Protection Coordination of Distribution Network with Optimally Placed Distribution Generation

In recent years, distributed generation (DG) has become more common in modern distribution networks (DNs). The presence of these small-scale generation units within a DN brings new challenges to protection engineers, since short-circuit currents tend to increase; additionally, as with microgrids, modern DNs may feature several operational modes depending on their topology and the availability of DG. This paper presents a methodology for the optimal coordination of overcurrent relays (OCRs) in modern DNs with a high presence of DG. Given the fact that protection coordination is a non-linear and non-convex optimization problem, a hybrid harmony search and simulated annealing (HS-SA) approach was implemented for its solution and compared against other techniques, such as conventional HS, genetic algorithm (GA), particle swarm optimization (PSO) and hybrid PSO-HS. Several tests were performed on a DN, considering different operative scenarios as a function of the DG available within the network. A comparison with other works reported in the specialized literature was carried out, evidencing the applicability and effectiveness of the HS-SA technique in solving the optimal OCR coordination problem in modern DNs.

DC distribution systems are becoming more widespread in various fields like data centers, electric vehicle charging infrastructure, and microgrids because DC distribution systems offer lower power conversion losses compared to AC systems. In DC distribution systems, protection coordination among overcurrent relays (OCRs) is important for selectively isolating faults and ensuring system stability. However, integration of distributed generation (DG) in system, such as photovoltaic (PV), impacts the magnitude and rate of change of fault currents, which in turn can change relay operating characteristics and coordination time interval (CTI). In this paper, variations in fault current magnitude and change rate based on fault location and the point of common coupling (PCC) for distributed generation in DC distribution systems were analyzed and coordination time interval were also examined.

Emission of greenhouse gases and depletion of fossil fuel reserves are two key drivers, which are forcing the mankind to generate the future energy demand from the renewable energy resources. These resources are generally distributed in nature and are directly integrated at distribution levels. Increasing penetration of the distributed energy resources in distribution power networks creates additional operational and control issues. These are mostly regulatory, economical load dispatching, power quality and protection issues.Generally power distribution systems are protected with the help of dedicated over current based protection schemes. But increasing share of distributed energy resources penetration in electric utilities poses a serious threat to the existing protection coordination schemes of the distribution systems. Distributed energy resources connected distribution networks become interconnected in nature and protection coordination schemes, which are designed for unidirectional flow of fault currents become ineffective/non-functional.Therefore, new protection coordination schemes are required for providing the adequate protection coordination for distributed energy resources connected electric power networks. In the available literature, the protection coordination schemes for radial distribution systems and developments in the area of protection coordination are discussed in detail. A thorough review for all these protection coordination schemes for distribution systems with and without distributed energy resources is done in this review article. It includes the analytical and artificial intelligence based techniques application for coordination of protective relays in the distribution systems. The limitations and research gaps in the area of protection coordination schemes are also presented in this review article.The aim of this research paper is to bring all the available research in the area of relay coordination on one platform, so that it will help the emerging researcher to identify the future scope of relay coordination application for distributed energy resources connected distribution systems.

<abstract> <p>More and more distributed energy resources (DERs) are being added to the medium-voltage (MV) or low-voltage (LV) radial distribution networks (RDNs). These distributed power sources will cause the redistribution of power flow and fault current, bringing new challenges to the coordination of power system protection. An adaptive protection coordination strategy is proposed in this paper. It will trace the connectivity of the system structure to determine the set of relay numbers as a tracking path. According to the topology of the system structure, the tracking path can be divided into two categories: the main feeder path and the branch path. The time multiplier setting (TMS) of each relay can be used to evaluate the operation time of the over-current relay (OCR), and the operation time of the relay can be used to evaluate the fitness of the TMS setting combination. Furthermore, the relay protection coordination problem can be modeled to minimize the accumulated summation of all primary and backup relay operation time (OT) subject to the coordination time interval (CTI) limitation. A modified particle swarm optimization (MPSO) algorithm with adaptive self-cognition and society operation scheme (ASSOS) was proposed and utilized to determine TMS for each relay on the tracking path. A 16-bus test MV system with distributed generators (DGs) will be applied to test the adaptive protection coordination approach proposed in this paper. The results show that the proposed MPSO algorithm reduces the overall OT and relieves the impact on protection coordination settings after DG joins the system. The paper also tests and compares the proposed MPSO with other metaheuristic intelligence-based random search algorithms to prove that MPSO possesses with increased efficiency and performance.</p> </abstract>

