Research On The Distributed Electric Field Measurement Technology For The Electrical Tree In Insulation Material

Power transformer is the key equipment in power system.Most of the power transformers adopt oil-impregnated pressboard insulation system.The electrical tree inside the oil-impregnated pressboard is the important window of the insulation fault warning of power transformers.However,due to the opacity of pressboard,there has been a lack of effective means to observe the electrical trees generated inside the paperboard.At present,the distributed electric field measurement system proposed by the research group has realized the measurement of the electrical trees inside the cardboard,but its measurement accuracy needs to be improved.Therefore,it is very important for early warning of transformer insulation fault to explore the error reduction measures of measuring electrical trees by using distributed electric field measurement system.Firstly,based on the existing one-dimensional distributed electric field measurement system,an improved two-dimensional distributed electric field measurement system is proposed to reduce the error introduced by the distribution dimension of measurement electrode.In order to reduce the error introduced by the inverse problem algorithm,the existing inverse problem algorithm is improved.In addition,the error transfer law of inverse problem solving is studied in order to put forward the requirement of electric field measurement error.This paper mainly analyzes the electric field measurement error introduced by the capacitive voltage divider circuit and the distorted electric field of measuring electrode,and puts forward the corresponding error elimination methods.The preliminary results show that the distribution dimension of measurement electrodes increases,which can reduce the positioning error of the discharge points.The inverse problem algorithm used in this paper can greatly reduce the positioning error of discharge points,but it is sensitive to the electric field measurement error.It is necessary to take measures to restrain the error of electric field measurement.The measurement error of potential introduced by stray capacitance can be eliminated by calibration.The measurement error of potential introduced by stray capacitance of lead wire can be ignored.The potential measurement error caused by the equivalent capacitance cannot be eliminated directly,but the electric field ratio error caused by the equivalent capacitance can be eliminated by "Circle Drawing Points Selection Method".The proposed"Symmetric Points Selection Method" can simultaneously eliminate the errors caused by the equivalent capacitance Cx and the stray capacitance Ch of the high voltage electrode.The electric field measurement error is most significantly affected by the distance H from the measured electrode to the ground,while the influence of the diameter D and the distance S of the measuring electrodes is not significant.The electric field measurement error introduced by the distorted electric field of the measuring electrodes needs to be reduced by optimizing the parameters of the measuring electrodes.Finally,the electrode parameters were optimized and the optimal parameters of electrodes were obtained.Based on the optimal parameters of measuring electrodes and other error reduction measures,the positioning effect of discharge points in insulation is simulated and verified.The final research results of this paper show that the error reduction measures proposed in this paper can effectively reduce the positioning error of discharge points in insulation.