Research On The Measurement Of Electric Field In Oil Of Oil-paper Insulation Under Impulse Voltage

The power transformer is the core of the power system,and its insulation design is the most important.The electric field distribution of oil-paper insulation structure under impact voltage is a key tache in the design of transformer insulation.If we can accurately measure the electric field and its change characteristics with the temperature and moisture in the transformer oil-paper insulating oil under impulse voltage.For improving its insulation design,promote transformer insulation strength and power grid over-voltage level has great significance.The impulse voltage is a unipolar pulse voltage,which is easy to produce a large amount of space charge.At present,most of the transformer impulse electric field calculations are based on the capacitive field equivalent of the simulation software,can not consider the impact of space charge on the electric field.We can only according to the theoretical calculation results combined with the allowable field strength to select a reasonable margin as the design value.However,the simulation results are lack of support and verification of the actual measurement,the electric field characteristic under the impulse voltage is not clear.In view of the current impulse voltage in oil of oil-paper insulation in the measurement of electric field measurement sensitivity and accuracy of the problem is still low,this paper based on the principle of Kerr effect,presents a non-contact measurement method for the electric field distribution of oil-paper insulation under impulse voltage.A set of optical system,photoelectric conversion device,organic glass sealing cell,impulse voltage source,temperature and water cycle control system composed of oil paper insulation electric field measurement device was developed,which laid the foundation for the measurement of the electric field in oil of oil-paper insulation.In order to solve the problem of accuracy of electric field measurement,this paper analyzed influences from the aspects of the objective factors,The influence include inherent noise,temperature,electric field calculation method,additional phase difference and angle adjustment accuracy and the corresponding methods to eliminate the influence of the larger sources of error is presented.The performance of the device was calibrated and tested under the uniform electric field using a brass plate electrode.The results show that the measured value of the electric field at low voltage is in good agreement with the actual value of the electric field,The peak value of 3.49 k V / mm lightning impact electric field,the maximum error of only 3.56%,solve the measurement sensitivity and low accuracy of the problem.The influence of temperature and moisture on the electric field in oil under the action of impulse voltage is studied by using the developed measuring device.The results show that under 60 k V standard lightning impulse voltage,the electric field in the oil decreases with the increase of temperature,in 60?,the peak amplitude of the largest is 9.2%,and in 60?,the peak amplitude decreased 41.6%;At 100 k V standard lightning impulse voltage,when the moisture content is low,the electric field in the oil is little different from the applied electric field.With the increase of the moisture content in the oil,the electric field in the oil shows a decreasing trend,the maximum drop rate reached 20.5%.The qualitative analysis of test results are as follows: with the rise of temperature or moisture in oil,oil resistivity decreased according to the reference data and the existing available,the oil from the anode plate emitted positive ion migration rate,in a very short of the time across the electric field measurement points,thereby weakening the space electric field;because water is a strong polar molecule,polarization effect is obvious,with the increase of moisture in oil,the number of water molecules per unit volume increased,the polarization effect of external applied electric field weakening is more and more obvious.