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

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Operations research: applications and algorithms / Wayne L. Winston

The authors would like to sincerely thank T. Aghdam et al. for their thoughtful discussion on our paper. They raise a valid, important and excellent point where the backup scheme of dual setting relays will not be fully coordinated properly. As such, one will experience, as stated by the discussers, for a fault at F1, R5 forward operation operating before R3 reverse operation. As suggested by the discussers, a possible solution would be to add (2) and this would yield both dual setting and conventional relay results the same and thus no improvement in operating times can be achieved by utilizing dual setting relays. The issue of possible loss of selecitivity but for definite time relays was reported in [1] and to resolve this issue, a communication link was used to block the operation of upstream relays [1] . This same approach can be applied to the dual settings relays and thus, another solution to resolve the dual setting selectivity problem would be to utilize a low bandwidth communication between relays which can then realize the full advantages of dual setting relays. The reported results in the paper can be achieved with proper protection coordination by amending dual setting relays with a low bandwidth communication that is utilized such that R1, once it detects an increase in current, would send a signal to block the unwanted operation of forward operating relays that are affected by that fault (for example, for a fault at F1, R1 forward operation sends a signal to block R5 forward operation and R5 forward operation sends a signal to block the forward operation of R4). This would apply to all relays in the system. Once again, we thank the reviewers for their careful review of the paper.

Closure to “Optimal Protection Coordination for Meshed Distribution Systems With DG Using Dual Setting Directional Over-Current Relays”

Distribution systems are continuously exposed to fault occurrences due to various reasons, such as lightning strike, failure of power system components due to aging of equipment and human errors. These phenomena affect the system reliability and results in expensive repairs, lost of productivity and power loss to customers. Since fault is unpredictable, a fast fault location and isolation is required to minimize the impact of fault in distribution systems. Therefore, many methods have been developed since the past to locate and detect faults in distribution systems with distributed generation. The methods can be divided into two categories, conventional and artificial intelligence techniques. Conventional techniques include travelling wave method and impedance based method while artificial intelligence techniques include Artificial Neural Network (ANN), Support Vector Machine (SVM), Fuzzy Logic, Genetic Algorithm (GA) and matching approach. However, fault location using intelligent methods are challenging since they require training data for processing and are time consuming. In this paper, most of the techniques that have been developed since the past and commonly used to locate and detect faults in distribution systems with distributed generation are reviewed. Research works in fault location area, the working principles, advantages and disadvantages of past works related to each fault location technique are highlighted in this paper. Hence, from this review, the opportunities in fault location research area in power distribution system can be explored further.

Fault location and detection techniques in power distribution systems with distributed generation: A review

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.

Optimal Coordination of Directional Overcurrent Relays Using a New Time–Current–Voltage Characteristic

Overcurrent relays (OCR) are the major protection devices in a distribution system. To reduce the power outages, mal-operation of the backup relays should be avoided, and therefore, OCR time coordination in power distribution network is a major concern of protection engineer. The OCR time coordination in ring fed distribution networks is a highly constrained optimization problem. The purpose is to find an optimum relay setting to minimize the time of operation of relays and at the same time, to avoid the mal-operation of relays. This paper presents continuous genetic algorithm (CGA) technique for optimum coordination of OCR in a ring fed distribution system. Constraints are incorporated in the fitness function making use of the penalty method. The CGA is inherently faster than binary genetic algorithm (GA) because the chromosomes do not have to be decoded. Also the CGA gives an advantage of requiring less storage than binary GA.

Optimum coordination of overcurrent relay timing using continuous genetic algorithm

This paper presents genetic algorithm (GA) method for coordination of overcurrent (OC) relays. The OC relays are the major protection devices in a distribution system. OC relay is usually employed as backup protection. But in some situations it may be the only protection provided. To reduce the power outages, mal-operation of the backup relays should be avoided, and therefore, OC relay coordination in power distribution network is a major concern of protection engineer. The OC relay coordination in ring fed distribution networks is a highly constrained optimization problem. The purpose is to find an optimum relay setting to minimize the time of operation of relays and at the same time, to avoid the mal-operation of relays. This paper presents GA technique for optimum coordination of OC relays in a ring fed distribution system. Constraints are incorporated in the fitness function making use of the penalty method. Computer programs (using MATLAB) have been developed for optimum coordination of OC relays using GA technique.

Optimum coordination of overcurrent relays in distribution system using genetic algorithm

This article presents the simplex method for optimum time coordination of directional overcurrent relays. The main contribution of this article is the application of the simplex method in spite of the inherent unsuitability of the problem. This is achieved by applying the simplex algorithm to the dual of the problem. Furthermore, there are reductions in the number of calculations and memory requirement, as the artificial variables need not be introduced. A comparison with other variants of the simplex algorithm and the genetic algorithm is also presented. It has been shown that the proposed method is applicable for finding the optimum coordination, even when a variety of overcurrent relays is present in the system.

Optimum Coordination of Overcurrent Relay Timing Using Simplex Method

This paper presents dual simplex method for coordination of overcurrent (OC) relays. The OC relays are the major protection devices in a distribution system. OC relay is usually employed as backup protection. But in some situations it may be the only protection provided. To reduce the power outages, mal-operation of the backup relays should be avoided, and therefore, OC relay coordination in power distribution network is a major concern of protection engineer. The OC relay coordination in ring fed distribution networks is a highly constrained optimization problem. The purpose is to find an optimum relay setting to minimize the time of operation of relays and at the same time, to avoid the mal-operation of relays. This paper presents dual simplex technique for optimum coordination of OC relays in a ring fed distribution system. A brief comparison with two phase simplex method is also given.

Prashant P. Bedekar

Papers

Optimum coordination of overcurrent relay timing using continuous genetic algorithm

Optimum coordination of overcurrent relays in distribution system using genetic algorithm

Optimum Coordination of Overcurrent Relay Timing Using Simplex Method

Optimum Coordination of Overcurrent Relays in Distribution System Using Dual Simplex Method

Fault section estimation in power system using Hebb's rule and continuous genetic algorithm