Contingency ranking with respect to overloads in very large power systems taking into account uncertainty, preventive, and corrective actions

peer reviewedThis paper deals with day-ahead security management with respect to a postulated set of contingencies, while taking into account uncertainties about the next day generation/load scenario. In order to help the system operator in decision making under uncertainty, we aim at ranking these contingencies into four clusters according to the type of control actions needed to cover the worst uncertainty pattern of each contingency with respect to branch overload. To this end we use a fixed point algorithm that loops over two main modules: a discrete bi-level program (BLV) that computes the worst-case scenario, and a special kind of security constrained optimal power flow (SCOPF) which computes optimal preventive/corrective actions to cover the worst-case. We rely on a DC grid model, as the large number of binary variables, the large size of the problem, and the stringent computational requirements preclude the use of existing mixed integer nonlinear programming (MINLP) solvers. Consequently we solve the SCOPF using a mixed integer linear programming (MILP) solver while the BLV is decomposed into a series of MILPs. We provide numerical results with our approach on a very large European system model with 9241 buses and 5126 contingencies

Day-ahead Security Assessment under Uncertainty Relying on the Combination of Preventive and Corrective Controls to Face Worst-Case Scenarios

peer reviewedThis paper deals with day-ahead static security assessment with respect to a postulated set of contingencies while taking into account uncertainties about the next day system conditions. We propose a heuristic approach to check whether, given some assumptions regarding these uncertainties, the worst case with respect to each contingency is still controllable by appropriate combinations of preventive and corrective actions. This approach relies on the solution of successive optimal power flow (OPF) and security-constrained optimal power flow (SCOPF) problems of a special type. The interest of the approach is shown by illustrative examples on the Nordic32 system

Cautious operation planning under uncertainties

This paper deals with day-ahead power systems security planning under uncertainties, by posing an optimization problem over a set of power injection scenarios that could show up the next day and modeling the next day's real-time control strategies aiming at ensuring security with respect to contingencies by a combination of preventive and corrective controls. We seek to determine whether and which day-ahead decisions must be taken so that for scenarios over the next day there still exists an acceptable combination of preventive and corrective controls ensuring system security for any postulated contingency. We formulate this task as a three-stage feasibility checking problem, where the first stage corresponds to day-ahead decisions, the second stage to preventive control actions, and the third stage to corrective post-contingency controls. We propose a solution approach based on the problem decomposition into successive optimal power flow (OPF) and security-constrained optimal power flow (SCOPF) problems of a special type. Our approach is illustrated on the Nordic32 system and on a 1203-bus model of a real-life system

Local Mesh Refinement for Displacement-Based and Equilibrium-Based Finite Elements

International audienceIn this paper, a local mesh refinement algorithm for the computation of elastoplastic structures is presented. The elastoplastic computation is performed using a dual analysis combining two approaches: displacement-based and equilibrium-based finite elements. The remeshing scheme is applied to 3D structures discretized with three-dimensional tetrahedral meshes. Thanks to the dual approach, it is possible to assess a global error term that quantifies the distance between the displacement-based solution and the equilibrium solution. The local mesh refinement is based on the evaluation of the contribution of each element to this global error. This process is repeated as long as the distance between the two dual solutions doesn't respect an accepted tolerance. Themethod is illustrated on a real project steel assembly

Développement d'outils de calculs innovants dans l'ingénierie de génie civil

National audienceDesigning civil engineering structures has long involved the use of digital methods. Nevertheless, the way in which engineers apply said methods nowadays remains very limited and does not allow for a precise assessment of how a structure will behave in the event of failure. This results in a poor estimate of the safety margin available, often leading to oversizing of the structure. Recent developments in the construction world therefore raise questions about the need for more robust and relevant digital tools, in particular to meet environmental challenges. This article provides an overview of the use of these tools and explores recent developments in this area, made in collaboration between researchers and engineers.Le dimensionnement des ouvrages de génie civil repose, depuis longtemps, sur l'utilisation de méthodes numériques. Néanmoins, la pratique qu'en font actuellement les ingénieurs reste encore très limitée et ne permet pas d'évaluer précisément le comportement des ouvrages à la ruine. Il en résulte une mauvaise estimation de la marge de sécurité disponible, conduisant bien souvent au surdimensionnement de l'ouvrage. Les évolutions récentes que connaît le secteur de la construction questionnent donc le besoin d'outils numériques plus robustes et plus pertinents, notamment, pour répondre au défi écologique. Cet article dresse un panorama de cet usage et met en lumière les outils récents développés grâce à une collaboration entre le monde académique et celui de l'ingénierie

Externally prestressed concrete: anchor block 3D yield design

International audienceIn externally prestressed structures, anchors and deviators are used to connect tendons to the main structure. Those reinforced concrete blocks are exposed to large stress concentration and in many cases need 3D non-linear computation to be assessed properly, especially when they are beyond the standard framework. This local stress computation remains a great challenge for externally prestressed bridge design or large span girders design and is often poorly evaluated. This paper presents the results of a nonlinear 3D analysis of an anchor block belonging to an 80 meters long externally prestressed box girder. This analysis has been done for an actual engineering study (Roissy Charles de Gaulle Airport, Paris) to understand the concrete stress behaviour and cracking causes at the anchorage zone. Each reinforcing bar is modelled, plain concrete is described by the Rankine criterion, and finite elements are 10-nodes tetrahedrons. Then, a yield design computation is performed to assess the safety factor on the ultimate state loading. For the collapse load, an elastoplastic analysis is computed thanks to a static approach and a kinematic approach. This dual approach gives an error estimation in constitutive law. Eventually, stress flaws and rebars constrains are analysed in order to understand the general behaviour of the anchor. © 2022 IABSE Symposium Prague, 2022: Challenges for Existing and Oncoming Structures - Report. All rights reserved

Externally prestressed concrete: anchor block 3D yield design

International audienceIn externally prestressed structures, anchors and deviators are used to connect tendons to the main structure. Those reinforced concrete blocks are exposed to large stress concentration and in many cases need 3D non-linear computation to be assessed properly, especially when they are beyond the standard framework. This local stress computation remains a great challenge for externally prestressed bridge design or large span girders design and is often poorly evaluated. This paper presents the results of a nonlinear 3D analysis of an anchor block belonging to an 80 meters long externally prestressed box girder. This analysis has been done for an actual engineering study (Roissy Charles de Gaulle Airport, Paris) to understand the concrete stress behaviour and cracking causes at the anchorage zone. Each reinforcing bar is modelled, plain concrete is described by the Rankine criterion, and finite elements are 10-nodes tetrahedrons. Then, a yield design computation is performed to assess the safety factor on the ultimate state loading. For the collapse load, an elastoplastic analysis is computed thanks to a static approach and a kinematic approach. This dual approach gives an error estimation in constitutive law. Eventually, stress flaws and rebars constrains are analysed in order to understand the general behaviour of the anchor. © 2022 IABSE Symposium Prague, 2022: Challenges for Existing and Oncoming Structures - Report. All rights reserved