During recent decades with the power system restructuring process, centralized energy sources are being replaced with decentralized ones. This phenomenon has resulted in a novel concept in electric ...power systems, particularly in distribution systems, known as Distributed Generation (DG). On one hand, utilizing DG is important for secure power generation and reducing power losses. On the other hand, widespread use of such technologies introduces new challenges to power systems such as their optimal location, protection devices' settings, voltage regulation, and Power Quality (PQ) issues. Another key point which needs to be considered relates to specific DG technologies based on Renewable Energy Sources (RESs), such as wind and solar, due to their uncertain power generation. In this regard, this paper provides a comprehensive review of different types of DG and investigates the newly emerging challenges arising in the presence of DG in electrical grids.
•Proposing a comprehensive review on Distributed Generations (DGs).•Investigating the impact of DGs on the protection of distribution systems.•Reviewing the voltage regulation methods in the presence of DGs.
This paper proposes a communication assisted dual setting relay protection scheme for micro-grids with grid connected and islanded capability. Previous work on dual setting relays has been applied to ...grid connected distributed generation systems only, but one major shortcoming is the failure of the backup scheme to operate in a coordinated manner. The proposed scheme relies on the use of dual setting directional overcurrent relays that are capable of operating in both forward and reverse directions, with different settings, and with a low bandwidth communication to maintain proper protection coordination. The problem is formulated as a non-linear constrained programming problem where the relay settings are optimally determined to minimize the overall relay operating time for primary and backup operation. The scheme is tested on a modified version of the IEEE 30 bus test system equipped with distributed generation and with capability of operating in an islanded mode. The proposed scheme is compared against the conventional scheme and the results show that it is capable of overcoming the problem of infeasibility, experienced by the conventional method, without the need of installing fault current limiters. Furthermore, it achieves remarkable reduction in both the primary and backup relay operating times, which was reflected in a reduction in the total relay operating time.
•Advancing the state-of-the-art microgrid protection research.•A critical review on AC microgrid protection issues.•A critical review on AC microgrid protection challenges.•A critical review on AC ...microgrid protective solutions.•A critical Discussion on open research issues and recommendation for future scope.
Microgrid is an important component of the evolving smart-grid. It has the ability to increase reliability, decrease costs, and enlarge penetration rates for distribution generation systems. However, the protection coordination may get badly affected due to the bi-directional/variable power flow associated with microgrid system and increasing penetration rates of distributed energy resources. Therefore, a proper protection strategy is highly required to decrease the complexities associated with microgrid system. In this paper, a widespread literature review on the current research and progression in the field of AC-microgrid protection is presented. The prime objective of this survey is to extend the researcher’s database comprising relevant reference points which could be highly beneficial to their future research work. This work comprises of the current status, major hitches and existing research efforts focussed in the direction of providing a smooth relaying system under diverse MG operating conditions. Moreover, the work concentrates on analysing the intelligent approaches/devices that help transform the present protection schemes to become smarter.
Integration of distributed energy resources in power networks make them interconnected and active. Depending upon the type, short circuit capability and location of distributed energy resource in ...transmission and distribution systems, design of protection coordination schemes becomes very challenging. Complexity further increases in the design of protection coordination schemes, when penetration effect of these resources reaches to upstream transmission lines and coordination among the distance and over current relays requires a review. The protection coordination scheme discussed in this article monitors the state of power network continuously. Depending upon the operational topology of the network, time dial settings as well as plug settings of over current relays and zone-2 setting of distance relays are selected from pre-optimsed relay group settings. Whenever there is any change in the network fault level either due to change in line parameters or incoming of new distributed energy resource, new relay group settings are communicated to corresponding relays. The proposed protection coordination scheme is implemented in RSCAD software for modified eight bus test bus and modified IEEE14 bus system. It is observed that the proposed protection approach is highly flexible to maintain the coordination among the over current and distance relays.
This review paper is focused on the impact of distributed generation (DG) on distribution system protection. The integration of DG is transforming the traditional radial distribution system into a ...multi-source system that requires protection that is capable of maintaining proper coordination under bi-directional and variable power flow conditions. The multiple types of DGs with different short circuit characteristics mean that the protection must also be effective under conditions of unpredictable fault currents. New grid code requirements demand that DGs remain connected under fault conditions to provide grid support and improve system reliability and security of supply. A discussion is given of the traditional protection techniques for the distribution system and the shortcomings of such techniques when DGs are integrated into the system. The paper also presents a wide survey and review of recent techniques proposed by various researchers to mitigate the effects of DG integration on the performance of distribution system protection. Centralised and distributed techniques have been proposed that include deployment of intelligent smart devices and communication systems to enhance and provide novel ideas for solving the protection problem. The implementation challenges of these techniques are discussed and proposals for the future given.
