Investigation into the protection of microgrids using adaptive relays

Due to a proliferation of renewable power sources and a rise in distributed generators, the transmission network is now able to split into smaller isolated sections. These sections are often referred to as microgrids as they function similar to larger networks with power production being sufficient to power the loads. Microgrids are hampered by the lack of fault current being sufficiently high to operate traditional overcurrent protection. The lack of fault current has resulted in a need to find newer methods to provide fault protection. One such method is the use of modern relays that allow for the trip settings to be changed as the network itself changes. Relays that allow for this adaption are known as adaptive relays and provide a method to deal with the lower fault current when the microgrid is isolated from the main network by reducing their pickup current as appropriate. The effectiveness of adaptive relays has been investigated by the use of DIgSILENT PowerFactory simulation software to model two differing networks under varying conditions. The networks chosen to be simulated, consist of a test network used in previous research and a modelling of a physical network on Hailuoto Island. The networks were simulated with the faults falling into one of the following four categories: 1. Faults occurring on the external grid 2. Faults occurring on the feeder connecting the external grid to the microgrid 3. Faults occurring on the feeders inside the microgrid 4. Faults occurring on the loads and connections inside the microgrid The adaptive relays were found to operate correctly having discrimination between relays, once the pickup currents were calculated correctly. Each microgrid requires that a microprocessor, being informed of the status of the grid and output of each power source, calculate the pickup currents for each relay, and notify the relay of its new pickup current. The microprocessor’s calculations were simulated in MathWorks MATLAB via a script which allows calculation of the current seen by a relay as the sum of the rated output from each distributed generator. Then multiplied by the status of the generator and its percentage contribution. This formula is an adaption from previous work by (Oudalov and Fidigatti n.d.). The current calculated by the MATLAB script is found when compared to the PowerFactory simulations as having a difference of less than 2.8 per cent and 8 per cent on the test network and Hailuoto Island respectively. Providing proof that not only does the MATLAB script and its associated formula work, so do adaptive relays for protecting microgrids

Islanding detection during intended island operation of nested microgrid

In the future, functionalities like islanding detection must also operate during intended island operation of (MV+MV or MV+LV) nested microgrids. In this paper, healthy and faulty islanding detection of LV network connected generation unit during nested (MV+LV) microgrid islanded operation were studied by simulations with PSCAD model from real-life smart grid pilot. Main focus in the simulations was on the study and comparison of usage possibilities of combined (high-speed communication based transfer trip & fault detection/direction + voltage vector shift) and multi-criteria (voltage total harmonic distortion & voltage unbalance) based islanding detection schemes also during intended island operation of nested microgrid consisting only from inverter based generation units.fi=vertaisarvioitu|en=peerReviewed

Integration erneuerbarer Energiequellen in das Schweizer Verteilnetz: Möglichkeiten von Microgrids

Die Literaturstudie wurde von den Elektrizitätswerken des Kantons Zürich (EKZ) im Rahmen ihrer Hochschulförderung finanziell unterstützt.Microgrids sind eine vielversprechende Möglichkeit, die zunehmende Anzahl EE-Anlagen verhältnismässig kostengünstig in das bestehende Stromnetz zu integrieren. Viele technische Komponenten befinden sich jedoch noch in der Entwicklungsphase und werden erst in der Zukunft wirtschaftlich einsetzbar sein. Trotzdem werden derzeit schon verschiedene grosse Microgrids in Pilotprojekten weltweit implementiert. Offiziell und langfristig ins Netz integriert wurden bisher meist nur kleine Microgrids, typischerweise zur rudimentären Stromversorgung oder auf Gebäude- oder Campus-Ebene. Die Rolle der Verteilnetzbetreiber wird sich mit der Einführung von Microgrids erheblich ändern und erweitern, da sie damit aktiver in das Stromgeschehen eingreifen können. In der Schweiz werden die gesetzlichen Rahmenbedingungen für die Einbindung von Microgrids momentan erst noch ausgearbeitet, welche die möglichen Implementierungen von Microgrids, beispielsweise über Vergütungsanreize, in den nächsten Jahren stark beeinflussen können

Challenges, advances and future directions in protection of hybrid AC/DC microgrids

Hybrid microgrids which consist of AC and DC subgrids interconnected by power electronic interfaces have attracted much attention in recent years. They not only can integrate the main benefits of both AC and DC configurations, but also can reduce the number of converters in connection of Distributed Generation (DG) sources, Energy Storage Systems (ESSs) and loads to AC or DC buses. In this paper, the structure of hybrid microgrids is discussed, and then a broad overview of the available protection devices and approaches for AC and DC subgrids is presented. After description, analysis and classification of the existing schemes, some research directions including communication infrastructures, combined control and protection schemes, and promising devices for the realisation of future hybrid AC/DC microgrids are pointed out

Una revisión integral de la sostenibilidad en las microrredes aisladas colombianas

