Reliability evaluation of multiterminal HVDC systems has received very little attention in the past. This paper presents reliability modeling and analysis of an HVDC transmission system incorporating a voltage-sourced converter (VSC) tapping station. The use of VSC tapping stations enables the supply of power along the route to areas with comparatively little consumption. In this paper, a comprehensive detailed reliability model is developed and then converted to a manageable and computationally efficient model. Using this equivalent reliability model, various reliability indices are calculated at the load point of the system and the impacts of the VSC tapping station on these indices are illustrated. Sensitivity analyses are conducted to investigate the impacts of the load level and the location of the tapping station on the reliability indices. The conducted studies are numerically applied on a typical HVDC system and thorough discussions are presented.
Time-domain simulation (TDS) is the most accurate and reliable method for solving transient stability problem. This approach relies on the solution of nonlinear differential-algebraic equations (DAEs) using numerical integration, wherein a system of nonlinear equations is solved at each integration time step. Very DisHonest Newton (VDHN) method is one of the fastest available approaches for solving the system of nonlinear equations in the TDS. However, VDHN does not guarantee convergence and its sequential nature makes it difficult to take advantage of available multicore processors. This paper presents a new multi-decomposition approach (MDA) to achieve fast TDS, wherein the nonlinear system of DAEs is decomposed into three linear subsystems. An adaptive scheme is developed for updating the linear subsystems to ensure that approximation remains sufficiently accurate. The linear subsystems can be solved in parallel using multi-processor architecture. The MDA is demonstrated using IEEE 145-bus test system, and the results are verified against a commercial transient stability problem, Powertech Labs' DSATools.
The smart meters installed throughout the distribution networks in some regions have opened an opportunity to have reliable State Estimation (SE) at the distribution level. The reliable distribution system SE results can also be used to improve the accuracy and reliability of SE in transmission networks. This paper studies the impact of employing the results of distribution network SE as additional measurements in transmission network SE. It is shown that the observability of transmission networks can be restored using smart meters when it is unobservable.
Moreover, improvement in the robustness of SE in transmission networks is studied by monitoring the condition number of the gain matrix in the Weighted Least Squares (WLS) SE process. Finally, it is demonstrated that the accuracy of SE in transmission level can be improved using the results of SE on distribution level.Index Terms--Accuracy, distribution network state estimation, numerical stability, observability, smart grid, smart meters, transmission network state estimation.
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