Research On The Measurements Of Electric Field Distribution And Space Charge In Liquid Dielectrics Under Pulse Voltage Based On Kerr Effect

The electric breakdown characteristic of insulation materials is a key factoraffecting the development of electrical equipment and power industry， the insulationproperties of the dielectric are greatly influenced by the internal electric field， and theexistence of space charge plays an important role in changing the electric fielddistribution of insulation dielectric. Therefore， it has important theoreticalsignificances and engineering application values to establish a kind of measuring systemand get a novel measurement technique of space charge in liquid dielectric， to researchthe tendency of both electric field and space charge in insulation materials.On the basis of reading and analysis of massive literatures， aiming at the highdisturbance， slow rate of data acquisition and shortage of dynamic measurement innow surface charge measuring system，this paper has established a new high-speedmeasuring system of space charge based on the Kerr electro-optic effect. Depending onthe combination of existing mature photoelectric detection system，we have verified theelectric field measurement of this established system and determine the Kerr coefficientof the propylene carbonate liquid used in this experiment. The result shows that the Kerrcoefficient B of propylene carbonate is1.22×10^-12m/V². According to the basic principlesand natures of Jones matrix，we figure out the transmission matrix of this space chargemeasuring system as wave plates’ number and optical axis angle change. Besides，therelationship between light intensity ratio and phase under different conditions could also bedetermined. When two wave plates were added to the measuring system，we find that theisoclines of electro-optic field figure will disappear. Combined with the image processingtechnique，the method of determining the maximum number of interference fringes will provide asolid theoretical foundation for the calculation of the electric field and space charge in theelectro-optic field figure.By using the new space charge measuring system，this paper has studied the electro-optic fieldfigure between two parallel plates when electrode materials and polarity of the applied voltagechange. The results shows the polarity of space charges injected into the liquid will be differentunder different combinations of electrode materials. Positive charges will be injected when theelectrode is made of aluminum while stainless steel electrode will inject negative charges intothe liquid. However，positive charges will also be injected under several circumstances if this twoelectrodes’ material is not the same. Positive charges and negative charges were both found injected for brass electrode. Under circumstance of the same electrode material，thepolarity of injected charges will also changes due to the different polarity of the appliedpulse voltage. The influence of space charge is one of the important reasons for differentphenomenon，it changes the surface composition of the electrode and affect the parallelplate electrodes’ space charges emission ability. Therefore，considering different polarity ofthe applied voltage，the dielectric strength of liquid dielectrics will be improved byselecting appropriate combination of electrode materials. And in this paper,nondestructive measurements of the electric field between two Paralleled electrodes in theinsulating dielectric liquid that is added with nanomaterial are carried out for the first time byusing the space charge measuring system. The results shows that the electric field and itsdistortion between two Paralleled electrodes are both small after adding nanomaterial tothe test sample, which effectively producing the breakdown voltage in the insulatingdielectric under negative voltage.