Abstract
Ice covering on overhead transmission lines would cause damage to transmission system and long-term power outage. Among various de-icing devices, a modular multilevel converter based direct-current (DC)de-icer (MMC-DDI) is recognized as a promising solution due to its excellent technical performance. Its principle feasibility has been well studied, but only a small amount of literature discusses its economy or hardware optimization. To fill this gap, this paper presents a quantitative analysis and calculation on the converter characteristics of MMC-DDI. It reveals that, for a given DC de-icing requirement, the converter rating varies greatly with its alternating-current (AC) -side voltage, and it sometimes far exceeds the melting power. To reduce converter rating and improve its economy, an optimized configuration is proposed in which a proper transformer should be configured on the input AC-side of converter under certain conditions. This configuration is verified in an MMC-DDI for a 500 kV transmission line as a case study. The result shows, in the case of outputting the same de-icing characteristics, the optimized converter is reduced from 151 MVA to 68 MVA, and the total cost of the MMC-DDI system is reduced by 48%. This conclusion is conducive to the design optimization of multilevel DC de-icer and then to its engineering application.
Highlights
Ice covering on overhead transmission lines is a serious threat to the safe operation of power grids
Since this article focuses on the converter rating characteristics, the number of submodules in each arm was set as n = 4 to speed up the simulation
The simulation results of the dual-static var generators (SVGs), the conventional modular multilevel converter (MMC)-DC de-icer (DDI) and the optimized MMC-DDI are shown in Figures 5–7, respectively
Summary
Ice covering on overhead transmission lines is a serious threat to the safe operation of power grids. Among various de-icing methods, heating of ice-covered line conductors by electrical current is recognized as the most efficient engineering approach to minimize the catastrophic consequences of ice events [5,6,7,8] because it can eliminate the ice covered on hundreds of kilometers of line within an hour, without damaging the grid structure or polluting the environment. Both alternating-current (AC) and direct-current (DC) can be used to melt ice, but AC ice-melting is usually used for transmission lines up to 110 kV, while DC ice-melting is more recommended for high voltage lines up to 500 kV [3,4]
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