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

Adaptive overcurrent protection application for a micro-grid system in South Africa

Abstract: The non-directional overcurrent protection (International Electrotechnical Commission standard IEC 617 or American National Standards Institute ANSI/Institute of Electrical and Electronic Engineers IEEE C37.2 standard device number 51) is one protection type/relay function that has stood the test of time. The latest generation of relays has brought about enhanced capabilities. The most popular overcurrent protection, which is the Inverse Definite Minimum Time (IDMT) function, has proven to provide coordination of electrical nodes with ease. This is one of the oldest but extremely reliable relay characteristic. A number of new protection functions and enhancements to existing functions are commensurate to the advanced technical capabilities of the newer generation protective devices. The new development techniques include “acceleration”, which is a technique of sending the circuit breaker status of the near end of a line or feeder to the far end to influence the relay decision at the far end. Impedance protection, unit line protection, etc. have come with many advanced characteristics and properties. The enhancements to protection devices bear special features but cannot substitute inverse time overcurrent protection, which, up to now, is a reliable backup in feeder protection schemes in South Africa. The superior feature is the capability to achieve coordination between a series of protective devices. This is achievable without excessive damage to the electrical components of the circuit...M.Ing. (Electrical Engineering

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

Real time adaptive relay settings for Microgrid protection verified using Hardware in Loop

Microgrids with penetration of renewables is imposing new challenges for system protection. Renewables are characterized with high source impedance which limit the short circuit current. The value of short-circuit current is limited due to converters used which limit the current to a maximum of 1.1 to 1.5 times maximum rated load current. This can result in faults during the islanded mode of microgrid to go unnoticed if the relay settings are not adapted to account for it. The presence of such uncleared faults in the microgrid can result in exposing it to overcurrent for a long time which can damage the equipment. One solution is to have different protection element pickup settings for different modes of operation. This report discusses the development of an algorithm to switch these settings upon microgrid state changes and test the algorithm using OPAL-RT hardware in loop real-time testing with SEL-351S relay as the hardware

Recent Developments and Challenges on AC Microgrids Fault Detection and Protection Systems–A Review

The protection of AC microgrids (MGs) is an issue of paramount importance to ensure their reliable and safe operation. Designing reliable protection mechanism, however, is not a trivial task, as many practical issues need to be considered. The operation mode of MGs, which can be grid-connected or islanded, employed control strategy and practical limitations of the power electronic converters that are utilized to interface renewable energy sources and the grid, are some of the practical constraints that make fault detection, classification, and coordination in MGs different from legacy grid protection. This article aims to present the state-of-the-art of the latest research and developments, including the challenges and issues in the field of AC MG protection. A broad overview of the available fault detection, fault classification, and fault location techniques for AC MG protection and coordination are presented. Moreover, the available methods are classified, and their advantages and disadvantages are discussed

Optimal overcurrent relay coordination in wind farm using genetic algorithm

Wind farms are ones of the most indispensable types of sustainable energies which are progressively engaged in smart grids with tenacity of electrical power generation predominantly as a distribution generation system. Thus, rigorous protection of wind power plants is an immensely momentous aspect in electrical power protection engineering which must be contemplated thoroughly during designing the wind plants to afford a proper protection for power components in case of fault occurrence. The most commodious protection apparatus are overcurrent relays (OCRs) which are responsible for protecting power systems from impending faults. In order to employ a prosperous and proper protection for wind farms, these relays must be set precisely and well-coordinated with each other to clear the faults at the system in the shortest possible time. These relays are set and coordinated with each other by applying IEEE or IEC standards methods, however, their operation times are relatively long and the coordination between these relays are not optimal. The other common problem in these power systems is when a fault occurs in a plant, several OCRs operate instead of a designated relay to that particular fault location. This, if undesirable can result in unnecessary power loss and disconnection of healthy feeders out of the plant which is extremely dire. It is necessary to address the problems related inefficient coordination of OCRs. Many suggestions have been made and approaches implemented, however one of the most prominent methods is the use of Genetic Algorithm (GA) to improve the function and coordination of OCRs. GA optimization technique was implemented in this project due to its ample advantages over other AI techniques including proving high accuracy, fast response and most importantly obtaining optimal solutions for nonlinear characteristics of OCRs. In addressing the mentioned problems, the main objective of this research is to improve the protection of wind farms by optimizing the relay settings, reducing their operation time, Time Setting Multiplier (TSM) of each relay, improving the coordination between relays after implementation of IEC 60255-151:2009 standard. The most recent and successful OF for GA technique has been used, unique parameters for GA was selected for this research to significantly improve the protection for wind farms that is highly better compared to any research accomplished before for the purpose of wind farm protection. GA was used to obtain improved values for each relay settings based on their coordination criteria. Each relay operation time and TSM are optimized which would contribute to provide a better protection for wind farm. Thus, the objective of this work which is improving the protection of wind farms by optimizing the relay settings, reducing their operation time, Time Setting Multiplier (TSM) of each relay, improving the coordination between relays, have been successfully fulfilled and solved the problems associated with wind farm relay protection system settings. The new approach has shown significant improvement in operation of OCRs at the wind farm, have drastically reduced the accumulative operation time of the relays by 26.8735% (3.7623 seconds)

A review on protection issues in micro-grids embedded with distribution generations

© 2017 IEEE. According to recent developments, the application of distributed generations (DGs) has become popular especially in distribution systems. The high utilization of distributed generating resources in modern power systems can cause new challenges from protection coordination perspectives. Changing the distribution system structure from single-supply radial system to multi-source ring network, leads to the bidirectional power flow and also has a vital impact on protection coordination issues. In addition, micro-grids can be operated under grid-connected as well as islanded mode, and fault current is extensively different for these two operation modes. Therefore, traditional protection algorithms cannot be used in the advancement of power systems. In recent years, several research studies have been conducted to investigate the improvement of protection schemes in micro-grids. This paper presents a comprehensive review on protection problems resulting from micro-grids embedded with DGs, and discusses some alternate protection strategies

System configuration, fault detection, location, isolation and restoration: a review on LVDC Microgrid protections

Low voltage direct current (LVDC) distribution has gained the significant interest of research due to the advancements in power conversion technologies. However, the use of converters has given rise to several technical issues regarding their protections and controls of such devices under faulty conditions. Post-fault behaviour of converter-fed LVDC system involves both active converter control and passive circuit transient of similar time scale, which makes the protection for LVDC distribution significantly different and more challenging than low voltage AC. These protection and operational issues have handicapped the practical applications of DC distribution. This paper presents state-of-the-art protection schemes developed for DC Microgrids. With a close look at practical limitations such as the dependency on modelling accuracy, requirement on communications and so forth, a comprehensive evaluation is carried out on those system approaches in terms of system configurations， fault detection, location, isolation and restoration