Microgrids can be operated either grid-connected to reduce system losses and for peak shaving or islanded to increase reliability and provide backup power during utility outage. Such dual configuration capability imposes challenges on the design of the protection system. Fault current magnitudes will vary depending on the microgrid operating mode. In this paper, a microgrid protection scheme that relies on optimally sizing fault current limiters and optimally setting directional overcurrent relays is proposed. The protection scheme is optimally designed taking into account both modes of operation (grid-connected and islanded). The problem has been formulated as a constrained nonlinear programming problem and is solved using the genetic algorithm with the static penalty constraint-handling technique. The proposed approach is tested on two medium-voltage networks: a typical radial distribution system and on the IEEE 30-bus looped power distribution system equipped with directly connected conventional synchronous generators.

Optimal Protection Coordination for Microgrids With Grid-Connected and Islanded Capability

The time of operation of overcurrent relays (OCRs) can be reduced, and at the same time, the coordination can be maintained, by selecting the optimum values of time multiplier setting (TMS) and plug setting (PS) of OCRs This paper presents hybrid genetic algorithm (GA) - nonlinear programming (NLP) approach for determination of optimum values of TMS and PS of OCRs GA has a drawback of, sometimes, converging to the values which may not be optimum, and NLP methods have a drawback of converging to local optimum values, if the initial choice is nearer to local optimum This paper proposes a hybrid method to overcome the drawback of GA and NLP method, and determine the optimum settings of OCRs The main contributions of this paper are - 1) systematic method for formulation of problem of determining optimum values of TMS and PS of OCRs in power distribution network as a constrained nonlinear optimization problem, 2) determining initial values of TMS and PS using GA technique and finding final (global optimum) values using NLP method, thus making use of the advantages of both methods (and at the same time overcoming the drawbacks of the methods)

Optimum Coordination of Directional Overcurrent Relays Using the Hybrid GA-NLP Approach

Coordination of directional overcurrent relays in a multiloop subtransmission or distribution network is formulated as an optimization problem. In this paper, the coordination of directional overcurrent relays is formulated as a mixed-integer nonlinear programming problem and is then solved by a new seeker optimization technique. Based on the act of human searching, in the proposed seeker technique, the search direction and step length are determined in an adaptive way. The proposed method is implemented in three different test cases. The results are compared with previously proposed analytic and evolutionary approaches.

Coordination of Directional Overcurrent Relays Using Seeker Algorithm

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Power System Analysis And Design

Damage characterization of laminated composites has been thoroughly studied the last decades where researchers developed several damage models, and in combination with experimental evidence, contributed to better understanding of the structural behavior of these structures. Experimental techniques played an essential role on this progress and among the techniques that were utilized, acoustic emission (AE) was extensively used due to its advantages for in-situ damage monitoring with high sensitivity and its capability to inspect continuously a relatively large area. This paper presents a comprehensive review on the use of AE for damage characterization in laminated composites. The review is divided into two sections; the first section discusses the literature for damage diagnostics and it is presented in three subsections: damage initiation detection, damage type identification and damage localization, while the second section is devoted to damage prognostics and it focuses on the remaining useful life (RUL) and residual strength prediction of composite structures using AE data. In every section, efforts have been made to analyze the most relevant literature, discuss in a critical manner the results and conclusions, and identify possibilities for future work.

Damage characterization of laminated composites using acoustic emission: A review

A new comprehensive genetic algorithm method for optimal overcurrent relays coordination

This paper focuses on quantification of damage mechanisms in Standard Open-Hole Tensile (OHT) laminated composites using Acoustic Emission (AE) and Finite Element Method (FEM). To this aim, OHT tests were carried out in unidirectional glass/epoxy composite materials. AE accompanied with a wavelet and fuzzy C-means clustering methods were used to distinguish damage mechanisms of the specimen. These damages were consisted of three main mechanisms, including matrix cracking, fiber/matrix debonding and fiber breakage. FE analysis was utilized to validate the AE results. Scanning Electron Microscope (SEM) images were also used to investigate damage mechanisms in the specimen. The comparison of the applied methods shows that the difference in results of FE analysis and wavelet transform methods are less than 15 percent but there is a more difference (around 42 percent) between results of fuzzy C-means and FEM.

Correlation of acoustic emission with finite element predicted damages in open-hole tensile laminated composites

In interconnected networks, it is impossible to satisfy all coordination constraints. Some methods have been proposed in the literature to determine the minimum break point set (MBPS) before the coordination procedure. In this paper, a new method is presented which coordinates overcurrent relays and simultaneously determines minimum unsatisfied constraints as broken constraints (BCs). For the implementation of this method, a new objective function (OF) is defined that also includes constraints with various weightings. These weightings determine the priority of constraints for being satisfied which are obtained by means of some expert rules. The expert rules of previous papers are modified and weighted to determine the priority of constraints. The genetic algorithm is used to optimize the OF that has an internal feedback for determining the minimum BCs considering coordination criterion. The effectiveness of the proposed technique is demonstrated by comparing the results of two sample networks with those obtained by using the recently developed techniques.

Overcurrent Relays Coordination Considering the Priority of Constraints

In this paper an efficient method for optimal overcurrent relay coordination is proposed. In the proposed method using genetic algorithm, an objective function (OF) is developed to solve the problem of miscoordination for six pairs short circuit fault currents. The new OF is improved to be simple, optimal and efficient. This technique takes into account the changes in network configuration. The efficiency of the proposed technique is demonstrated by comparing the results of two different networks namely typical 8-bus & IEEE 30-bus systems with those obtained using the recently developed techniques. K e y w o r d s: coordination, genetic algorithm, overcurrent relays, protection, relay settings

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Optimal Relays Coordination Efficient Method in Interconnected Power Systems

Determination of the minimum break point set (MBPS) in interconnected networks is the key step during calculation and setting of overcurrent relays protection values. Recently, two separate approaches based on expert system and MBPS have been developed respectively. The first one considers the effects of fault level, network configuration, pilot protection and other protection systems. The second one defines protection relay dependency dimension (PRDD) for finding MBPS. By comparison of PRDD in a multi-loop network, the MBPS can be determined, and the process of comparison will not stop until the MBPS of the network is discovered. This paper introduces a new method which takes into account expert rules as well as MBPS simultaneously in the frame of the new objective function of genetic algorithm. It can also generate a new MBPS after each coordination process. The method is applied to the 8-buses and the IEEE 30-buses networks. The obtained results have revealed that the new method is accurate and capable of reducing miscoordinations.

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Reza Mohammadi

Papers

A new comprehensive genetic algorithm method for optimal overcurrent relays coordination

Correlation of acoustic emission with finite element predicted damages in open-hole tensile laminated composites

Overcurrent Relays Coordination Considering the Priority of Constraints

Optimal Relays Coordination Efficient Method in Interconnected Power Systems

Determination of the Minimum Break Point Set Using Expert System and Genetic Algorithm