Electric Field Analysis Of±1000kV DC Wall Bushing

UHV (Ultra-high voltage) DC (direct current) wall bushing is an import ant equipment of UHV DC transmission system. It plays a key role in the economic transfer, flexible allocation and safe usage of power. However, the UHV DC wall bushing is a double-edged sword. Because if the insulation is damaged, the bushing not only has no protective effect, but also may cau se damage to other equipments and the surrounding electric power operation. At present our country has the technical strength to make rectification trans formers and other high-end equipments already, but±800kV DC wall bushin gs, higher voltage (such as±1000kV and±1100kV) DC wall bushings and o ther high-end equipments still rely on foreign imports mostly. The reason is that there are a lot of difficult to solve the insulation problems such as pa rtial discharge, dielectric properties and heat-resistant properties of these UH V DC high-end equipments, which makes the insulation design and optimiza tion of the UHV DC wall bushing a difficult problem.One of the problems of researching the UHV DC wall bushing is the s pace charge effects. The+1000kV DC wall bushing under planning bears n ot only the normal DC and AC operating voltage, but also the polarity reve rsal impulse voltage which appears in the process of phase commutation. Sp ace charge always exists widely under various work conditions. The existen ce, transfer, and even disappearance of space charge would distort the electri c field distribution inside the insulating medium, and thus the material can be damaged in early stage and finally breakdown. In DC electric field, espe cially during polarity reversal, the accumulation of space charges will distort electric field distribution in polymer seriously, and thus threaten the safe o peration of UHV DC wall bushing. Therefore, it is necessary to research the electric field distribution and space charge effects of the UHV DC wall bu shing in a strong electric field condition.To find a useful solution to resolve the problems of insulation, not onl y new insulation materials should be researched and developed, but also the electric field analysis of the bushing, and further insulation construction opt imization are necessary. In this paper, the electric field distribution of±100OkV DC wall bushing is analyzed by using the finite element software. First ly, a finite element model for±1000kV DC wall bushing is established by the commercial software ElecNet, to analyze the electric field distribution un der DC, AC and polarity reversal conditions especially considering the space charge effects. The change of the electric field distribution under different working conditions is explained with the theory of space charge. Secondly, t he electric field distribution with thermal stress is also calculated in this pap er to incorporate the influence of the dielectric temperature gradients. Beside s, the software simulation of electric field distribution and the measured ther mal field distribution are combined in this paper to propose an indirect met hod of measuring the electric field distribution. Finally, based on the electric field analysis of±1000kV DC wall bushing, the methods of improving th e electric field distribution and insulation construction optimization are explo red. The structural analysis and size optimization of the capacitor core, gradi ng ring, inner electrode and stress cone of the bushing are respectively rese arched. The research results provide useful reference for further design and development of UHV DC wall bushings.In this paper, the electric field distribution under different conditions wi th considering the space charge effects, and the insulation construction optim ization of±1000kV DC wall bushing are analyzed. The research has import ant applications, economic value and social benefits for the design and devel opment of UHV DC high-end equipments, and the development of UHV D C transmission technology.