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

Development of an Optimal Coordination Scheme For Dual Relay Setting In Distribution Network Using Smell Agent Optimization Algorithm

This research work is aimed at developing an optimal coordination scheme for dual relay settings in distribution system. The fault current through a relay in forward direction is usually higher than that in the reverse direction for distribution system. Therefore, it is preferable to have a dual setting directional over-current relay. These relays have the capability to operate in both directions (forward and reverse direction) of fault current with two independent relay settings. Additional fault current contribution to the fault location is present due to the integration of distributed generation to the system. The coordination problem is therefore formulated as a nonlinear optimization problem to help mitigate the operating times of the relays using smell agent optimization (SAO) technique. The developed model was applied on IEEE 14-bus network equipped with synchronous distributed generation. The protection setting comprises of two time dial settings (TDS) and a pick up current setting for each relay. The SAO was used to obtain the TDS with the sole purpose of minimizing it while ensuring that the constraints set were satisfied. In the case of TDS with three cases of faults considered. the results obtained showed that the maximum fault current in all the three cases represent 6.79% while the minimum fault current was reduced to 2.70% when compared with the base case. The developed technique thereby achieved a reduction of time dial settings for which the relay operation of 14.50% and 13.69% reduction for the adopted 14 bus IEEE network

Impact of distributed generation on protection and voltage regulation of distribution systems : a review

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.fi=vertaisarvioitu|en=peerReviewed

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

The power system and microgrid protection-a review

In recent years, power grid infrastructures have been changing from a centralized power generation model to a paradigm where the generation capability is spread over an increasing number of small power stations relying on renewable energy sources. A microgrid is a local network including renewable and non-renewable energy sources as well as distributed loads. Microgrids can be operated in both grid-connected and islanded modes to fill the gap between the significant increase in demand and storage of electricity and transmission issues. Power electronics play an important role in microgrids due to the penetration of renewable energy sources. While microgrids have many benefits for power systems, they cause many challenges, especially in protection systems. This paper presents a comprehensive review of protection systems with the penetration of microgrids in the distribution network. The expansion of a microgrid affects the coordination and protection by a change in the current direction in the distribution network. Various solutions have been suggested in the literature to resolve the microgrid protection issues. The conventional coordination of the protection system is based on the time delays between relays as the primary and backup protection. The system protection scheme has to be changed in the presence of a microgrid, so several protection schemes have been proposed to improve the protection system. Microgrids are classified into different types based on the DC/AC system, communication infrastructure, rotating synchronous machine or inverter-based distributed generation (DG), etc. Finally, we discuss the trend of future protection schemes and compare the conventional power systems

Inter-trip links incorporated optimal protection coordination

Due to advances in smart grid, different communication links as delay, inter-trip and activation are used between relays to enhance the protection system performance. In this paper, the effect of inter-trip links on optimal coordination of directional overcurrent relays (DOCRs) is analytically investigated and modelled. Moreover, an index is proposed to find the optimum locations for inter-trip link installation to reach the minimal fault clearance times under the selectivity constraint. Then a method is proposed to determine the candidate locations of inter-trip links and the associated reduced operating times. An Exhaustive search approach is also used to validate the efficiency of the proposed method. The method is simulated and tested on distribution network of IEEE 33 bus using the Power Factory software and MATLAB optimization toolbox. Genetic algorithm is used as an optimization tool to find optimal settings of relays. The results indicate the capability of proposed method in optimal protection coordination with optimum inter-trips

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

DWT-Differential Analysis Optimization technique Used in the protection of Microgrid

This paper process DWT-differential analysis for optimal relay coordination issue for the microgrid. This solution works for grid-connected as well as the disconnected mode of operation. Coordination among relays of the microgrid is a complex part to handle, as the insertion of DG causes a bidirectional flow of current. Advanced protection methods involving DWT analysis of fault current can provide intelligent and smart ways of protection. Previous work has been applied with the differential algorithm on grid-connected and islanded mode, but one major deficiency is an increase in operating time of primary and secondary relay, which further decreases the reliability of Microgrid. The proposed system relies on DWT-differential Analysis based approach, which removes all unwanted noise and bandwidth from fault signal and differential analysis helps to select the best pair of a relay. The problem is formulated as a Non-linear programming constraint to minimize overall operating Relay time. The Scheme is tested with IEEE-9 bus system. The comparative analysis is carried out with two traditional methods, the result shows that it achieves a remarkable reduction in operating time in the primary and backup relay