Electric Field Distribution And Research On The Insulation Properties About Valve Side Bushing Of Converter Transformer

Converter transformer and valve side of converter transformer bushing are the AC and DC transmission systems’ core devices of converter and inverter interfaces at both ends. Since there is a common effect of AC and DC electric field, so they requested that its high reliability and high performance. With HVDC increased transmission capacity and enhance the voltage level, compared to other converter station primary devices, DC casing is more prone to failure, this put forward higher requirements for DC casing manufacturing level and operational reliability. During the runtime of the valve side of the converter transformer bushing, space charge where Insulated equipment accumulate distortion of the electric field nearly. it makes the casing electric field’s distribution inside the local area focus, and it is prone to flashover or disruptive discharge, than it lead to the destruction of the main insulation sleeve, when severe, he will burn in fire, There may be other insulating device detonated around even more damage occurs, so that the whole system down, resulting in power outages. When the casing to withstand AC voltage, DC voltage, AC and DC voltage and voltage polarity reversal, space charge will have a complex effect on the internal electric field, and this produce a serious threat to the safe operation of the entire HVDC transmission system. In summary, this article has important practical significance to space charge impact the electric field at different conditions of HVDC bushings.This paper describes the electrical properties and the critical of high-voltage bushing, it also describes the breakdown characteristics of high voltage bushings. Than this paper research the bushing design of inner and outer insulation. Clarify the importance of internal and external insulation After clarifying the theory of internal and external insulation coordination. the paper proposed the key factor what affect the UHVDC bushing electric field.The paper builds a finite element model of UHVDC bushings. By comparing the commonly used numerical methods casing electric field, it conduct the method called finite element method. The paper introduces the INFOLYTICA finite element analysis software and establishes a computational model of the charge distribution around the casing.The paper does a simulation experiment and it considers the impact of space charge exchanges steady exchanges and transient electric field, the experiment also considers the influence of the space charge current steady state electric field and transient electric field. The result proves that in the DC voltage, the space charge will have a huge impact to casing field. And in the condition of frequency AC voltage, the influence of the space charge electric field on the casing is mainly reflected in the transient and it has little effect, and it almost no effect on the steady-state field under normal operating conditions. The paper studies the influence of the space charge to HVDC bushing field when it is in the field of polarity reversal. While the end moment of polarity reversal electric, the field strength reaches a maximum polarity and it is the maximum of the whole process in SF6 side of the plate. Kerr effect is made to measurements the casing electric field, by comparing the test results and simulation results obtained it is feasible of this method.