An Adaptive Overcurrent Coordination Scheme to Improve Relay Sensitivity and Overcome Drawbacks due to Distributed Generation in Smart Grids

Distributed Generation (DG) brought new challenges for protection engineers since standard relay settings of traditional system may no longer function properly under increasing presence of DG. The extreme case is coordination loss between primary and backup relays. The directional overcurrent relay (DOCR) which is the most implemented protective device in the electrical network also suffers performance degradation in presence of DG. Therefore, this paper proposes the mitigation of DG impact on DOCR coordination employing adaptive protection scheme (APS) using differential evolution algorithm (DE) while improving overall sensitivity of relays . The impacts of DG prior and after the application of APS are presented based on interconnected 6 bus and IEEE 14 bus system. As a consequence, general sensitivity improvement and mitigation scheme is proposed

INTELLIGENT METHODS FOR OPTIMUM ONLINE ADAPTIVE COORDINATION OF OVERCURRENT RELAYS

During the operation in a modern power distribution system, some abnormal events may happen, such as over-voltage, faults, under-frequency and overloading, and so on. These abnormal events may cause a power outage in a distribution system or damages on the equipment in a distribution system. Hence these abnormal events should be identified and isolated by protection systems as quickly as possible to make sure we can maintain a stable and reliable distribution system to supply adequate electric power to the largest number of consumers as we can. To sum up, we need stable and reliable protection systems to satisfy this requirement. Chapter 1 of the dissertation is a brief introduction to my research contents. Firstly, the background of a distribution system and the protection systems in a power system will be introduced in the first subchapter. Then there will be a review of existing methods of optimum coordination of overcurrent relays using different optimal techniques. The dissertation outline will be illustrated in the end. Chapter 2 of the dissertation describes a novel method of optimum online adaptive coordination of overcurrent relays using the genetic algorithm. In this chapter, the basic idea of the proposed methods will be explained in the first subchapter. It includes the genetic algorithm concepts and details about how it works as an optimal technique. Then three different types of simulation systems will be used in this part. The first one is a basic distribution system without distributed generations (DGs); the second one is similar to the first one but with load variations; the last simulation system is similar to the first one but with a distributed generation in it. Using three different simulation systems will demonstrate that the coordination of overcurrent relays is influenced by different operating conditions of the distribution system. In Chapter 3, a larger sized distribution system with more distributed generations and loads will be simulated and used for verifying the proposed method in a more realistic environment. In addition, the effects of fault location on the optimum coordination of overcurrent relays will be discussed here. In Chapter 4, the optimal differential evolution (DE) technique will be introduced. Because of the requirement of the online adaptive function, the optimal process needs to be accomplished as soon as possible. Through the comparison between genetic algorithm and differential evolution on the optimum coordination of overcurrent relays, we found that differential evolution is much faster than the genetic algorithm, especially when the size of the distribution system grows. Therefore, the differential evolution optimal technique is more suited than the genetic algorithm to realize online adaptive function. Chapter 5 presents the conclusion of the research work that has been done in this dissertation

Artificial intelligence-based protection for smart grids

Lately, adequate protection strategies need to be developed when Microgrids (MGs) are connected to smart grids to prevent undesirable tripping. Conventional relay settings need to be adapted to changes in Distributed Generator (DG) penetrations or grid reconfigurations, which is a complicated task that can be solved efficiently using Artificial Intelligence (AI)-based protection. This paper compares and validates the difference between conventional protection (overcurrent and differential) strategies and a new strategy based on Artificial Neural Networks (ANNs), which have been shown as adequate protection, especially with reconfigurable smart grids. In addition, the limitations of the conventional protections are discussed. The AI protection is employed through the communication between all Protective Devices (PDs) in the grid, and a backup strategy that employs the communication among the PDs in the same line. This paper goes a step further to validate the protection strategies based on simulations using the MATLABTM platform and experimental results using a scaled grid. The AI-based protection method gave the best solution as it can be adapted for different grids with high accuracy and faster response than conventional protection, and without the need to change the protection settings. The scaled grid was designed for the smart grid to advocate the behavior of the protection strategies experimentally for both conventional and AI-based protections.This work is supported by Li Dak Sum Innovation Fellowship Funding (E06211200006) from the University of Nottingham Ningbo China.Peer ReviewedPostprint (published version

Application of optimization techniques to solve overcurrent relay coordination.

