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.
Electric-field Simulation of Insulation Type Test of ±420kV HVDC Flexible Converter Valve
In order to observe the electric-field distribution of insulation type test of ±420 kV flexible converter valve. This work builds the 3D model of ±420 kV flexible converter valve tower, Ansoft is used to simulate the electrostatic field. Results show that: when the flexible converter valve is doing a high voltage test, the negative potential in suspension conductors will be generated, the potential distribution degree are various, this phenomenon may be caused by the density difference of electric charges which are induced by different potential between left and right valve components; Results of electric-field simulation for each component suggest that, electric-field concentration likes to appear in the corner of shield and grading ring, and the tip position on capacitor metal component etc., the corner of 1th and 5th layer shields have the maximum electric-field $2 \times10 ^{\mathbf{6}}$V/m, this value is $\lt 3$ kV/mm, as for the valve components, the electric-field of 1th $\sim4$ th layers’ valve component are higher than that of the 5th layer’s valve component, the reason may be that: because the 5th layer’s valve component has a large distance from the top plane(0V), the electric-field lines distribution is sparse, so the electric-field is low; the electric-field value of insulators such as supporting insulators are 105 V/m order of magnitudes, this is lower compared to the breakdown threshold $2 \times10 ^{\mathbf{7}}$ V/m of insulator materials itself.
Effects of reservoir volume on performance of pulse tube cooler.
A pulse tube cooler has the advantages of long-life and low-vibration over conventional cryocoolers such as G-M and Stirling coolers because of the absence of moving parts at low temperature. On the other hand, the combination of a reservoir and orifice is indispensable to optimize the performance of pulse tube coolers. In order to make the pulse tube cooler compact for practical applications, the volume of reservoir should be minimized. This paper analyzes the effects of the reservoir volume on the thermodynamic performance of various components in a simple orifice and a double-inlet pulse tube cooler by combining a linearized model with a thermodynamic analysis. Expressions of entropy production for those components are presented. The results show that the reservoir volume has a significant influence on the entropy production in the various components when the reservoir to pulse tube volume ratio is smaller than about 5. The ratio is important to determine the minimum reservoir volume for a pulse tube cooler. Optimum settings for a double-inlet pulse tube cooler are also discussed.