Overcurrent relays coordination optimisation methods in distribution systems for microgrids: a review

Electric power networks connected with multiple distributed generations (microgrids) require adequate protection coordination. In this paper, the overcurrent relay coordination concept in distribution system has been presented with details. In this available literature, the previous works on optimisation methods utilised for the coordination of over current relays; classification has been made based on the optimisation techniques, non-standard characteristics, new constraints that have been proposed for optimal coordination and dual setting protection schemes. Then a comprehensive review has been done on optimisation techniques including the conventional methods, heuristic and hybrid methods and the relevant issues have been addressed

Optimal Overcurrent Relays Coordination using an Improved Grey Wolf Optimizer

Recently, nature inspired algorithms (NIA) have been implemented to various fields of optimization problems. In this paper, the implementation of NIA is reported to solve the overcurrent relay coordination problem. The purpose is to find the optimal value of the Time Multiplier Setting (TMS) and Plug Setting (PS) in order to minimize the primary relays’ operating time at the near end fault. The optimization is performed using the Improved Grey Wolf Optimization (IGWO) algorithm. Some modifications to the original GWO have been made to improve the candidate’s exploration ability. Comprehensive simulation studies have been performed to demonstrate the reliability and efficiency of the proposed modification technique compared to the conventional GWO and some well-known algorithms. The generated results have confirmed the proposed IGWO is able to optimize the objective function of the overcurrent relay coordination problem

Omega grey wolf optimizer (ωGWO) for optimization of overcurrent relays coordination with distributed generation

Inverse definite minimum time (IDMT) overcurrent relays (OCRs) are among protective devices installed in electrical power distribution networks. The devices are used to detect and isolate the faulty area from the system in order to maintain the reliability and availability of the electrical supply during contingency condition. The overall protection coordination is thus very complicated and could not be satisfied using the conventional method moreover for the modern distribution system. This thesis apply a meta-heuristic algorithm called Grey Wolf Optimizer (GWO) to minimize the overcurrent relays operating time while fulfilling the inequality constraints. GWO is inspired by the hunting behavior of the grey wolf which have firm social dominant hierarchy. Comparative studies have been performed in between GWO and the other well-known methods such as Differential Evolution (DE), Particle Swarm Optimizer (PSO) and Biogeographybased Optimizer (BBO), to demonstrate the efficiency of the GWO. The study is resumed with an improvement to the original GWO’s exploration formula named as Omega-GWO (ωGWO) to enhance the hunting ability. The ωGWO is then implemented to the realdistribution network with the distributed generation (DG) in order to investigate the drawbacks of the DG insertion towards the original overcurrent relays configuration setting. The GWO algorithm is tested to four different test cases which are IEEE 3 bus (consists of six OCRs), IEEE 8 bus (consists of 14 OCRs), 9 bus (consists of 24 OCRs) and IEEE 15 bus (consists of 42 OCRs) test systems with normal inverse (NI) characteristic curve for all test cases and very inverse (VI) curve for selected cases to test the flexibility of the GWO algorithm. The real-distribution network in Malaysia which originally without DG is chosen, to investigate and recommend the optimal DG placement that have least negative impact towards the original overcurrent coordination setting. The simulation results from this study has established that GWO is able to produce promising solutions by generating the lowest operating time among other reviewed algorithms. The superiority of the GWO algorithm is proven with relays’ operational time are reduced for about 0.09 seconds and 0.46 seconds as compared to DE and PSO respectively. In addition, the computational time of the GWO algorithm is faster than DE and PSO with the respective reduced time is 23 seconds and 37 seconds. In Moreover, the robustness of GWO algorithm is establish with low standard deviation of 1.7142 seconds as compared to BBO. The ωGWO has shown an improvement for about 55% and 19% compared to other improved and hybrid method of GA-NLP and PSO-LP respectively and 0.7% reduction in relays operating time compared to the original GWO. The investigation to the DG integration has disclosed that the scheme is robust and appropriate to be implemented for future system operational and topology revolutions

