Research On Charged Detection System Of Oil-immersed Current Transformer Insulation Defects

Oil-immersed CT is indispensable equipment in the power system,easy to produce insulation,causes partial discharge and arc discharge,even explode.Study reliable method suitable for oil-immersed CT charged detection,dectct oil-immersed CT accident timely,so as to improve the safety and reliability of power grid application,and apply in practice has great significance.Oil-immersed CT’s heat-resisting performance is poorer,this can lead to aging and inflammable shortcomings,This can increase the hidden danger of oil leakage.Although the tachonology of oil-immersed CT had great progress,solved the problems such as leakage,but due to the actual situation of CT,its insulation pofermance is still unreliable,easy to produce inslation defects,cause partial discharge and arc discharge,and then cause explosion.In the past,the detection methods of oil-immersed CT are traditional,the insulation defects are detected after the equipment malfunction,unable to timely anticipate the running state of the device.This article studies oil-immersed CT charged detection technology based on the principle of pulse current method.Oil-immersed CT’s insulation detects mainly emerge in the form of partial discharge pulse current.Partial discharge happens with the neutralization of positive and negative charges,produce a steep pulse curret,so we can measure the pulse current at the earth point or neutral point of power equipment through Rogowisk coil,or using measuring impedance to acquire the discharge information at coupling capacitance.The method by using pulse curret to detect the pulse current in end screen called "end screen" method,it’s a widely used test method at present.Based on pulse current method,this article proposed the "primary side difference method","primary side difference method" can effectively improve the accuracy of the data in the application charged detection of oi-immersed CT insulation.This article first summarizes four typical insulation defects of oil-immersed CT: primary side guide rod metal protrusions discharge,capacitive screen broken,insulating paper loose fault,end screen imperfect earth.Emphatically introduce the design principle and use method of the charged detection system based on "primary side difference method",focus on the building experimental platform,conduct safety research under high voltage,response research under large current and research of resistance to electromagnetic interference.Finally,compare with traditinal "end screen" method,separstely use two test motheds to detect four typically insulation defects of oil-immersed CT,draw the corresponding N-φ-Q figure,discharge ellipse figure and pulse V-φ figure.Experimental results show that primary side difference method can accurately dectect primary side guide rod metal protrusions discharge,capacitive screen broken,insulating paper loose fault and end screen imperfect earth detects.For air gap discharge,primary side difference method has better detection effect and higher accuracy than end scrren method.