The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
Walmir Freitas - One of the best experts on this subject based on the ideXlab platform.
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Power Imbalance application region method for distributed synchronous generator anti islanding protection design and evaluation
Electric Power Systems Research, 2011Co-Authors: Jose C M Vieira, Diogo Salles, Walmir FreitasAbstract:Abstract This paper presents a novel graphical approach to adjust and evaluate frequency-based relays employed in anti-islanding protection schemes of distributed synchronous generators, in order to meet the anti-islanding and abnormal frequency variation requirements, simultaneously. The proposed method defines a region in the Power mismatch space, inside which the relay non-detection zone should be located, if the above-mentioned requirements must be met. Such region is called Power Imbalance application region. Results show that this method can help protection engineers to adjust frequency-based relays to improve the anti-islanding capability and to minimize false operation occurrences, keeping the abnormal frequency variation utility requirements satisfied. Moreover, the proposed method can be employed to coordinate different types of frequency-based relays, aiming at improving overall performance of the distributed generator frequency protection scheme.
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characteristics of vector surge relays for distributed synchronous generator protection
Electric Power Systems Research, 2007Co-Authors: Walmir Freitas, Zhenyu Huang, Jose C M VieiraAbstract:This work presents a detailed investigation on the performance characteristics of vector surge relays used to detect islanding of distributed synchronous generators. A detection time versus active Power Imbalance curve is proposed to evaluate the relay performance. Computer simulations are used to obtain the performance curves. The concept of critical active Power Imbalance is introduced based on these curves. Main factors affecting the performance of the relays are analyzed. The factors investigated are voltage-dependent loads, load Power factor, inertia constant of the generator, generator excitation system control mode, feeder length and R/X ratio as well as multi-distributed generators. The results are a useful guideline to evaluate the effectiveness of anti-island schemes based on vector surge relays for distributed generation applications.
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Characteristics of voltage relays for embedded synchronous generators protection
IET Generation Transmission & Distribution, 2007Co-Authors: José Carlos M. Vieira, Walmir Freitas, Denis SallesAbstract:Here, a comprehensive characterisation of the performance of voltage relays, focusing on their capability to detect islanding of embedded synchronous generators is presented. Such characterisation is done by using the performance curves and the concept of critical reactive Power Imbalance, which allows a systematic analysis of voltage relays considering a wide range of system operating points. The impacts of important factors on the relay performance are evaluated, such as the presence of voltage-dependent loads and the generator exciter control mode. Moreover, a graphical approach that allows protection engineers to adjust voltage relays to reach two objectives simultaneously: (i) to be sensitive enough to detect islanding efficiently and (ii) to satisfy the protection requirements against abnormal voltage variation is proposed. Results can be quite attractive to understand voltage relays behaviour and limitations and thus, they can be adjusted more efficiently
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comparative analysis between rocof and vector surge relays for distributed generation applications
IEEE Transactions on Power Delivery, 2005Co-Authors: Walmir Freitas, C M Affonso, Zhenyu HuangAbstract:This paper presents a comprehensive comparative analysis between rate-of-change-of-frequency (ROCOF) and vector-surge (VS) relays for distributed generation islanding detection. The analysis is based on the concepts of detection-time versus active Power-Imbalance curves and critical active Power Imbalance. Such curves are obtained through dynamic simulations. The performance of these devices considering different scenarios is determined and compared. Factors such as voltage-dependent loads, generator inertia constant, and multidistributed generator systems are analyzed. False operation of these relays due to faults in adjacent feeders is also addressed. Results show that ROCOF relays are more reliable to detect islanding than vector surge relays when the active Power Imbalance in the islanded system is small. However, ROCOF relays are more susceptible to false operation than VS relays.
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performance of rocof relays for embedded generation applications
IEE Proceedings - Generation Transmission and Distribution, 2005Co-Authors: C M Affonso, Walmir Freitas, L C P Da SilvaAbstract:The performance characteristics of rate of change of frequency (ROCOF) relays for embedded generation islanding detection are investigated. The concepts of detection-time versus Power-Imbalance curve and critical Power Imbalance are proposed. These concepts are employed to determine the factors that may affect the islanding detection capability of ROCOF relays. The factors analysed are voltage-dependent loads, load Power factor, generator inertia constant, feeder length and X/R ratio and multi-embedded generators. In addition, false operation due to faults on adjacent feeders is investigated. The results show that ROCOF relays may become ineffective for islanding detection if the Power Imbalance in the islanded system is smaller than 15%. In addition, these devices have a high risk of false operation.
X Shi - One of the best experts on this subject based on the ideXlab platform.
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equilibrium analysis of supply chain structures under Power Imbalance
European Journal of Operational Research, 2011Co-Authors: N C P Edirisinghe, B Bichescu, X ShiAbstract:Abstract This paper investigates the implications of channel Power on supply chain stability in a setting where multiple suppliers sell substitutable products through a common retailer. Such supply chains have been traditionally analyzed as one- or two-stage Stackelberg non-cooperative games with all suppliers sharing balanced (equal) decision-making Power. In this paper, we relax this assumption and formulate game-theoretic models to examine scenarios where one supplier can act as the Stackelberg leader. Consequently, we analyze new supply chain structures and introduce the notion of structure dominance, a novel approach to analyze the performance of supply chains that has practical implications. Thus, a decision maker can employ the concepts of structure dominance to determine whether there exist supply chain scenarios that are more stable than others, i.e., less prone to Power reconfigurations, at both agent and group level. We find that Power Imbalance causes significant declines in supply chain profits, and the more balanced the agents are the higher their profits when demand is linear, regardless of product competition. It develops that neither the Manufacturer Stackelberg nor the Retailer Stackelberg supply chains are stable structures in our generalized setting, but that structures where Power is equally split between agents provide for best stability and performance.
