Research On Insulation Fault Detection Technology For Bushing Used In Valve-side Of Converter Transformer

Bushing used in Valve-side of Converter Transformer is an important power equipment,its insulation performance is related of bushing and converter transformer's safety and reliability.Dry SF₆ gas insulated DC bushing is more and more used in converter transformer because of its excellent electrical performance.However,the research on its insulation detection technology is few.Because of this,in this paper,the insulation characteristic of the dry SF₆ gas insulated DC bushing is studied,and the defect of the capacitor screen,the metal particle defect and the moisture defect are set up,and the normal capacitor core is prepared.The contents and achievements of this paper are as follows:The dielectric loss factor and the capacitance of the core of the bushing model are measured under high frequency and low frequency voltage.Under the high voltage of 50 Hz,the dielectric loss factor of the damped defect is the highest,the other core is lower,and the metal particle defect core capacity is the smallest.From the results of frequency domain dielectric spectroscopy,the capacitance and dielectric loss factor of the different defective bushing capacitance core increases with the decrease of the frequency,but the amplitude of the two parameters in different defective bushing capacitance core are different.The difference of capacitance of the four capacitor model decreases with the decrease of the applied power frequency,and the difference of dielectric loss factor increases with the decrease of the applied power frequency.The partial discharge characteristics of the core of the bushing were measured under DC voltage.The discharge capacity and the number of discharges varied greatly with the defects of the capacitor core.The discharge capacity increased first and then decreased with the increase of the discharge capacity,and reached the maximum at 35 pC.The core discharges of capacitive screen gap are concentrated below 30 pC,and the distribution is relatively uniform.Discharge of moisture defects capacitor core discharges are concentrated below 25 pC and discharge times are high.By comparing the skewness,the steepness,and the local peak number,the difference between the defective casing and the defective casing can be determined.The decomposition products of SF₆ gas under partial discharge were tested.SOF₂?SO₂F₂?SO₂ were the highest rate at the beginning of the test,and SO₂ gas production rate was higher than that of CF₄ in the case of metal particle defects and moisture imperfections in the SF₆ gas decomposition products detection test,and the defect of the capacitor screen exactly the opposite.The ratios of SOF₂/ SO₂F₂?CF₄/ SO₂??SOF₂+ SO₂F₂?/?CF₄+ SO₂?were chosen as characteristic values to characterize the different defects.Three defective component ratios were calculated.The ratio of the characteristic components of different defects is different,and it is feasible to use the ratio as the characteristic quantity to characterize the defect type.In this paper,the insulation characteristics of the dry SF₆ gas insulated DC bushing are exploratory studied,the results and conclusions provides an important support for the actual bushing insulation detection,with a certain reference value.