Directional over current relays (DOCRs) have been in use for ensuring the complete protection of the power system network. However, the modern power system is getting complex with the increased penetration of Renewable Energy Source (RES) based distributed generators (DGs), as the current flow become bidirectional. Hence, the system demands faster operation of the protection devices to prevent any major outages. Optimal values of all the DOCR settings viz, TDS and Ip need to be found out such as to minimize the overall time of operation of all the relays in the network. This study focuses on the comparative study of the optimization problem carried out using the prominent optimization algorithms – Particle Swarm Optimization (PSO), Henry Gas Solubility Optimization (HGSO) and Differential Evolution (DE). The ability of techniques is established on IEEE 6 – bus & WSCC 9 – bus test systems for mid-point line faults. The Protection Coordination Problem (PCP) is formulated as non-linear programming (NLP) problem, and the optimal settings of the relays TDS and Ip are achieved using MATLAB R2021a platform and validated the results in POWER WORLD simulator software. The results depict that the HGSO method shows a significant reduction in relays' time of operation compared to PSO, but DE gives superior results compared to other techniques with a minimum computational time.

The model of directional over current relays (DOCRs) coordination is considered as an optimization problem. It is generally formulated as linear programming (LP), non-linear programming (NLP) and mixed integer non-linear programming (MINLP), according to the nature of the design variables. For each kind of formulation, the main goal is to minimize the summation of operating times of primary relays, by setting optimal values for decision variables as time dial setting (TDS) and pickup current setting (IP) or plug setting (PS). In this paper, we proposed an oppositional Jaya (OJaya) algorithm with distance-adaptive coefficient (DAC), to effectively solve the DOCRs coordination problem. Firstly, by oppositional learning (OL), the searching space of Jaya is expanded and the diversity of its population is strengthened; secondly, by DAC, the population's trends of running towards the best position and escaping from the worst position is accelerated. The performance of OJaya is evaluated by 3-bus, 8-bus, 9-bus and 15-bus testing systems, in aspects of convergence rate, objective function value, robustness and computation efficiency. The results indicate the effectiveness and superiority of OJaya in solving DOCRs coordination problems compared with standard Jaya.

In this paper, the effect of using user defined characteristics relay on the sizing of fault current limiters (FCLs) are investigated. FCL is implemented in series with utility to tackle protection issues in looped networks due to incorporation of distributed generation (DG) in distribution systems. A protection coordination strategy is applied through employing user-defined characteristics which classifies directional overcurrent’ constants for relay characteristics (A) and for the inverse time type (B) as adjustable setting variables in addition to conventional setting variables; pick-up current (IP) and time multiplier setting (TDS). The four relay settings are picked up optimally along with optimum value of FCL. The problem is formulated as a constrained non-linear programming (NLP) problem with main objective of minimizing overall operating time of relays. The proposed approach is tested on meshed power distribution network of IEEE 30-bus. Results achieved by the proposed strategy show a reduction in overall relay operating time and the minimum value of FCL.

