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In last few decades, microgrid has emerged an interesting and intelligent approach by containing its prospective framework using smart grid protocols. One of the technical issues in implementing microgrid in smart grid environment is to design a distinct protection scheme with the ability to meet the protection requirement in all modes of operation. The motive for this study is to address a technical outlook in protection strategies of microgrid and the challenges to achieve them. Initially, the currently existing protection techniques of AC microgrid followed by DC microgrid are discussed. Since the conventional protection technique cannot be used in DC microgrid directly as there's no zero crossing in DC systems and bidirectional power flow, it needs more attention in proposing a protection strategy for DC. Therefore, this leads to the innovation of adaptive protection in microgrid where the implementation of communication infrastructure makes the system smart. Thus, this paper focuses on detailed literature on protection scheme for AC and DC microgrid. [ABSTRACT FROM AUTHOR]

The advancements in smart grid technologies had brought forth the prospect of self-healing distribution grid through intentional islanding, aided by the steadily rising penetration of inverter-based distributed generations (IBDGs). Adaptive protection is the key enabler for this resilient grid architecture. For cost-effectiveness, overcurrent relays (OCRs) with adaptive features had been proposed, often with the sensitivity problem due to low short-circuit current magnitude from the IBDG taken into consideration and largely addressed. However, apart from this widely discussed sensitivity problem, there is an underlying issue on selectivity of the OCR which is frequently disregarded when designing an adaptive overcurrent protection scheme for IBDG dominated microgrid. This selectivity problem is mainly caused by the current diversion to load during fault, which is often disregarded when performing OCR grading for a conventional grid. In this paper, this selectivity problem of the OCR is discussed in depth through a comparative study of conventional grid and a modern IBDG dominated grid. The coordination time interval margin violations problems are demonstrated through theoretical calculations and real-time hardware-in-the-loop experiments. This research aims to provide better insights into the selectivity problem as a step towards achieving a cost-effective yet reliable overcurrent-based adaptive protection for IBDG dominated microgrid. [ABSTRACT FROM AUTHOR]

This paper presents a novel protection strategy for assuring power-system frequency stability. After many years of use, the existing (static) under-frequency load-shedding concept has proven to be reliable and fast. However, it does not adapt well to volatile operating conditions, which might often lead to a system collapse. This developed into a major obstacle, since operational conditions of modern power systems are persistently subjected to fast and unpredictable changes. Therefore, there is a need to introduce a new capability in under-frequency load-shedding that would be able to fine-tune the mismatch in active power in any conditions. From the practical aspect, a systematic implementation of improvements should not threaten system stability. In terms of cost, a minimum intervention in the existing concept is desirable. This is why we developed an effective upgrade of the existing concept by introducing a specialized group of intelligent electronic devices supported by a principal component analysis technique. This group should be operated alongside the existing solution to monitor the actual frequency conditions and to take over power-balancing when fine-tuning is required. This supports the existing load-shedding and improves the process of frequency stabilization. [ABSTRACT FROM AUTHOR]

This article presents a new adaptive and optimal overcurrent protection for large-scale wind farms using hybrid grey wolf optimizer and rule-based fuzzy logic controller (GWO-FLC) scheme. The proposed GWO-FLC based adaptive protection scheme overcomes the limitation of conventional protection scheme that suffers from maloperation of relays that damages the power components in the system during fault. Furthermore, due to the intermittent nature of wind, the generated current feeding the grid during extreme high and low wind speeds creates a significant difference in magnitudes of the generated current. Thus, the existence of only one group of settings for the overcurrent relays (OCRs) would cause drastic miscoordination and false tripping during fault. In order to test the performance of the proposed GWO-FLC scheme, several OCRs based on standard Schweitzer Engineering Laboratories industrial protection relay (SEL-751) are developed in MATLAB/Simulink. A large-scale wind farm model is also developed to perform fault analysis, relay setting, and coordination calculation. The GWO is implemented to attain optimal OCR coordination for the defined quadruple group settings for all relays, and the FLC is developed to provide adaptive feature for the relays so that the OCR group settings for each relay are intelligently updated according to the variation of wind speed. Finally, in a laboratory environment, the proposed protection scheme is implemented in real time using field-programmable gate array DE2-115 board equipped with Cyclone IV-E device (EP4CE115F29C7). It is found from both simulation and experimental results that the performance of the proposed hybrid GWO-FLC is robust, reliable, efficient and extremely satisfactory. [ABSTRACT FROM AUTHOR]

In active distribution networks, system reconfiguration and connection/disconnection of distributed generation (DG) can result in protection coordination failure of overcurrent relays. Determining one set of optimal relay settings that would satisfy all possible network topologies is either infeasible or results in high relay operating times. To address this problem, recently the concept of clustering the various network topologies into a limited set is proposed where an optimal Setting Group (SG) is determined for each network topology cluster. This article proposes a novel problem formulation that simultaneously obtains the optimal relay SG and network topology clusters. Due to the complexity and non-linearity of the SG protection coordination problem, the SG protection coordination problem is reformulated as a mixed-integer linear programming (MILP) problem. The effect of the relay characteristic type on reducing the operating times of relays is also investigated. Comparative analysis is provided that highlight the superior performance of MILP over other heuristic optimization techniques. Data exchange between circuit breakers, DGs, CPU and relays are developed based on the IEC 61850 standard to illustrate the implementation of the proposed adaptive protection scheme on real networks. [ABSTRACT FROM AUTHOR]

