248 / 2018-09-24 20:30:40

Simulation and Optimization Design of Isolating Switch in the Indoor DC Yard of ±1100kV Converter Station

indoor DC yard,FEM,isolating switch,±1100kV UHVDC,optimization design

The Ultra High Voltage Direct Current (UHVDC) transmission technology, which is crucial to balance the reverse distribution pattern of energy and load center in China, has the advantages of large capacity, far distance, low energy consumption and so on. Currently, the Changji – Guquan ±1100kV UHVDC transmission project has already been built in China. And this project has by far the world's highest voltage level Direct Current (DC) transmission line.
As a key part of DC transmission project, Ultra High Voltage (UHV) converter station is mainly composed of converter valve unit, bushing, isolating switch and various supporting electric power fittings. Due to limited space of the indoor DC yard, air clearance between different devices is narrow. When the voltage level is raised to ± 1100kV, electric field distortion and corona discharge are prone to occur on surface of the fittings. Therefore, shape design of the grading and shielding fittings becomes an important issue.
Isolating switch in the indoor DC yard is vital to normal operation of the converter station. Because the isolating switch does not have the characteristics of arc quenching, electric field on the surface of the grading and shielding fittings may exceed the critical value or even produce corona discharge during operation if the performance of the fittings is not excellent enough, which will affect the normal operation of the converter station. Therefore, it is necessary to conduct a research on the distribution of electric field on the surface of the grading and shielding fittings and make reasonable optimization design for the fittings.
In this paper, by using Comsol as the software of finite element analysis, a three-dimensional model of the isolating switch was established, the simulation of the indoor DC yard was conducted and the distribution of electric field on the surface of the grading and shielding fittings was obtained.
It was found that when using 2400kV operating impulse test voltage as the boundary condition, electric field distortion on the surface of the double-ring-typed grading and shielding fittings appeared obviously and the highest electric field considerably exceeded the critical value. However, if the shield structure was modified to the mushroom-type, which meant using spherical or quasi-spherical shield device instead of double-ring-type, and all connected fittings and supports were covered inside the metal ball shell, the distribution of electric field would be greatly improved. In this case, the simulation results showed that the electric field on the surface of the fittings distributed more uniformly and the air clearance obviously increased. The grading and shielding effect of the mushroom-typed device was significantly better than that of the ordinary double-ring-typed device. Effects of the radius and the size of pore of the mushroom-typed grading and shielding fittings on the distribution of the electric field were studied by further adjustments and some correlation curves were obtained. Thus, some dimension parameters of the mushroom-typed grading and shielding fittings with better performance were given.
This result based on numerical calculation could provide theoretical basis for the optimization of different types of grading and shielding fittings on the isolating switch in UHV converter station. The mushroom-typed grading and shielding fittings could help improve the distribution of electric field and further to improve the operational security level of the whole substation.