and high-field electric current at different temperatures at the same time and in situ,and use this as a basis to effectively develop the high electric field conductance mechanism and space of polyethylene cable insulation materials.The study of charge transport behavior and the exploration of more in-depth and comprehensive information about space charge transport behavior have important scientific significance and engineering application value for the development of the entire electrical insulation field.In this paper,the high field conductance behavior,threshold electric field change and space charge transport characteristics of polyethylene materials with electric field strength above 150 k V/mm are studied.The transition process of high field conductance mechanism of polyethylene materials is analyzed.The effects of electric field strength and temperature on space charge transport behavior of polyethylene high voltage cable insulation materials for industrial application are further studied,The transition process of the conductance mechanism was analyzed and the following work was completedA set of automatic high field conductance current measurement system with overload self-protection is developed.The system can measure electrical conduction current with an electric field strength of 200 k V/mm.Use this device to test low-density polyethylene(LDPE),medium-density polyethylene(MDPE),high-density polyethylene(HDPE)and linear low-density polyethylene(LLDPE)at room temperature.It is found that the threshold electric field from ohmic region to trap action region and from trap action region to trap filled region increase with the increase of polyethylene lamellar thickness,there is a transition from Poole-Frenkel bulk effect to Schottky electrode effect in the conductance mechanism.According to the basic principle of laser induced pressure pulse(LIPP)and the automatic high field conductance current measurement system,a joint measurement system for space charge and conductance current at different temperatures is developed.The space charge and conductance current of three kinds of insulating materials of high voltage cable which are made in China low density polyethylene,China crosslinked polyethylene and China diplomatic linked polyethylene were measured at different temperatures.The study found that: when the temperature constant,the three kinds of polyethylene material accumulation of the total charge of the overall increase with the increase of the electric field intensity,Among them,at the same electric field intensity,the domestic low density polyethylene accumulation of total charge rate than the other two material charge accumulation rate,China diplomatic linked polyethylene at low temperature accumulation rate of the total charge is lesser,but when the temperature rises to more than 50°C,the rate of total charge accumulation begins to increase,and the rate of domestic crosslinked polyethylene is the least.When the electric field intensity is constant,the total charge accumulated in the body of the three polyethylene materials increases with the increase of temperature.At the same temperature,the total charge accumulated in the domestic low density polyethylene is the largest,while the total charge accumulated in the Chinese foreign policy polyethylene is less when the electric field intensity is greater than 20 k V/mm.The rate of total charge accumulation is higher than that of the other two materials,and the amount of accumulated charge is relatively increased.The total charge accumulation of domestic crosslinked polyethylene is the least.It is also found that with the increase of electric field intensity,the conductance mechanism of the three kinds of polyethylene high-voltage cable insulation materials is gradually transformed from the Poole-Frenkel body effect to the Schottky electrode effect.