Masters Degree. University of KwaZulu- Natal, Durban.Distribution systems continues to grow and becoming more complex with increasing operational challenges such as protection miscoordination. Initially, conventional methods were favoured to optimize protection coordination; however, the implementation process is laborious and time-consuming. “Therefore, recent studies have adopted the utilisation of particle swarm optimization and genetic algorithms to solve overcurrent relay coordination problems and maximise system selectivity and operational speed. Particle swarm optimization and genetic algorithms are evolutionary algorithms that at times suffer from premature convergence due to poor selection of control parameters. Consequently, this thesis aims to present a comprehensive sensitivity analysis to evaluate the effect of the discrete control parameters on the performance of particle swarm optimizer and genetic algorithms, alternatively on the behaviour of overcurrent relays. The main objectives of this research work also include modelling and simulation of distribution system protection scheme, employment of evolutionary algorithms with control parameters that perform efficiently and effectively to maximise protection coordination between relays, optimize relay operating time and maintain the stipulate coordination time interval, and lastly, to outline future recommendations. The distribution network understudy was modelled and simulated on a real-time digital simulator to validate protection settings, and the verification of evolutionary algorithms performance was displayed on Matlab/Simulink. An extensive parametric sensitivity analysis was conducted to understand the impact of the individual control parameters and their respective influence on the performance of evolutionary algorithms. The findings indicate that particle swarm optimization is more sensitive to inertia weight and swarm size while the number of iterations has minimal effect. The results also depict that genetic algorithms’ performance is mostly influenced by crossover probability, mutation probability, and population size. Sensitivity analysis results were verified by comparing the performance of particle swarm optimizer with genetic algorithms, which demonstrated that particle swarm optimization performs efficiently and robustly in solving the considered problem, especially in terms of convergence speed. Furthermore, overcurrent relays were more sensitive, selective, and the operational speed was reduced for particle swarm optimizer compared to other algorithms. The optimal protection coordination achieved using particle swarm optimization showed superiority of the algorithm, its ability to circumvent premature convergence, consistency, and” efficiency

Optimal relay coordination of an adaptive protection scheme using modified PSO algorithm.

Recently, future smart grids are described by a dominantly fluctuating character due to the power consumption change from peak to off-peak loading conditions, the operation of micro-grids in grid-connected or islanded mode and other possible network topologies resulting in an effective change in network impedances and short circuit current level. Therefore, the situation from protection sensitivity, selectivity and speed may become more and more challenging. In this paper, Adaptive protection scheme is proposed to respond to structural variations occurred in interconnected power systems. A designed software based on Modified Particle Swarm Optimization (MPSO) algorithm is suggested to solve the relay coordination problem in modern distribution networks. In this study, the 14 IEEE bus system is tested via three power system scenarios showing the effect of adding and disconnecting of DG units and the occurrence of sudden line outages on the system. The obtained results show that the proposed algorithm has achieved optimum relay settings for each existing network topology

Optimal protective relaying scheme of distributed generation connected distribution network using particle swarm optimization-gravitational search algorithm technique

This paper develops particle swarm optimization integrated with gravitational search algorithm (PSO-GSA) to coordinate the relays in a distribution system with distributed generation (DG) connectivity. This algorithm combines PSO and GSA to improve the performance of the relay protection system. To prevent relay malfunctions following DG penetration, a suitable primary and backup relay is chosen. The PSO-GSA is coded using MATLAB software and tested on an IEEE 4-bus system simulated in Simulink. Results indicate that, when compared to using regular PSO and GSA procedures individually, the PSO-GSA technique reduces the operating time of the relay significantly

Protection of Electrical Power Systems with Full Penetration of Converter-Interface Generation

Mención Internacional en el título de doctorSince the advent of generation with converter-interface, mainly wind and solar photovoltaic (PV), power system operators have deal with some problems to maintain system stability and security. However, due to its low penetration in the system, it had barely any consequences and its study lack of interest. But over the years the generation scheme has changed, and converter-interface generators have been increasing their presence due to their low energy costs and policies against climate change. When the penetration rate is 100 %, protection systems have detection problems in the overcurrent scheme and pick-up problems in the distance scheme, jeopardising the safety of the electrical power system. This thesis proposes to use the Wavelet transform analysis method to solve these problems in full penetration scenarios of converter-interface generation. It can detect high and low frequency variations in voltage and current signals, and classify them in time and magnitude when they occur. In order to be able to propose a satisfactory solution, this thesis has carried out a study of the main key factors to be considered for fault detection. Analysing the differences between synchronous generators and generators with converter-interface, and the consequences of each of them for the protection systems. Describing the main converter control architectures and defining the equivalent model of converter short-circuit. Introducing the different types of faults in power systems. And describing the fundamental criteria for protection, and the most common protection schemes. The model used to obtain the results and check the feasibility of the proposal is the IEEE nine-bus system in a ring layout. It has been modelled including all power system elements (transmission lines, transformers, and loads) and both generation technologies (synchronous generators and converter-interface generators). In addition, the converter control strategy and its current limiting have also been considered. The results show a correct and immediate fault detection.Desde la aparición de los sistemas de generación de energía eléctrica con interfaz de convertidor electrónico, mayoritariamente eólica y solar fotovoltaica, los operadores de red han tenido que lidiar con los diferentes problemas que estos provocan para mantener la estabilidad y la seguridad del sistema. Aunque debido a su baja penetración en el sistema apenas tenía consecuencias y su estudio carecía de interés. Pero con el paso de los años ha ido cambiando el esquema de generación y los generadores con interfaz de convertidor electrónico han ido incrementando su presencia debido a sus bajos costes de la energía y a las políticas de lucha contra el cambio climático. Cuando se alcanzan niveles de penetración del 100 %, los sistemas de protección tienen problemas de detección en el esquema de sobrecorriente y de arranque en el esquema de distancia, poniendo en riesgo la seguridad del sistema eléctrico. Esta tesis propone utilizar el método de análisis de la transformada de Wavelet para solventar estos problemas en escenarios con máxima penetración de generación con interfaz de convertidor. El cual permite detectar variaciones de alta y baja frecuencia en las señales de tensión y de corriente, y clasificarlas tanto en tiempo como en tamaño cuando se producen. Para poder presentar una solución con garantías de ser satisfactoria, en esta tesis se ha realizado un estudio de los principales factores clave para tener en cuenta para la detección de faltas. Analizando las diferencias entre generadores síncronos y generadores con interfaz de convertidor electrónico, y qué consecuencias tiene cada uno de ellos para los sistemas de protección. Describiendo las principales arquitecturas de control de convertidores y definiendo los modelos equivalentes de cortocircuito del convertidor. Presentando los diferentes tipos de faltas en los sistemas eléctricos. Y describiendo los criterios fundamentales de las protecciones y los esquemas de protección más comunes. El modelo utilizado para la obtención de los resultados y comprobar la viabilidad de la propuesta es el sistema de nueve nudos del IEEE dispuesto en anillo. El cual ha sido modelado incluyendo todos los elementos del sistema (líneas de transmisión, transformadores y cargas) y ambas tecnologías de generación (generadores síncronos y generadores con interfaz de convertidor electrónico). Además, también se ha tenido en cuenta la estrategia de control del convertidor y su limitación de corriente. Los resultados muestran una correcta e inmediata detección de la falta.Programa de Doctorado en Ingeniería Eléctrica, Electrónica y Automática por la Universidad Carlos III de MadridPresidenta: Mónica Chinchilla Sánchez.- Secretario: Joaquín Eloy-García Carrasco.- Vocal: Roberto Lorenzo Alves Baraciart

