Structure Optimization of UHV RIP Oil-SF6 bushings Based on Improved Equal Margin Design Method and Back-Propagation Neural Network

Zhang Shiling

doi:10.1051/e3sconf/202126103040

Abstract

Equal margin design method based on the classic analytic formula is widely used in development of extra-high voltage bushing products, and its effectiveness and practicality have been fully validated. However, model and temperature factors have significant impact on internal E-field distribution of UHVAC and UHVDC bushing condenser, which traditional analytic formula is difficult to evaluate quantitatively, so it’s necessary to improve traditional equal margin design method. Firstly, basic principles of equal margin design method and its software package were briefly described, and the laws of model and temperature factors influencing on condenser E-field were investigated on FEM (finite element method) computing platform. Based on these, mathematical model of improved equal margin design method for bushing condenser was established, and flow chart of optimization process combining FEM electro-thermal coupling calculation with genetic algorithm was presented. The improved method was applied to design of UHV RIP oil-gas prototype to realize uniform axial E-field distribution along bushing condenser and equal partial discharge margin between adjacent foils. Bushing condenser was fabricated according to above optimized design structure, and has passed all type tests. In the paper, the FEM electro-thermal coupling calculation method was applied to the inner insulation optimization design to make bushing condenser’s design more suitable. The paper can provide some theoretical guidelines for research and development of other bushings in UHV level.

Highlights

Capacitive bushing is a common type of bushing in UHV/UHV power system at present: a capacitor core is added between the central guide rod and the flange as the internal insulation, and there are multi-layer metal plates in the capacitor core to control the electric field uniformity inside and on the surface of the bushing
The results show that the radial electric field distribution of the bushing core presents U-shaped distribution of high at both ends and low in the middle, and the maximum electric field strength of the center guide rod side is higher than that of the flange side
An improved design method of the equal margin for internal insulation of high-voltage capacitive bushing is realized by combining electrothermal coupling calculation and genetic algorithm in finite element calculation environment, and a prototype of UHV oil and gas bushing is successfully developed by using this method: 1) Considering the structure and isothermal condition of the bushing capacitance core, the electric field distribution inside the core calculated by the traditional design software package is consistent with that calculated by the finite element method, which proves the effectiveness of the finite element method in calculating the electric field distribution inside the bushing core

Summary

Introduction

Capacitive bushing is a common type of bushing in UHV/UHV power system at present: a capacitor core is added between the central guide rod and the flange as the internal insulation, and there are multi-layer metal plates in the capacitor core to control the electric field uniformity inside and on the surface of the bushing. In reference[2], the equal margin method is developed as software package for the optimal design of capacitor core of high voltage capacitive bushing. If the number of internal layers n, the distribution of axial electric field Ea and the overall size of the core remain unchanged, and the insulation thickness between the layers is properly adjusted, the inter layer margin Ui / U can be equal. At this time, the initial partial discharge voltage of bushing is:. The ratio of the initial partial discharge voltage of each insulation layer to the voltage distributed on the layer should be equal to a constant: Uik U k

AErk K

Conclusion