Analytical methodology for reliability assessment of distribution networks with energy storage in islanded and emergency-tie restoration modes

A wide scale deployment of energy storage systems in power networks for energy balancing applications will lead to network reliability improvements. After a fault occurs in a network, energy storage will be able to help restore supply in the network areas isolated from the primary substation or in those re-connected to adjacent feeders of limited transfer capacity by emergency-ties. The reliability improvements introduced by energy storage need to be evaluated and quantified for both restoration modes. The objective of this paper is to assess the energy storage contribution in these restoration modes and to seek analytical, less computationally intensive solutions for such evaluation. The proposed analytical technique uses a probabilistic model of energy storage to assess the charge and discharge processes over a fault duration and the related operational strategy. In this way, reliability indices are calculated by taking into account the energy storage actions during a fault as well as the time-evolution of renewable generation and demand. These features lead to more realistic modelling of energy storage in analytical techniques. The proposed analytical technique was firstly validated by using a case study where the results obtained by Monte Carlo Simulation were used as a reference. Then, the proposed technique was applied to a distribution network to assess the reliability improvement provided by energy storage and to demonstrate the effectiveness and accuracy of the proposed approach.The authors kindly acknowledge the support of Fundacion Iberdrola to SinCortes project

Reliability assessment tools for future power distribution systems

Reliability of distribution networks is one of the fundamental parameters considered during power systems planning as it is used as a measure of continuity of supply delivered to consumers. Increased presence of renewable distributed generation, energy storage and other network management solutions is changing distribution systems by converting them to active distribution networks, as they have been commonly referred to in recent years. Operational properties of all these technological and management solutions can be harnessed to enhance the reliability of distribution networks. The objective of this thesis is to develop new analytical tools for the reliability assessment of active distribution networks including renewable distributed generation, energy storage, demand management and power-electronics devices. The proposed tools should allow an accurate and efficient evaluation of the previously mentioned technologies in reliability assessment studies. To achieve this objective, a detailed literature review in the field is performed first. The state-of-the-art with respect to the reliability assessment techniques is established and main research challenges identified. A novel analytical tool is proposed to assess the contribution of energy storage to reliability as the existing methodologies in this field lack accuracy or computational efficiency. By using the proposed tool, the computational times required for energy storage evaluation are significantly reduced and accurate results obtained. Then, a new methodology for the selection of adequate energy storage technology for reliability improvement applications is introduced. Based on the obtained reliability indices and cost-benefit results, recommendations for the technology and size of energy storage are provided demonstrating the applicability of the proposed methodology. In addition to energy storage, other network management solutions like dispatchable loads and power electronics devices are also modelled in reliability assessment. The optimal coordination of all these solutions is included in the evaluation, since this aspect has not been previously addressed by the existing tools. The obtained results indicate the network management solutions and their optimal coordination have a significant impact on reliability and, therefore, have to be taken into consideration during reliability assessment. The principal advantage of the developed tools is that they allow more accurate reliability evaluation of active distribution networks because the existing techniques and models cannot be used to assess these technologies and their operational properties. Moreover, the computational effciency of the tools allows a faster evaluation of different scenarios that are typically analysed during the planning stage. All these properties facilitate the task of network planners to design distribution networks with any preset reliability levels leading to decreased economic costs caused by power interruptions and reduced investments.La fiabilidad de las redes de distribución es un parámetro fundamental en la planificación de los sistemas eléctricos, ya que influye en el nivel de continuidad de suministro eléctrico de los consumidores. En la actualidad los sistemas de distribución eléctrica están experimentado un crecimiento sin precedentes en la penetración de generadores distribuidos de origen renovable, almacenamiento de energía y tecnología para la operación eficiente del sistema, dando lugar a redes de distribución activas. Todas estas tecnología pueden contribuir a mejorar la fiabilidad de las redes de distribución, siendo necesario evaluar su efecto. El objetivo de esta tesis consiste en desarrollar nuevas herramientas analíticas capaces de evaluar la fiabilidad de redes de distribución activas con generadores distribuidos renovables, almacenamiento de energía, gestión activa de la demanda y dispositivos de electrónica de potencia. Estas herramientas deben permitir una evaluación precisa y eficiente de dichas tecnologías en los estudios de fiabilidad. Para conseguir este objetivo, en primer lugar se lleva a cabo una revisión literaria de la temática, con el fin de determinar el estado del arte de las técnicas empleadas en la evaluación de la fiabilidad e identificar los principales retos de investigación. En segundo lugar, se propone una nueva herramienta para evaluar la contribución del almacenamiento de energía sobre la fiabilidad de las redes de distribución. Las metodologías existentes bien carecen de la precisión suficiente o bien necesitan de largos tiempos de computación, mientras que la herramienta propuesta permite reducir significativamente los tiempos de cálculo a la vez que proporcionada resultados precisos. Posteriormente, se presenta una metodología para seleccionar el sistema de almacenamiento más apropiado para mejorar la fiabilidad. Los resultados de fiabilidad y coste-beneficio proporcionados por dicha metodología permiten ayudar a seleccionar el tamaño y la tecnología de almacenamiento más apropiados. Además del almacenamiento de energía, se proponen nuevas herramientas para modelar soluciones empleadas en la gestión de redes activas, tales como cargas gestionables y dispositivos de electrónica de potencia. La coordinación óptima de todas estas soluciones es incluida en la evaluación de la fiabilidad, ya que dicho aspecto no ha sido evaluado por las herramientas existentes. Los resultados obtenidos ponen de manifiesto que las soluciones modeladas permiten mejorar significativamente la fiabilidad y, por ello, tienen que ser consideradas en los estudios de fiabilidad. La principal ventaja de las herramientas desarrolladas reside en que permiten una evaluación más precisa de la fiabilidad de redes activas de distribución. Además, permiten realizar una evaluación más rápida y, por consiguiente, analizar un mayor numero de escenarios en menos tiempo. Todas estas propiedades facilitan la tarea del planificador de red y le permiten diseñar redes activas de distribución con un nivel adecuado de fiabilidad, menores costes por interrupciones e inversiones más efectivas.I appreciate all the funding that have significantly contributed to the development of this research, specially to IMDEA Energy, Fundacion Iberdrola under SinCortes project, Spanish Ministry of Economy via RESmart project and Regional Community of Madrid with PRICAM projectPrograma de Doctorado en Ingeniería Eléctrica, Electrónica y Automática por la Universidad Carlos III de MadridPresidente: Stefania Conti.- Secretario: Julio Usaola García.- Vocal: José Jesús Fraile Ardanu

