What is Grading Ring?

What is Grading Ring?

Compared to electric porcelain insulator, composite insulator is featured with high intensity, light weight, high wet-flashover and flashover voltage, easy operation maintenance, strong ability of impulse withstand, widely applied to transmission line suspension string, and has spread application in tension string in recent years. Surface field distribution and potential distribution for composite insulator without corona ring is greatly uneven, due to composite insulator structure characteristics and high resistivity feature of silicon rubber, surface field density is highest at mandrel and steel cap joint, distribution voltage is highest at first umbrella dress near high voltage end. Exorbitant surface field density not only generate corona discharge, affect transmission line electromagnetic environment, produce audible sound pollution, but also cause strong electric erosion, causing further insulator aging. Corona ring installation is the normal solution to the problem of uneven potential field density distribution at insulator high voltage end. Installation of corona ring helps to transfer maximum field density from insulator surface to corona ring surface, thus effectively improves electric field distribution on insulator surface.    
Optimal allocation for tension string and corona ring installed can be realized via on-site test study, yet with high cost and difficulty in operation, therefore finite element calculation is one economic and efficient way for electric field analysis. This essay establishes a simplified 3D model for ±800kV DC circuit including tower, divided conductor and tension string insulator based on finite element calculation, studies the rule of the influence of duplex insulator tension cascade interval on electric field distribution and on this basis studies influence caused by different corona ring parameters, thus finalize solution to corona ring distribution.


Grading Rings - checking welding

The solution to uneven potential field strength distribution at insulator high voltage end is normally installation of corona ring. After installing corona ring, maximum field strength transfer from insulator surface to corona ring surface, efficiently improve electric field distribution on insulator surface. Tension string and corona ring optimal configuration can be solved via on-site test study, yet with high test cost and difficult operation, therefore finite element calculation is an economic and efficient way to solve electric field distribution.

To provide rational grading ring configuration scheme for ± 800kV DC power line composite insulator tension string, this paper established 3D model for ± 800kV DC power line composite insulator tension string pole tower and split conductor, calculate electric field distribution for line-shaped tension string composite insulator, obtained optimal interval for line-shaped duplex tension string.

Research of influence of grading ring structure parameter on electric field distribution, obtain the outcome of optimized design. Application of designed grading ring structure, efficiently improved field strength distribution on insulator surface, limit insulator sheath, high voltage end hardware fittings and grading ring surface field strength within range of design.




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