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

Sistema automatizado para coordenação de ajustes de proteção de sobrecorrente direcional em sistemas malhados

Orientadora: Prof.ª. Dra. Thelma S. P. FernandesCoorientador: Prof. Dr. Mateus Duarte TeixeiraDissertação (mestrado) - Universidade Federal do Paraná, Setor de Tecnologia, Programa de Pós-Graduação em Engenharia Elétrica. Defesa : Curitiba, 17/12/2021Inclui referências: p. 88-90Resumo: Para que um Sistema Elétrico de Potência opere satisfatoriamente, deve haver uma adequada coordenação do sistema de proteção, que é feita através de parametrização de ajustes de relés de proteção. Essa parametrização envolve estudos relacionados aos cálculos de correntes de curto-circuito, seletividade e coordenação entre os dispositivos de proteção. Esses estudos devem garantir que os sistemas de proteção operem no menor tempo possível e desliguem o mínimo de circuitos possíveis, ou seja, que os relés de proteção mais próximos da ocorrência do curto-circuito operem mais rapidamente do que os relés das linhas adjacentes. Por ser uma tarefa complexa, esse trabalho propõe que a obtenção desses parâmetros de ajustes, relacionados especificamente a relés de sobrecorrente instalados em sistemas malhados, seja feita utilizando um processo de otimização. Os parâmetros de entrada do problema de otimização são os valores de impedâncias de sequência das linhas de transmissão, geradores e transformadores que compõem o sistema elétrico. A partir desses dados são simulados alguns casos de curto-circuito que são necessários para inicializar o processo de otimização dos parâmetros de ajustes de sobrecorrente direcional de neutro instantâneo (67NI) e sobrecorrente direcional de neutro temporizado (67NT) em todos os terminais de linha do sistema em análise. A otimização envolve o ajuste de tempo de atuação dos relés temporizados 67NT que é dado por curvas inversas padronizadas, time dial (TDS) e corrente de Pick-up (IPS). Portanto, os parâmetros de ajuste do 67NT têm 3 variáveis que devem ser ajustadas: tipo de curva, TDS e IPS. A formulação do problema de otimização proposto para realização dos ajustes ótimos é resolvida via Algoritmos Genéticos e foi testada utilizando sistemas de 5 e 30 barras. Foi testada a coordenação de várias combinações desses ajustes até obter os valores ótimos coordenados para todos os relés dos sistemas testados.Abstract: For an Electric Power System to operate satisfactorily there must be an adequate coordination of the protection system, which is done through parameterization of protection relay settings. This parameterization involves studies related to the calculation of short-circuit currents, selectivity and coordination between protection devices. These studies must ensure that the protection systems operate in the shortest time possible and disconnect as few circuits as possible, that is, that the protection relays closest to the occurrence of the short circuit operate faster than the relays in the adjacent lines. As it is a complex task, this work proposes that the obtaining of these adjustment parameters, specifically related to overcurrent relays installed in meshed systems, be done using an optimization process. The input parameters of the optimization problem are the sequence impedance values of the transmission lines, generators and transformers that make up the electrical system. From these data, some short-circuit cases are simulated that are necessary to start the optimization process of the instantaneous directional overcurrent (67NI) and timed directional overcurrent (67NT) adjustment parameters in all the line terminals of the system under analysis. The optimization involves adjusting the actuation time of the 67NT timed relays which is given by standardized inverse curves, time dial (TDS) and Pick-up current (IPS). Therefore, the 67NT adjustment parameters have 3 variables that must be adjusted: curve type, TDS and IPS. The formulation of the optimization problem proposed to perform the optimal fits is solved via Genetic Algorithms and was tested using 5 and 30 bus systems. Coordination of various combinations of these settings was tested until the optimal coordinated values were obtained for all relays in the tested systems