Microgrid Protection Systems

Micro grids are miniature version of conventional large power grids functioning either autonomously or with inter connection to the main grid. Primary function of micro grid is to serve power at distribution level. Distributed energy resources (DERs) connected to the micro grid enables reliable and efficient operation of micro grid. Protection of micro grids assumed importance due to increased penetration of distributed energy resources. Most of the distribution systems in earlier days are radial in nature and protection systems are designed for that. These protection systems pose serious challenges when applied to present day distribution systems which are mesh connected and fed by the distributed energy resources. Limitation of the conventional protection scheme demands new insights and methodologies for micro grid protection. Due to intermediate current injection from DERs the conventional coordination of over current (O/C) relays is not possible. Further in meshed systems the fault current flow is bidirectional. Hence the protection of micro grid systems with DERs require different approach to ensure faults are cleared in less time and minimal number of consumers connected to the system are affected. A comprehensive analysis of the suitable techniques applicable for micro grid protection is presented in this chapter

Hardware-In-Loop Evaluation of Microgrid Protection Schemes

Distributed energy resources are becoming more common in distribution systems. Higher energy prices and increased interest in alternative energy sources are two of the driving forces behind this trend. Local utilities, however, anticipate very serious distribution system protection problems resulting from high penetration of these resources. The microgrid concept has been proposed as a possible solution to integrating distributed energy resources without adversely impacting the distribution system. Protection schemes have been proposed to work within this microgrid structure, but very little testing with real hardware is available. Without a practical solution for microgrid protection, backed by extensive studies, microgrids are unlikely to receive wide acceptance. This thesis outlines modeling of microgrids for protection testing using a real time digital simulator. In addition, the construction of a low voltage, low power, hardware-in-loop test bed using relays and an automation controller is detailed. The results of testing possible microgrid protection schemes using this apparatus are presented along with conclusions and suggestions for future work

Real time coordination of overcurrent relays by means of optimization algorithm.

Protection is widely used in all different voltage levels of the electrical power system: generation, transmission, sub-transmission and distribution etc. An overcurrent relay is a protection that is widely implemented in the sub-transmission and distribution systems due to its competing cost. Depending on the operative conditions and fault locations in a mesh system, the load or fault currents can circle in or out of the overcurrent relay's protective zone. Hence directional overcurrent relays are used to discriminate whether the fault is located in or out of the protective zone. The propose of coordinating the overcurrent relays is to encounter settings that minimize the operation time for faults within the protective zone and at the same time offering pre-specified timed backup for relays that are in the adjacent zones. So the maximum fault current that the relay detects in its protective zone must be greater than the fault currents in the adjacent zones. The above condition is met in radial systems, one source mesh systems and two source mesh systems where the sources are located symmetrically at the end. But the above condition is not always met in the multi-source mesh systems due to the numerous operative configurations. Since the systems cannot operate in the absence of protection, other protection principles must be used, i.e. impedance relay. It is then said that for certain operative configurations of mesh system, overcurrent protection principle is out of range or in other words reaches the limit of its protection principle [1]