MONITORING OF CAPACITOR-TYPE BUSHINGS CONSIDERATIONS REGARDING THE INFLUENCE OF THERMAL FIELD DISTRIBUTION ON DIELECTRIC LOSSES

摘要

The paper presents a study of the temperature field, using the finite element method, for a 123 kV 1600 A isolated outdoor bushing, immersed in warm oil. The operation condition is a stationary one, corresponding to an operation extreme from the point of view of the thermal load. For carrying out this study, the 3D modelling of the above mentioned bushing was performed. The insulating fitting of the bushing is made of 20 layers of bakelite paper. The stationary condition determines, in the annular slit made between the inner surface of the aluminium pipe and the outer surface of the copper terminal, the heating of transformer oil up to a maximum temperature T = 90°C. The bushing contains also capacitor oil, inside other annular slit made between the outer surface of the capacitor and the inner surface of the ceramic insulator. The analysis study is done taking into account the extreme thermal stresses, focusing at the level of the first cooling wing section of the ceramic insulator. This fact enables to justify the tan5 variation in time, depending on the transformer loading and the environmental conditions.