The aim of the relay coordination is that protection systems detect and isolate the faulted part as fast and selective as possible. On the other hand, in order to reduce the fault clearing time, distance protection relays are usually equipped with pilot protection schemes. Such schemes can be considered in the Distance and Directional Over-Current Relays (D&DOCRs) coordination to achieve faster protection systems, while the selectivity is maintained. Therefore, in this paper, a new formulation is presented for the relay coordination problem considering pilot protection. In the proposed formulation, the selectivity constraints for the primary distance and backup overcurrent relays are defined based on the fault at the end of the transmission lines, rather than those at the end of the first zone of the primary distance relay. To solve this nonlinear optimization problem, a combination of Genetic Algorithm (GA) and Linear Programming (LP) is used as a Hybrid Genetic Algorithm (HGA). The proposed approach is tested on an 8-bus, the IEEE 14-bus and the IEEE 39-bus test systems. Simulation results indicate that considering the pilot protection in the D&DOCRS coordination, not only obtains feasible and effective solutions for the relay settings, but also reduces the overall operating time of the protection system.

Distributed generation (DG) significantly improves power system reliability and voltage profile, and reduces power losses. These benefits can be maximized by optimizing the DG utilization, which greatly depends on adequate number, size, and placement of DG. This study proposes a high-convergence optimization technique for optimal DG placement in distribution networks, aiming to reduce power losses and improve voltage profile and voltage stability index. The technique is tested on a 7-bus system before being verified on the IEEE 33-bus system. After validation, it is tested on a 71-bus distribution network (DN). The estimated ideal size for a single DG is used as a limit for determining the optimal placement and size of multiple DG units. The results show that there is a loss reduction of 70.09%, 61.43%, and 71.15% for the 7-bus, IEEE 33-bus, and 71-bus systems, respectively, from their base case loss. The average absolute error of voltage of the aforementioned buses also shows similar enhancement, decreasing from 0.0144, 0.0561, and 0.0527, to 0.0058, 0.0209, and 0.0184, respectively. The voltage stability index of each DN has increased significantly in comparison to the base case. The comparison demonstrates that the proposed technique can provide better results for any size of distribution network.

Introduction of distributed generation (DG) to the power system may lead to nonselective protection actions. For every future DG installation, the relay settings need to be modified to guarantee protection coordination that can lead to numerous changes in relay settings. This paper presents a novel approach to plan relay protection coordination considering future DG installations. Thus, this paper aims at proposing a method capable of optimally identifying one set of relay settings valid for all possible future DG planning scenarios. The proposed algorithm is formulated as a linear programming problem and the simplex algorithm is utilized to solve it. The proposed approach is tested on the distribution part of the modified meshed IEEE 14-bus system and the IEEE 13-bus radial test system. Comparative studies have been conducted to highlight the advantages of the proposed approach under various planning scenarios considering application of fault current limiters.

High penetration level of distributed generation (DG) leads to improper protection coordination of the distribution system. In this paper, multiple DG locations are considered to evaluate the protection coordination index value. Due to the penetration of DG causes the change in fault current levels. So to prevent relay maloperation, change in co-ordination of relays is required. Further fault current limiters are used to enhance protection coordination index. Fault currents reduced within the breaking capacity of protective devices when FCL is introduced into the system in the presence of DG penetration. IEEE-14 bus test system is considered in the analysis. A mixed integer PSO Algorithm is used to enhance PCI index and to find optimal FCL size.

The effective coordination of directional overcurrent relays (DOCRs) is essential for maintaining the stability and dependability of power systems. This work presents a modified grey wolf optimization (MGWO) approach for addressing the DOCR coordination problem. The MGWO algorithm improves the original grey wolf optimization (GWO) by increasing convergence characteristics and balancing the exploration and exploitation stages. This equilibrium is attained by a dimension learning-hunting method and a quadratic reduction in the control parameter during the optimization phase. DOCR coordination is optimized using the MGWO method, using decision factors such as pickup current, time dial setting, and curve type. The goal is to reduce the total working time of primary relays while maintaining selectivity and shortening the discrimination time between primary and backup relays. The suggested MGWO technique is evaluated on the IEEE 8 bus system with two scenarios and compared to other optimization approaches. The results reveal that MGWO outperforms previous algorithms, achieving improvements in the objective function ranging from 5.52% to 58.19%. Additionally, the DOCR settings created by MGWO are evaluated using ETAP software to assure compliance with operational requirements and prevent violations of DOCR coordination.Keywords: Directional Overcurrent Relay Coordination, Grey Wolf Optimization, Multiple Curves, Pickup Current, Time Dial Setting.

