Charge Decay Characteristics On Barrier Surfaces Based On Barrier Effect

Raising the withstand performance of:air gaps is helpful to develop compact poxwer equipments,enhance the reliability of the equipments,and even to reduce the use of hexafluoride sulfur.Using barrier effect,which is introducing a barrier in the air gaps,can effectively increase the breakdown voltage.In this paper,a surface potential measurement platform was set up.The accumulations as well as decay of surface charges on the materials were experimentally investigated.The AC breakdown voltages and the surface charge characteristics of the barrier introduced in air gaps were also investigated to provide references for the development of the environment friendly gas insulated technology.Firstly,a surface potential measurement platform was set up.After analyzing the present methods of surface charge measurement,electrostatic probes were chosen for measuring the surface potential,according to the practical measurement needs.The surface potential measurement system was designed according to the principle of electrostatic probe method,including charging module,surface potential measurement module and motion-control module.The probe control and the data acquisition were realized through the upper computer written in LabVIEW virtual instrument.The steps of the experiment and the corresponding control codes were made and realized auto measurement eventually.Secondly,surface charge accumulation and decay characteristics of different materials were studied.The surface potential measurement platform was used to investigate the relationship between the surface potential distribution and charging time.Under a settled charging time,the surface potential distribution after different decay time and the relationship between surface potential and decay time were measured.The experimental results showed that under the same charging conditions,the initial value of different materials was different.The surface charges were mainly decay through the bulk of the material.The decay rates of different materials varied significantly and the material with a low initial surface potential decayed fast.Thirdly,the AC breakdown characteristics of the air gap with a barrier introduced and its relationship with barrier material parameters were investigated.The AC breakdown experiments were conducted with different barrier materials introduced at different positions.Mathematic models were used to deduce the parameters of the materials.The results showed that the material with the lowest initial surface potential and the fastest decay rate,due to the highest bulk conductivity and the lowest trap level,performed the highest increase on the AC breakdown voltages.This conclusion provides a reference for material selection.Finally,the surface charge characteristics of the barrier when used in the air-barrier insulation system were investigated.The positive and negative surface charge decay characteristics of the barrier when used in the insulation system were obtained by measuring the surface potential decay of the barrier when it is floated.The voltage polarity of breakdown was obtained by measuring the voltage wave.The breakdown paths were observed and compared with barrier surface residual charge distributions to find out the relationship of them.The experimental results show that the surface potential decay was slower when the barrier was floated.The voltage polarity of breakdown was positive.On the barrier,the paths where the electric arc went left more positive charges or neutralized the negative charges.