This article proposes a new adaptive commissioning methodology for arc flash mitigation in steel manufacturer users considering the Tap-to-Tap varying current consumption. This process is achieved through adaptative protection settings computed to reduce the total clearing time of relays adding the restriction of the incident energy. The proposed methodology carries out the detection of abrupt changes in current consumption to detect Tap-to-Tap change in operation stages of electric arc furnaces. The application of this methodology is performed on a steel manufacturer user and shows the reduction of the incident energy values according to Tap-to-Tap operation cycle. [ABSTRACT FROM AUTHOR]

The increasing proliferation of distributed generators (DGs) demands a robust and comprehensive design of the communication-based adaptive protection scheme, which must be able to not only deal with the known changes in the DGs-distribution system but also handle the unknown changes due to variations in the operating mode, network configuration, and number, type, and size of DGs. On one side, with the increasing installations of DGs, the deployment of the communication system in protection is increasing to monitor the system status and select the relays’ settings accordingly. However, on the other side, if information flow does not happen due to the presence of pre-fault failure of the relay-agents and/or communication links, a protection scheme may fail to provide the suitable protection. This paper proposes a centralized adaptive protection scheme to deal with such failures and varying operating conditions. It provides optimal relays settings for varying operating conditions of the DGs-distribution system with the aim of providing fast, comprehensive, and self-adaptive protection. In order to achieve these objectives, two algorithms have been developed: the first algorithm determines optimal hybrid pick-up settings of the relays, and the second algorithm determines the adaptive hierarchies of the relays. With the inclusion of these two algorithms, the relay coordination problem has been formalized linearly. The performance of the proposed scheme has been tested and validated for various known and unknown events with different types of short circuit faults of different fault impedances on the 37-bus IEEE test distribution system in a MATLAB simulation and coding environment. The results show that the proposed method not only provides the optimal relay's coordination in varying situations but also effectively reduces the protection latency due to pre-fault failures of the relays and communication links, and low level of fault currents. [ABSTRACT FROM AUTHOR]

This article proposes a new adaptive protection setting methodology for steel manufacturers, aiming to reduce miscoordination between main feeders and current consumptions due to fault clearance or high load disconnection. By detecting abrupt changes in current consumption, the computation of different protection settings may be achieved. The application of this methodology is performed through the assessment of a steel manufacturer who sustained an arc blast of one of their protection cells, and a description of the way in which the proposal permits avoidance of such catastrophic conditions. [ABSTRACT FROM AUTHOR]

Dynamically changing distribution system operating conditions compromises the coordination of the existing protection schemes. This paper proposes an online adaptive protection coordination scheme by utilizing numerical directional overcurrent relays (DOCRs) and commercial A Mathematical Programming Language (AMPL) based Interior Point OPTimization (IPOPT) solver. The proposed scheme also utilizes intelligent electronic devices and a communication channel to obtain real-time system information and to update relays settings. The presented approach is able to handle different operating conditions of the system, including loss of loads, generations, and lines. Further, the miscoordination arising due to injections of distributed generations (DGs) is also handled. The proposed approach has been tested on the IEEE 14-bus system (with and without DG), under various operating conditions. Overall system reliability enhancement using the proposed approach has been analyzed in terms of the amount of energy not supplied. Further, the optimum settings of DOCRs obtained using AMPL based IPOPT solver has been compared with those obtained by General Algebraic Modeling System based Sparse Nonlinear OPTimizer solver, OPTI Toolbox based IPOPT solver, MATLAB based interior point method, and metaheuristic genetic algorithm and differential evolution. It has been found that the proposed coordination approach gives good results in reasonably small time and thus, is suitable for the adaptive protection scheme. [ABSTRACT FROM AUTHOR]

This paper presents a centralized protection strategy for medium voltage dc microgrids. The proposed strategy consists of a communication-assisted fault detection method with a centralized protection coordinator and a fault isolation technique that provides an economic, fast, and selective protection by using the minimum number of dc circuit breakers. The proposed method is also supported by a backup protection that is activated if communication fails. This paper also introduces a centralized self-healing strategy that guarantees successful operation of zones that are separated from the main grid after the operation of the protection devices. Furthermore, to provide a more reliable protection, thresholds of the protection devices are adapted according to the operational modes of the microgrid and the status of distributed generators. The effectiveness of the proposed protection strategy is validated through real-time simulation studies based on the hardware in the loop approach. [ABSTRACT FROM AUTHOR]

