E-field distribution analysis on three types of converter double valve in 800kV valve hall
Converter valve possesses the function of AC-DC voltage conversion and power transmission. It is an important device in the valve hall of UHVDC converter station. Since the corona discharge has a serious impact on the safe and stable operation of converter valve, it is necessary to analyze its surface electric field (E-field) distribution. In this paper, the structure characteristics of three typical double valve designs have been analyzed, which were respectively used in three high voltage (400-800kV) valve halls of one ±800kV UHVDC transmission project in China. Based on the project drawings, the equivalent model of each type of double valve with shielding structure was built with three-dimensional (3D) finite-element method (FEM) software ANSYS. Considering the interaction of double valves in actual valve hall, three double valve FEM models of same type in one hall, which formed the upper 6-pulse bridge in the 12-pulse converter unit, were built for the analysis of E-field distribution. Due to the hybrid AC-DC operating voltage, the transient E-field analysis with discrete loading voltage waveforms was adopted in these models. After calculation, the E-field distribution characteristic of different double valve types were summarized and compared under the normal operating condition. The results showed that the surface E-field strength on the shielding structure of all the double valves was lower than the critical value of corona inception and could meet the project requirements. This research could provide valuable references for shielding structure design and optimization of converter valve in the UHVDC transmission project.
Electromagnetic modelling of three phase UHVDC valve casing
Ultra High voltage DC transmission (UHVDC) is an efficient means of long distance power transmission, which has a voltage rating of + 800 kV. The major drawback of the HVDC system is electromagnetic interference produced by the conducting valves. Radiated EMI can be reduced by using shielding around the valve assembly. In this paper the three phase assembly of UHVDC converter valve is modeled in ANSYS. Effectiveness of shielding, firing sequence and overlapping on the electromagnetic field interference is analyzed. Aluminium shield with slit reduces the electromagnetic interference and it is well below the safe limit.
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