Xinjiang electricity sending outside" project as national energy security protection and solution for "natural electricity shortage" problem of the eastern and the central region in future is constructing step by step. Sichuan power grid as an adjacent network of Xinjiang, due to its abundant hydropower resource, has already become one of the largest outside sending scale provincial power grid and existed a structural contradictory problem of "redundancy in wet season and shortage in dry season", which contributes to Sichuan power grid with both power given and relay out duality between supply and demand. As an effective way to solve the problem above, "Sending Xinjiang electricity to Sichuan power grid" project has been included in the plan and in implementation. However the outstanding problems of Sichuan power grid is in being a comparative high level of short-circuit current in present, in order to ensure security and stability of the grid in future, how to limit the short-circuit current level has been the key issue of all. The most of existing methods of short-circuit current limiting was relatively single and some of limitation effect was not satisfied. So it was lack of proper guidance especial for Sichuan power grid which has a more complicated transmission way and voltage grade. Therefore basing on a brief introduction of the short-circuit current damages and its limiting measures at home and abroad, simulations about short-circuit current of Sichuan power grid before and after ""Xinjiang electricity sending outside" project implementation and comparative analysis about the effect of each main single limiting method were carried out in this paper. Then an integrated current limiting scheme suitable for Sichuan power grid development was putted forward. And validation of the Manuscript
This paper presents an adaptive Under Frequency Load Shedding scheme based on Wide Area Measurement System. Due to the lack of enough adaptability to the operation state of the system, the traditional successive approximation under frequency load shedding method will cause excessive cut or undercut problems inevitably. This method consists first in a comprehensive weight index including load characteristics and inertias of generators. Then active-power deficit calculation based on the Low-order Frequency Response Model, concerning the effect of voltage was put forward. Finally, a dynamic correction of the load shedding amount was proposed to modify the scheme. This approach was applied to IEEE-39 system and the simulation results indicated that the proposed method was effective in reducing the load shedding amount as well as the frequency recovery time.
This paper analyzes the behaviour of a modular multilevel converter (MMC) based HVDC system under DC cable fault conditions. The behaviour of the HVDC system during a permanent line-to-line fault is analyzed in details at each stage of the fault timeline. Operation of the proposed system under a specific earthing configuration i.e. converter unearthed /AC transformer secondary side and DC cable solidly earthed, is also analyzed. Simulation studies are provided to assist the analytical analysis. It is observed that both faults leads to substantial AC and DC over-current and result in DC side oscillations
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