Analysis of electrical–thermal‐stress characteristics for eccentric contact strip in the valve‐side bushing of converter transformer

Abstract

Ultra‐high voltage direct current (UHVDC) transmission project in China is expanding, and the technology is increasingly maturing. The converter transformer is a crucial component in the UHVDC transmission projects, and its valve‐side bushing plays a key role in ensuring the stable operation of the power system. This paper investigates the electrical–thermal‐stress distribution characteristics of the contact strip in an eccentric state. The research focuses on a section of the contact strip in the plug oil at the tail end of the bushing on the valve side of the converter. A three‐dimensional finite element simulation model is established, and the contact strip contact resistance is used to define the contact strip eccentricity. The temperature rise platform of the contact strip was constructed to verify the precision of the simulation outcomes. The study investigated the variations in electric, thermal, and stress of contact strips in various eccentric states, as well as transient development, and the four stages of contact strip deformation were summarised using calculation results, providing quantitative analysis criteria for assessing the degree of deterioration of contact strips under eccentric conditions. Through the test and calculation, it can be seen that the contact resistance of the normal contact strip changes with the height in the form of a typical first‐order exponential function. The contact resistance value is between 200 and 400 μΩ under the actual mounting height; for the brand‐new contact strip, the maximum temperature difference is 2.984 K without other interference; and after 15 min, the maximum displacements of the upper and lower half‐ring strips reached are 84.3 and 83.7 μm, respectively, due to the thermal expansion. The study results offer a theoretical foundation for understanding the failure of elastic electrical connection components in the bushing on the valve side of the converter.