The Influence of Temperature on Draw Rod System of Converter Transformer Grid Side Bushing

At present, a typical type oil-paper insulation bushing with draw rod system is widely used as grid side bushing of UHV converter transformer in China. The current carrying and mechanical compensation structure of this special draw rod system is complex, and its internal pulling force and expansion size are affected by environmental temperature, structural size, elastic modulus, expansion coefficient and other factors, which leads to several draw rod system failures. It is urgent to accurately evaluate and verify the influence of draw rod system on the performance of that typical type bushing. Firstly, the calculation model of the draw rod system of the typical type grid side bushing is established. Then, the influence of temperature on the top size expansion and the pressure of the current carrying contact surface in draw rod system are measured, through sensors of temperature, pressure and displacement which are placed on actual gird side bushing. Finally, the calculated results should be compared with the experimental results. It is indicated that these two results are close to each other. The pulling force of the draw rod system increase with the increase of environmental temperature, and the axial load on the bottom contact increases, which accelerates the failure of screw connection. At last, serious discharge fault occurs due to the falling off of bottom contact. The failure mechanism of the current carrying structure at the bottom of the draw rod system under high ambient temperature is analyzed in this paper. The provided results can be a foundation to improve the reliability of the draw rod system of that typical type gird side bushing, as well as condition assessment and quality inspection methods.