Abstract
Vertical load is the power flow between electrical transmission and distribution networks. In the past, large-scale generators connected to transmission systems supplied consumers connected to lower voltage levels across distribution grids. Thus, vertical loads tended to be downward-oriented. This paper presents a spatiotemporal distributed energy resources (DER) diffusion model to analyze vertical load uncertainty resulting from different DER diffusion process representations currently used in the industry and academia. Network planners and operators can use such model to understand the long-term evolution of load at the T/D boundary. The proposal is applied to the Portuguese power system, combining, as first of its kind, highly granulated population census with georeferenced transmission and distribution network datasets. This application analyzes the 20-year evolution of such vertical load flows at the transmission-distribution boundary under a strong uptake of DER embodied in lower voltage levels in Portugal. © 2019 IEEE.

Abstract
The continuous shift from TSO connected generation to DSO connection generation is presenting new challenges to DSOs and TSOs. Keeping the system up and running in the future requires a more collaborative approach to the issue of DSO/TSO cooperation that has existed so far in the vertically integrated network paradigm. It is possible to use IT tools to make sure both system operators have the relevant information they require to fulfil their mission.TDX-Assist’s Portuguese demo helps addressing these issues by:focusing on the provision of reactive power services by the DSO to the TSO. A new version of the Interval Constrained Power Flow (ICPF) tool, which takes into account disjoint flexibility areas as a result of the combination of discrete control variables, will be used to evaluate the range of operation points at the primary substations (Figure 1). With this information, the TSO can then select an operation point that will cause minimum impact on the transmission network.designing and implementing the information exchange needed to support other dimensions such as operational planning through nodal forecast at nodal level and exchange of maintenance plans in a defined observability area of both system operators

Abstract
The increasing penetration of renewable energy sources characterized by a high degree of variability and uncertainty is a complex challenge for network operators that are obligated to ensure their connection while keeping the quality and security of supply. In order to deal with this variable behavior and forecast uncertainty, the distribution networks are equipped with flexible distributed energy resources capable of adjusting their operating point to avoid technical issues (voltage problems, congestion, etc.). Within this paradigm, the flexibility that, in fact, can be provided by such resources, needs to be estimated/forecasted up to the transmission network node (primary substation) and requires new tools for TSO/DSO coordination. This paper addresses this topic by developing a methodology capable of finding the flexibility area while taking into account the technical grid constraints. The proposed approach is based on the formulation of a single optimization problem which is run several times, according with the expected precision for the flexibility area estimation. To each optimization problem run, a different objective function belonging to a family of straight lines is assigned. This allows exploring the active and reactive power flow limits at the TSO/DSO boundary nodes - which define the flexibility area. The effectiveness of the proposed model has been evaluated on two test networks and the results suggest a step forward in the TSO/DSO coordination field. Nevertheless, further investigations to study the effect of assets with discrete control nature (e.g., on load tap changers - OLTC, capacitor banks) on the occurrence of disjoint flexibility areas should be carried. © 2017 Elsevier Ltd.

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