Electric Field Distribution and Switching Impulse Discharge under Shield Ball Surface Scratch Defect in an UHVDC Hall

Jianghai Geng,Xiuyuan Yao,Fangcheng Lv,Yuchen Qin,Yujian Ding

doi:10.3390/en11061408

Jianghai Geng, Xiuyuan Yao + Show 3 more

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https://doi.org/10.3390/en11061408

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Journal: Energies	Publication Date: May 31, 2018
Citations: 8	License type: CC BY 4.0

Affiliation: North China Electric Power University

Abstract

The dimension and surface state of shielding fittings in ultra high voltage direct current (UHVDC) converter station valve halls have a great influence on their surface electric field and switching impulse characteristics, which are important parameters confirming the air gap distance in the valve hall. The characteristics of impulse discharge under different lengths, dent degrees and burrs around the scratches of Φ1.3 m shield balls with a 2 m sphere-plane gap length were tested, in the UHVDC testing base of the Hebei Electric Power Research Institute. The discharge characteristics under the influence of the surface scratches of the shield ball were obtained. The results demonstrate that the discharge voltage of sphere-plane gap decreases obviously when there are unpolished scratches on the surface of the shield ball. However, when the scratches are polished, the discharge voltage has no significant impact. At the same time, a 1:1 full-scale impulse test model was established based on the finite element method. The electric field intensity and the space electric field distribution of the shield ball were obtained under the influence of scratches with or without burrs. The results of the simulation show that when the surface of the shield ball is smooth, the electric field distribution around it is even. The electric field intensity on the surface of the shield ball increases obviously when there are burrs around the scratches. When there is no burr around the scratches, the length and depth of the scratches have no obvious effect on its electric field distribution. Meanwhile, calculation results are consistent with test results. The results can provide an important basis for the design and optimization of shielding fittings, and technical support for its localization.

Highlights

Valve halls of direct current (DC) converter stations are the most important links in ultra-high-voltage (UHV) DC transmission projects and are responsible for the vital task of DC/AC conversion
BurrsThrough around the scratchescalculations, will greatly when the scratches are surrounded by burrs, the maximum surface electric field intensity greater increase the surface electric field intensity of the shield ball
The aim of this research was to explore the influences of the scratch on the discharge characteristics of the long sphere-plane air gap under switching impulses of positive polarity

Summary

Introduction

Valve halls of direct current (DC) converter stations are the most important links in ultra-high-voltage (UHV) DC transmission projects and are responsible for the vital task of DC/AC (alternating current) conversion. Various items of high-voltage equipment are installed in a valve hall, in which the equipment and circuits have complex structures and different equipment presents large voltage differences. For this reason, the electrical clearance around equipment in valve halls, and the safety margin of the electric field intensity need to be strictly controlled, so as to avoid the occurrence of corona [1,2,3,4]. High-voltage equipment in the valve hall of a converter station are electrically connected by linking the fittings therein whose structural dimensions directly influence the distribution of electric field intensity in the whole valve hall. The air gaps in a valve hall are generally sphere-plane and sphere-sphere types, which form a non-uniform

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