Study On Insulation Characteristics Of Converter Transformer Bushing Under The Temperature Gradient

Converter transformer bushing is one of key equipments in HVDC transmission system,used for electrical converter substations and converter between transformer and semiconductorvalve hall, transmission line connection, support and insulation to ground. Insulation failure isthe main cause of bushing failure of converter transformer in operation, this is because in thestrong electric field environment, it is easy to cause the change of rheological bushing localfield intensity is too high, resulting in an insulating medium and breakdown of insulationdamage. Therefore, the computation and analysis of the electric field intensity distribution ofthe converter transformer bushing in the different working conditions in operation, find out thehighest field strengths and bushing in the breakdown of insulation failure and root cause.This paper takes the600kV converter transformer bushing as research object, thedistribution of the electric field calculation of bushing in different types of test voltage stressusing finite element method, analysis of bushing insulation performance. First of all, withoutconsidering the temperature gradient under the influence of electric field in the AC, DC andpolarity reversal voltage excitation distribution bushing is calculated. The results show that:the converter transformer bushing under AC voltage electric field is capacitive distribution,and in the main insulation epoxy resin is concentrated in the DC voltage; under the action ofelectric field is resistance distribution, and in the SF6gas is concentrated; charge accumulationmedium under DC electric field will result in the distortion of bushing inner electric fieldpolarity reversal when the bushing pipe insulation, pose a great threat to.Under high voltage level converter transformer bushing, there will be another complexproblem, namely the bushing thermal insulation. This paper calculates the temperaturedistribution of bushing running stable for a long time at rated3600A current condition.Calculation of converter transformer bushing in the radial temperature gradient distribution onthe show from the inside to the outside to get low, intermediate and high; present at both endsof the trend in the axial direction, the maximum temperature appears at the top of theconductive rod near the epoxy resin. And when the insulation temperature rise, will seriouslyaffect the resistivity values, thus affecting the distribution of the electric field caused by theproblem of bushing, insulating. The temperature gradient changes the radial resistivity converter transformer bushing ofinsulating medium, so close to the external insulation at increasing electric field strength.According to the effects of temperature on the sleeve of the electric field intensity distribution,analysis of temperature gradient and sleeve DC polarity reversal electric field intensitydistribution calculation and. This converter transformer DC bushing development, hasimportant economic and social value as well as the development of HVDC technology. Theresults show that: the temperature gradient will cause the resistivity change and effect of theelectric field changes, resulting in insulation field distortion near the outer surface layer ofumbrella skirt. Therefore, the structural design of the umbrella skirt needs to be carefullyconsidered. And the temperature of the uneven will make the converter transformer bushinginternal local electric field intensity distortion, more easy to cause the destruction ofinsulation.