Nowadays, distributed generations (DGs) and microgrids play a significant role in development of power systems, but DGs produce several protection problems especially in optimal coordination of ...directional overcurrent relays (DORs). Optimal coordination of DORs is a highly constrained nonlinear programming problem, which has attracted attention of many research studies in recent years. Cuckoo optimization algorithm (COA) is introduced as an optimization tool based on behavior patterns of Cuckoos. In this paper, COA and linear programming (LP) are combined as a new hybrid COA-LP optimization algorithm in order to optimize the coordination protection of DORs in microgrids and find the optimum value of fault current limiter at the point of common coupling. The optimum settings of DORs are obtained for both modes of operation: 1) grid-connected and 2) island mode. The proposed algorithm is applied to Canadian distribution benchmark and a modified IEEE 14 bus networks and compared with particle swarm optimization (PSO) and genetic algorithm (GA). The obtained results show that the computational efficiency of the proposed COA-LP is better than PSO and GA in terms of speed and total operating time of DORs.
The operation of multiple microgrids (MGs) with distribution system enhances reliability and resiliency of the power supply significantly by enabling high penetration of locally available distributed ...energy resources (DERs). However, there are several issues in the proper operation of multiple MGs that need to be addressed. Providing proper protection coordination is one of the most important issues in the coordinated operation of networked MGs (NMGs). In this study, an efficient protection coordination scheme for NMGs is proposed by utilising the commonly used numerical directional overcurrent relays (DOCRs) with single and dual settings. Issues related to the operation of NMGs such as the change in network topology, connection status of the point of common coupling and low voltage fault ride through of DERs have been considered. The protection coordination problem has been formulated as an optimisation problem and solved using the interior point method. The proposed protection coordination scheme of NMGs has been tested on the 69-bus radial distribution system with the integration of three MGs, which is not reported in earlier literature. The suitability and effectiveness of the proposed DOCRs coordination scheme have been demonstrated.
•A proposed design of a hierarchical protection scheme is presented.•Protective devices are optimally coordinated based on fault current transients.•Hybrid superconducting fault current limiters are ...optimally allocated to keep coordination under synchronous and inverter-based wind DGs.•Ride-through capability of wind DGs is integrated into the fault current limiter sizing problem.•Changes of network topology and variation of detected fault current are considered.
A combined protection system has multiple types of devices such as directional overcurrent relays, reclosers, and fuses to protect distinct areas in a DG-incorporated network. An approach for setting all protective devices to realize complete coordination of adjacent ones taking transient responses into account is presented. The participation of synchronous generator-based and/or inverter-based wind DGs can degrade protection coordination. So, a scheme for sustaining coordination by optimal hybrid superconducting fault current limiters is proposed. The scheme can cope with variation of network topology; and handles the change of fault current level perceived by the protection device under a given topology. Moreover, instead of the conventional steady-state models, more realistic dynamic models of relays, reclosers, DGs, and fault current limiter are used. As a serious operation problem, undesired tripping of wind DGs under fault condition can occur due to the sag of terminal voltage below certain limits defined by national and international standards. Therefore, the proposed scheme prevents this undesired tripping of wind DGs by integrating its ride-through capability constraints into the fault current limiter allocation problem. The proposed approach is applied to the IEEE 9-bus and 30-bus systems. Results confirm the efficacy of the proposed method.
The facility to save multiple setting groups (SGs) within digital overcurrent relays (OCRs) is to adapt the active setting of the relays to the current topology of the power network. However, the ...number of available SGs is much lower than the possible topologies of the network, so this facility is usually applied to a few local changes in the network. This paper aims to extend the application to a complete set of topologies. A proper index is introduced and applied with a k -means clustering technique to classify the topologies into some clusters, whose number is equal to the number of SGs. Then, for every topology cluster, the optimal settings are calculated and saved in the OCRs as a distinct SG to be activated by changing the topology to any member of the cluster. Applying this technique to OCRs of the IEEE 14-bus test network and a 63/20kV substation verifies its effectiveness on reserving coordination for all topologies and reducing the relays' time dial setting. Using available communication links, this technique can be implemented by making a computer network between substations of the power network without needing to interact with the control center.
With the integration of distributed generation (DG) to meshed distribution systems, the operating time of the protective system becomes a major concern in order to avoid nuisance DG tripping. This ...paper proposes a new time-current-voltage tripping characteristic for directional overcurrent relays (DOCRs) that can achieve a higher possible reduction of overall relays operating time in meshed distribution networks. The proposed tripping characteristic is described in detail. Moreover, the protection coordination problem is formulated as a constrained nonlinear programming problem to determine the optimal relay settings. The proposed characteristic is tested on the power distribution system of the IEEE 14 bus and IEEE 30 bus with inverter-based and synchronous-based DG units. The outcome of this study reveals that the new tripping characteristic for DOCRs achieves notable reduction in total relays' operating time over the conventional characteristic.
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