Evaluation of a quality improvement intervention to reduce anastomotic leak following right colectomy (EAGLE): pragmatic, batched stepped-wedge, cluster-randomized trial in 64 countries

Background Anastomotic leak affects 8 per cent of patients after right colectomy with a 10-fold increased risk of postoperative death. The EAGLE study aimed to develop and test whether an international, standardized quality improvement intervention could reduce anastomotic leaks. Methods The internationally intended protocol, iteratively co-developed by a multistage Delphi process, comprised an online educational module introducing risk stratification, an intraoperative checklist, and harmonized surgical techniques. Clusters (hospital teams) were randomized to one of three arms with varied sequences of intervention/data collection by a derived stepped-wedge batch design (at least 18 hospital teams per batch). Patients were blinded to the study allocation. Low- and middle-income country enrolment was encouraged. The primary outcome (assessed by intention to treat) was anastomotic leak rate, and subgroup analyses by module completion (at least 80 per cent of surgeons, high engagement; less than 50 per cent, low engagement) were preplanned. Results A total 355 hospital teams registered, with 332 from 64 countries (39.2 per cent low and middle income) included in the final analysis. The online modules were completed by half of the surgeons (2143 of 4411). The primary analysis included 3039 of the 3268 patients recruited (206 patients had no anastomosis and 23 were lost to follow-up), with anastomotic leaks arising before and after the intervention in 10.1 and 9.6 per cent respectively (adjusted OR 0.87, 95 per cent c.i. 0.59 to 1.30; P = 0.498). The proportion of surgeons completing the educational modules was an influence: the leak rate decreased from 12.2 per cent (61 of 500) before intervention to 5.1 per cent (24 of 473) after intervention in high-engagement centres (adjusted OR 0.36, 0.20 to 0.64; P < 0.001), but this was not observed in low-engagement hospitals (8.3 per cent (59 of 714) and 13.8 per cent (61 of 443) respectively; adjusted OR 2.09, 1.31 to 3.31). Conclusion Completion of globally available digital training by engaged teams can alter anastomotic leak rates. Registration number: NCT04270721 (http://www.clinicaltrials.gov)