DISEÑO DE SOPORTES AISLANTES EN TRANSFORMADORES SECOS EN MEDIA TENSIÓN

Abstract

Improvements on solid insulating materials over the last decades have allowed a fast progress in the medium voltage dry transformer technology compared to liquid-filled transformers. The design of air distances on dry type transformers presents a challenge; although they pass the routine dielectric tests, once in operation failures have been reported. Over-dimension of air distances has been adopted to avoid breakdown between upper high voltage side and the core frame thereby adding cost and size to the transformer. A critical part of the insulation system of these transformers is in the insulating supports used between windings and the clamping structure. This work proposes a design of these supports that can help to reduce their length without increasing the possibility of breakdown and decreasing the final cost of dry-type transformers. The tangential electric field in the support surface is calculated by means of the Finite Element Method (FEM) using a commercial software (COMSOL Multiphysics®), considering two and three dimensional configurations. The electric field distribution in the supports to reduce the tangential electric field using different profiles and different values of permittivity is investigated, considering some improvements in solid insulating materials. In this investigation, the electric field that represents the worst condition for the insulation structure of the transformer (Basic Insulation Level) is calculated, considering an electrostatic problem. Experimental tests were performed in order to verify the effect of the high operation temperature of dry type transformer on the breakdown voltage in the insulating supports. The experimental results are then used to define the design criteria used in the simulations. Te proposed designs are also tested in the high voltage laboratory of ESIME Zacatenco.