Context: The increase in rural electrification projects has led to the emergence of technologies that allow operating local distribution networks such as isolated microgrids. However, the successful implementation of these isolated microgrids requires that their planning, operation, monitoring, and control consider a framework that allows maintaining technical, economic, and environmental sustainability over an extended time horizon. Therefore, this paper proposes a model that allows identifying the main technical, economic, regulatory, and environmental variables that should be considered for the successful planning of Colombian rural electrification solutions. Methodology: This paper proposes the use of System Dynamics to create a model that allows describing the causal relationships between the different variables essential for the design and operation of isolated microgrids. To this effect, the identification of the related variables and their corresponding classification are presented, together with a model of theoretical expectations about their relationships. Results: A model that integrates and describes the behavior of the main variables involved in the operation of microgrids was formulated to analyze the possible implementation of policies that guarantee the sustainability of these solutions and enhance the use of renewable energy resources while improving the continuity of the electric energy supply. Conclusions: It was possible to show that operation by means of isolated microgrids with the integration of Distributed Energy Resources is a sustainable solution for rural electrification in Colombia, given that it enhances the use of generation resources with a reduced carbon footprint that are present in the territories under study. These microgrids have the potential to improve the living conditions of users by reducing unsatisfied basic needs. Funding: Universidad Nacional de Colombia – Sede Manizales.            Contexto: El aumento de los proyectos de electrificación rural ha propiciado la aparición de tecnologías que permiten operar redes de distribución local como microrredes aisladas. Sin embargo, la implementación exitosa de estas microrredes requiere que su planificación, operación, monitoreo y control considere un marco que permita mantener la sostenibilidad integral en un horizonte de tiempo extendido. Por ello, este trabajo propone un modelo que permite identificar las principales variables técnicas, económicas, regulatorias y ambientales que deben ser consideradas para la planificación exitosa de soluciones de electrificación rural en Colombia. Metodología: Este artículo propone el uso de la Dinámica de Sistemas para la creación de un modelo que permita describir las relaciones causales entre las diferentes variables que deben ser consideradas en el diseño y operación de microrredes aisladas. Para ello se presentan la identificación de las variables relacionadas, su respectiva clasificación y un modelo de expectativas teóricas sobre la relación de estas variables entre sí. Resultados: Se formuló un modelo que integra y describe el comportamiento de las principales variables involucradas en la operación de las microrredes para analizar la posible implementación de políticas que garanticen la sostenibilidad de estas soluciones y potencien el uso de recursos energéticos renovables, a la par que mejoren la continuidad del suministro de energía eléctrica. Conclusiones: Fue posible mostrar que la operación por microrredes aisladas con integración de Recursos Energéticos Distribuidos es una solución sostenible para la electrificación rural en Colombia, pues potencia el uso de los recursos de generación con huella de carbono reducida presentes en los territorios estudiados. Estas microrredes tienen el potencial de mejorar las condiciones de vida de los usuarios al disminuir las necesidades básicas insatisfechas. Financiamiento: Universidad Nacional de Colombia.      

Intelligent Protection Scheme of Electrical Energy Distribution Systems in the presence of Distributed Generation Sources using Agent-Based Distributed Controller

The ever-increasing of renewable distributed generation sources in distribution networks, as well as increasing network size, have faced agent-based protection schemes with a heavy communicational load. Accordingly, despite the fast and reliable nature of multi-agent systems, they have the possibility of improper performance, especially in centralized protection systems. This paper presents an intelligent self-healing method that has the ability to replace common multi-agent systems during fault conditions. Therefore, protection tasks are performed in a single control level, without dependence on higher communicational levels, to clear the fault. Decentralized operation of this structure is provided by using intelligent electronic devices and distributed communications. In this way, the proposed scheme is described with high-speed peer-to-peer communication capability using the IEC-61850 GOOSE protocol. Then, a penetration-free algorithm, without the help of a central controller, is provided by using GOOSE message capabilities, to prevent any electricity interruption due to insufficient protection settings. Finally, by planning different scenarios and simulating a practical distribution network via ETAP software, the accuracy of the proposed algorithm has been proven

Non-Pilot Protection of the Inverter-Dominated AC Microgrid

The main objective of this research is to develop reliable non-pilot protection and control strategies for the inverter-dominated microgrid. First, an improved Proportional-Derivative (PD) droop control strategy is proposed for enhanced disturbance response of the inverter-dominated AC microgrid. The proposed strategy significantly improves microgrid dynamic response and stability without requiring communication between distributed energy resources. Moreover, the impacts of large startup currents of induction motors on the stability and power quality of the inverter-dominated microgrid are investigates and recommendations for minimizing the associated adverse effects are made. Subsequently, a fast, selective, and reliable protection strategy for the inverter-dominated microgrid is introduced. The proposed protection strategy utilizes phase- and sequence-domain protective elements for reliable detection of symmetrical and asymmetrical faults without the need for communication signals or adaptive relays settings. The protection strategy is robust against the grid-connection mode of the microgrid and enables fuse protection of laterals. It can also be implemented on the existing commercially available relays. The acceptable performance of the proposed protection and control strategies is verified through numerous fault studies conducted on a realistic study system in the PSCAD/EMTDC software environment. Additionally, the proposed protection strategy is implemented in a SEL-351 relay and evaluated using the SEL-AMS industrial relay testing platform