Abstract
Corona discharge on the surface of power transmission and transformation fittings becomes increasingly serious with increasing voltage levels, especially for many grading rings in transformer substations. With the enhancement of people’s environmental awareness, the environmental protection administration requires noise and electromagnetic environment at transformer substations shall meet relevant standards. In order to suppress corona discharge on the surface of a grading ring, it is necessary to study its corona onset characteristics. Considering the basic physical process of the corona discharge, in this study, the electric field intensity is first calculated at any point in the space around the grading ring through ring charge simulation. Then, based on the theory of secondary electron emission, criteria for calculating the onset voltage of negative corona of the grading ring are derived, leading to an area factor of a photon absorption function suitable for the grading ring. In this way, a three-dimensional (3D) calculation physical model of the corona onset suitable for the grading ring is developed. This study calculates the corona onset voltage and field intensity of the grading ring under the typical working conditions by using the proposed 3D calculation physical model of the corona onset. The calculation results are compared with test results of the corona onset voltage and field intensity of grading rings in an outdoor 750 kV transformer substation in an ultrahigh voltage (UHV) alternating current (AC) test base. Furthermore, the simulation results of the area factor of the photon absorption function, electron collision coefficient, electron adsorption coefficient, and effective ionization coefficient in the 3D calculation physical model are obtained. In this way, the accuracy of the 3D calculation physical model of the corona onset proposed in this paper is verified. The research results can provide a theoretical basis for the corona prevention design of grading rings in extra high voltage/UHV AC power transmission and transformation projects.
Highlights
INTRODUCTIONFor this reason, when predicting the corona onset field intensity of electrodes with a large radius of curvature and non-cylindrical structure, the radius of curvature of the 2D structure in the formula fails to reflect 3D characteristics of electrode structures, incurring an obvious calculation error
As the voltage level rises, corona and electromagnetic environmental problems become increasingly prominent
The research results can provide a theoretical basis for the corona prevention design of grading rings in extra high voltage/ultrahigh voltage (UHV) alternating current (AC) power transmission and transformation projects
Summary
For this reason, when predicting the corona onset field intensity of electrodes with a large radius of curvature and non-cylindrical structure, the radius of curvature of the 2D structure in the formula fails to reflect 3D characteristics of electrode structures, incurring an obvious calculation error On this basis, some scholars have modified Peek’s formula using test data and obtained the theoretical limit of the corona onset field intensity suitable for grading rings.. Studies of corona characteristics of grading rings are rare: some scholars have deduced formulas for calculating the corona onset voltage and field intensity suitable for grading rings based on experimental and theoretical research; these formulas are not accurate enough to obtain universally applicable results. In order to establish the 3D calculation physical model of the corona onset and analyze the photon absorption function, the electron collision coefficient, the electron adsorption coefficient, and the effective ionization coefficient, the charge simulation method is proposed to calculate the electric field intensity. This paper studies the calculation method of 3D electric field intensity at any point around the grading ring based on ring charge simulation
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