Distributed generation (DG) is commonly used to supply the local loads. The penetration of distributed generation leads to violating the relay coordination in the distribution network. The interconnection of DG affects miscoordination of distribution system protection, because of the generator ability to contribute large fault currents to the fault point. The impact of DG on relay coordination affect the operating time of relay. The CTI associated with primary and backup relay pairs is getting violated due to changes in fault current level. Thus, coordination between primary and backup relays fails in the presence of distributed Generation. Hence, the interconnection of DG in the distribution system causes an adverse impact on protection coordination. Relay coordination problem has many constraints due to coordination criteria. Heuristic based optimization techniques are used to solve the optimization problems. These techniques have a drawback of converging to the values that may not be optimum due to the wide range of design variables and difficulty in getting an initial feasible solution with a short range of design variables. This paper presents a new algorithm to overcome the problem of the initial feasible solution in determining the optimum settings of OCRs. In this context, the optimization problem is formulated as constrained non-linear optimization problem and is determining using Genetic Algorithm (GA). This algorithm is tested on two different networks that found suitable to give satisfactory results.

Due to the concerns for reduction of system losses, providing back-up power during loss of the grid, mitigation of energy security risks and conspicuous perturbation of power outages triggered by severe environmental constraints; the modernized distribution grids elicited grid resiliency and reliability enhancement through pragmatic enforcement of the Microgrid (MG) concept with distributed generation. With the proliferating power ultimatum, several intricate factors prone to MG operation modes, bidirectional power flow complexities, management and control of power transfer, varying fault current contribution, and high impedance faults (HIF) customized the network configuration and imperiled the protection system operation and system stability. The propitious utility framework persuaded the prerequisites to embrace the integration of state-of-the-art affiliated Distributed Energy Resources (DERs), which requires assimilated and coordinated studies to emphasize the outcomes of an efficient, reliable, and fast protection scheme for both the grid-connected and islanded modes of operation. Operating modes of distributed generation (DG) will affect the magnitude and direction of fault currents resulting in failure of protection coordination between directional overcurrent relays (DOCRs). In this paper, the negative-sequence based adaptive directional overcurrent relay (NSADOCR) stratagem is proposed. Protection coordination is accomplished by a new adaptive approach, which alters time dial setting (TDS) of negative-sequence overcurrent relay based on the ratio of the normal mode to operating mode of plug setting multiplier function. Furthermore, the direction of fault is attained using phase change in between the pre-fault and superimposed negative-sequence current components. Performance of the NSADOCR is evaluated on the dSPACE controller board, which is interfaced with Real- Time Digital Simulator (RTDSTM) to perform the hardware-in-the-loop (HIL) tests. Extensive simulation studies and hardware results on DG systems exemplify and indicate that the new adaptive technique results in effective protection coordination over the conventional approach, considering various distribution network (DN) modes of operation.

<p>Protective relays coordination is the process of determining the exact relay settings such that the relay closes to the fault would operates faster than other relays. The operating time of each relay depends on two independent variables called Pickup current (Ip) and Time Dial Setting (TDS). In this paper, a PSO algorithm has been presented to determine the coordination of Directional Over-Current Relays (DOCRs) in presence of multi-system FACTS devises. From the simulation result and analysis, the impact of TCSC location in the in 33-bus distribution system on Directional Over-Current Relays has been observed on the optimal relays settings as well as the effectiveness of the proposed algorithm in finding optimal coordination of directional over-current relays.</p>