This paper proposes an adaptive protection scheme for distribution systems with distributed generations (DGs). To mitigate the influences on the protection devices by DGs, an online calculation method of fault current under various system operation conditions is presented. By sampling local available measurements in the buses, a proposed optimized estimation method is used to calculate the Thevenin equivalent circuit parameters of the system dynamically. Moreover, the short-circuit current can be calculated accurately to set the overcurrent relay protection value considering the behavior of DGs during the fault. To ensure the accurate operation of the protection devices, a coordinated protection scheme, including primary and backup protection is presented. Performances of the proposed method and scheme have been verified by simulations on a sample distribution system based on PSCAD/EMTDC. The sensitivity and selectivity of the coordination between primary and backup protection are satisfied under different system operation conditions, fault locations, and types. [ABSTRACT FROM AUTHOR]

This paper presents a new approach in adaptive out-of-step (OOS) protection settings in power systems in real time. The proposed method uses extended equal area criterion (EEAC) to determine the critical clearing time and critical clearing angle of the system, which are vital information for the OOS protection setting calculation. The dynamic model parameters and the coherency groups of the system for EEAC analysis are determined in real time to ensure that the newly calculated settings suit with the prevalent system operating condition. The effectiveness of the method is demonstrated in simulated data from a 16-machine 68-bus system model. [ABSTRACT FROM PUBLISHER]

Communications network plays a key role in the next-generation microgrid protection schemes, as the protective relays need to communicate with each other to dynamically track their tripping currents due to the time-varying nature of the loads and the distributed generation (DG) outputs. Hence, communications cost and reliability are some of the key factors that need to be considered before deploying a microgrid protection scheme. In this paper, we introduce the concept of a hybrid microgrid protection system, which implements traditional differential protection scheme along with an adaptive microgrid protection scheme. While the differential scheme is more sensitive, yet relies on extensive communications, the adaptive scheme is less sensitive but has low communications load. The joint deployment of these two schemes has the potential to increase the accuracy and precision of the whole protection scheme, while reducing the overall communications cost. Moreover, we propose a preemptive switching algorithm for the microgrid relays, which ensures a seamless transition from differential protection to adaptive protection based on the bit error rate of the communications links. Some illustrative results are provided based on an IEEE 802.16/WiMAX network to justify the proposed hybrid protection scheme. [ABSTRACT FROM PUBLISHER]

Distribution networks are evolving toward the vision of smart grids, with increasing penetration of distributed generation (DG), introduction of active network management (ANM), and potentially islanded modes of operation. These changes affect fault levels and fault current paths and have been demonstrated to compromise the correct operation of the overcurrent protection system. This paper presents an adaptive overcurrent protection system which automatically amends the protection settings of all overcurrent relays in response to the impact of DG, ANM, and islanding operation. The scheme has been developed using commercially available protection devices, employs IEC61850-based communications, and has been demonstrated and tested using a hardware-in-the-loop laboratory facility. A systematic comparison of the performance of the proposed adaptive scheme alongside that of a conventional overcurrent scheme is presented. This comparison quantifies the decrease in false operations and the reduction of mean operating time that the adaptive system offers. [ABSTRACT FROM AUTHOR]

A significant increase in the penetration of distributed generation has resulted in a possibility of operating distribution systems with distributed generation in islanded mode. However, overcurrent protection of an islanded distribution system is still an issue due to the difference in fault current when the distribution system is connected to the grid and when it is islanded. This paper proposes the use of adaptive protection, using local information, to overcome the challenges of the overcurrent protection in distribution systems with distributed generation. The trip characteristics of the relays are updated by detecting operating states (grid connected or island) and the faulted section. The paper also proposes faulted section detection using time overcurrent characteristics of the protective relays. Simulation results show that the operating state and faulted section can be correctly identified and the protection system settings can be updated to clear the faults faster. [ABSTRACT FROM PUBLISHER]

This paper introduces a state-diagram-based protective algorithm for parallel circuit transmission lines using local information obtained at the relay bus. A new cross-differential technique is proposed which compares the currents in the corresponding phases of the parallel circuits in a 2-D space. A companion impedance-based algorithm is used to cover the evolving faults and some conditions in which the cross-differential technique is not able to discriminate the internal faults alone. The effect of the mutual coupling between parallel circuits on the measured impedances is adaptively compensated according to the status of the parallel circuit currents in the segmented 2-D space. The proposed state-diagram-based algorithm combines the outputs of the cross-differential and impedance-based techniques to provide a reliable response under all of the operating statuses of the parallel circuits. Extensive simulation studies using PSCAD/EMTDC software indicate that the proposed approach provides very reliable protection for the double-circuit transmission lines. It covers intercircuit and evolving faults, and is able to reliably select the faulted phases. [ABSTRACT FROM AUTHOR]

This paper shows two improvements related to the overcurrent functions (OCFs) for bus protection in distribution systems. The first topic is the use of two high-set definite-time OCF, in conjunction with the inverse-time OCF, for the main circuit breaker (MCB). A zone-interlocking signal can block one high-set definite-time OCF, while the other one is the fastest possible backup action. The second topic is the inclusion of a backup function at the MCB for cases of failure of a downstream relay, by using the OCF of this MCB to first trip the circuit breaker related to the corresponding downstream feeder. If the OCF of the MCB remains asserted, then this OCF trips the MCB after a suitable coordination time. Both improvements can be implemented by using the IEC-61850 standard. [ABSTRACT FROM AUTHOR]