Cracking risk analysis and control for high‐voltage dry‐type valve‐side bushings

Abstract

The temperature gradient and mismatching between the thermal expansion of the core and flange readily lead to cracks and discharges on the core surface of the dry-type valve-side bushing, which severely impact the safety of power systems. It is vital to clarify the cracking risk of bushing cores under temperature gradients and establish corresponding control methods. The mechanical properties of epoxy resin impregnated paper (ERIP) material were measured in this study at different temperatures, and a thermal-mechanical coupling simulation model was established. The thermal and stress distributions of the core were obtained and the cracking risk was defined accordingly. The crack development mode was explored as it relates to the phase-field mode. Various elastic cushion materials affecting the stress distribution of the core were investigated. The results show that the mechanical properties of the ERIP material decrease rapidly as the temperature increases. When under severe working conditions, the maximum first principal stress of the core may be significantly higher than the tensile strength of the ERIP material resulting in significant axial cracks. Adding an elastic cushion layer made of polyurethane rubber can effectively relax the interface stress and reduce the cracking risk.

SF6 decomposition behaviour under partial discharge of typical insulation defects in gas‐solid insulated valve‐side bushing of converter transformer

“…As mentioned above, the bushing insulation is always subjected to a combination of DC and AC voltages during operation, which makes the electrical and thermal performance of ERIP-CTVSBs more demanding [14][15][16]. Unlike PDs inside GIS, PDs inside the ERIP-CTVSB occur not only in pure SF 6 gas, but more often on the surface of the gassolid insulation of SF 6 and ERIP, which may make the SF 6 decomposition behaviour inside the bushings different with that of GIS.…”

Degradation characteristics of insulation near aluminium foil edges inside dry‐type bushing cores under electrothermal compound stress

“…To qualitatively analyse the effect of temperature on each energy density type, an electric field strength of 8 kV⋅mm −1 and a frequency of 50 Hz are selected. Based on material parameters proposed by [8,21,22], the variation of each energy density with temperature in the material is obtained in Figure 23.…”

“…Even worse, with the increasing voltage level and transmission capacity of UHV DC projects, the thickness and length of the core insulation are significantly increased, making heat dissipation more difficult and the hot spot temperature much higher. Under such circumstances, the failure rate of the core insulation is higher under the action of electrothermal compound stress [8]. Notably, a bushing operated under high ambient temperature and current conditions may endure the above failures, and the breakdown point is usually located near the Al foil edge.…”

A zero‐sample state evaluation model for valve‐side bushing of UHV converter transformer oriented to digital twin under attribute analysis

“…The key to realizing the safe transmission of large capacity and long-distance power is to improve the operation and maintenance management level of power equipment. The valve-side bushing of the ultra-high voltage (UHV) converter transformer is the "bridge" and weak link to realize power conversion [2], and its running state stability directly affects the reliability of DC transmission projects. According to statistics, in recent years, power system failures caused by converter valve-side bushing of converter transformer account for 16.7% of all equipment failures [3], and the forms of failures also show diversity, such as SF6 gas leakage, aging of capacitor core, oil leakage, discharge, and so on [4][5][6][7].…”