Electric Field Analysis And Research On The Insulation Problems Of A Converter Transformer HVDC Bushing

In this paper, the purpose and significance of HVDC transmission was briefly discussed. The converter transformer is one of the key equipments, and the insulation and structure is the key technology and the main distinction between converter transformers and power transformers. Insulation fault is the highest while the products are tested and operated, and the fault of a converter transformer occurs in polarity reversal in most cases. HVDC bushing is not expensive itself, but its operation reliability and maintenance is very important to the normal operation of a converter transformer. So it is necessary for us to analyze the insulation problems of a converter transformer in the two aspects.On the basis of polarity reversal voltage theory analysis, in this paper, the distribution characteristics of end electrical field under different excitation and oil-paper compound insulation electric field of a converter transformer polarity reversal are analyzed. On the basis of which the electric field distribution characteristics of parallel-plate electric field and axisymmetrical electric field is discussed under polarity reversal voltage, a finite element method to calculate transient electric field is presented under polarity reversal voltage. The influence of medium resistivity and polarity reversal upon the internal insulation design is analyzed. The paper studies the relation of conductivity and field strength distribution and the relation of temperature and field strength distribution, and studies the influence of internal insulation structure and materials upon DC electric field distribution of external insulation.This paper puts emphasis on the research of the electric field calculation of HVDC bushing, which is used in DC transmission equipments and smoothing reactor, and the design of internal and external insulation structure, and discusses the influence of dielectric constant and polarity reversal and around insulation materials upon DC electric field distribution of internal insulation capacity core. Reviews the characteristics of HVDC bushing, and presents a method of computation of electric field and a design scheme of HVDC bushing. Emphatically studies the calculation of several key parameters of capacity core (such as each layer polar plate length, each layer polar plate radius and each layer polar plate insulation thickness, etc.), and develops the software of HVDC bushing capacity core design with FORTRAN, and discusses the cause of pollution flashover, the condition for pollution flashover and the harm of pollution flashover. Through the analysis to the external insulation flashover of HVDC bushing, presents concrete precautionary measures. Tentatively explores and studies the design of upper porcelain and lower porcelain which is used in the external insulation design of HVDC bushing.