Kimberly A Schonertreichl - One of the best experts on this subject based on the ideXlab platform.
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measuring 8 to 12 year old children s self report of Power Imbalance in relation to bullying development of the scale of perceived Power Imbalance
BMC Public Health, 2019Co-Authors: Helen J Nelson, Sharyn Burns, Garth E Kendall, Kimberly A Schonertreichl, Robert KaneAbstract:While Power Imbalance is now recognized as a key component of bullying, reliable and valid measurement instruments have yet to be developed. This research aimed to develop a self-report instrument that measures Power Imbalance as perceived by the victim of frequent aggressive behavior. A mixed methods approach was used (468 participants, Grade 4 to 6). This paper describes the exploratory (n = 111) and confirmatory factor analysis of the new instrument (n = 337), and assessment of reliablity and construct validity. A 2-factor model represented physical and social aspects of Power Imbalance (n = 127: normed chi-square = 1.2, RMSEA = .04, CF1 = .993). The social factor included constructs of group and peer valued characteristics. This research will enhance health and education professionals understanding of Power Imbalance in bullying and will inform the design and evaluation of interventions to address bullying in children.
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preadolescent children s perception of Power Imbalance in bullying a thematic analysis
PLOS ONE, 2019Co-Authors: Helen J Nelson, Sharyn Burns, Garth E Kendall, Kimberly A SchonertreichlAbstract:Bullying in schools is associated with an extensive public health burden. Bullying is intentional and goal oriented aggressive behavior in which the perpetrator exploits an Imbalance of Power to repeatedly dominate the victim. To differentiate bullying from aggressive behavior, assessment must include a valid measure of Power Imbalance as perceived by the victim. And yet, to date, there remains no agreement as to how to most accurately measure Power Imbalance among preadolescent children. This qualitative study explored children’s (age 9 to 11) understanding of Power Imbalance through thematic analysis of focus group discussions. Subthemes that emerged as influencing Power Imbalance include: age of victim, peer valued characteristics, and group membership and position. Subthemes of empathy and peer valued characteristics emerged as protecting against the negative impact of Power Imbalance.
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the factors that influence and protect against Power Imbalance in covert bullying among preadolescent children at school a thematic analysis
Journal of School Nursing, 2018Co-Authors: Helen J Nelson, Sharyn Burns, Garth E Kendall, Kimberly A SchonertreichlAbstract:In this article, the perceptions of preadolescent children (ages 9-11) regarding factors that influence and protect against Power Imbalance associated with covert aggression and bullying are explored. In aggression research, the term covert has been typically used to describe relational, indirect, and social acts of aggression that are hidden. These behaviors contrast with overt physical and verbal aggression. Children have previously conveyed their belief that covert aggression is harmful because adults do not see it even though children, themselves, are aware. We used focus groups to explore children's understanding of covert aggression and to identify children's experience and perception of adult support in relation to bullying. Thematic analysis supported the definition of covert aggression as that which is intentionally hidden from adults. Friendship, social exclusion, and secret from teacher were identified as factors that influence Power Imbalance, while support from friends and adult support protected against Power Imbalance.
Mollah Rezaul Alam - One of the best experts on this subject based on the ideXlab platform.
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assessing the performance of rocof relay for anti islanding protection of distributed generation under subcritical region of Power Imbalance
IEEE Transactions on Industry Applications, 2019Co-Authors: Mollah Rezaul Alam, Most Tasneem Ara Begum, Kashem M MuttaqiAbstract:In practice, the load-curve and distributed generation (DG) penetration level determines the Power Imbalance level that a network can experience if islanding occurs. Therefore, with the prior knowledge of load-curve and DG penetration level, the setpoint of rate-of-change-of-frequency (ROCOF) relays can be adjusted so as to make them suitable for a real network. This paper first investigates the subcritical Power Imbalance region of ROCOF relays through analytical formulation followed by extensive simulation study in order to establish the maximum boundary limit of ROCOF's nondetection zone (NDZ) under all possible deficit/excess of active and/or reactive Power Imbalance scenarios. Second, ROCOF's reliability (assessed by detection rate and false alarm rate) is expressed analytically and then, validated numerically by simulating a test network of Australia in MATLAB and OPAL-RT real-time digital simulation platform. Finally, ROCOF's performance is assessed through receiver operating characteristics curves and a detailed reliability study under variable setpoints and detection time of the relays; the assessment considers the number of islanding events associated with the time-wise percentage of Power Imbalance level computed from the net load demand and variable DG penetration in a real network. All these test results demonstrate a clear operational guideline for ROCOF relay.
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assessing the performance of rocof relay for anti islanding protection of distributed generation under subcritical region of Power Imbalance
IEEE Industry Applications Society Annual Meeting, 2018Co-Authors: Mollah Rezaul Alam, Most Tasneem Ara Begum, Kashem M MuttaqiAbstract:In practice, the load-curve and distributed generation (DG) penetration level determines the Power Imbalance level that a network can experience if islanding occurs. Therefore, with the prior knowledge of load-curve and DG penetration level, the operating point or setpoint of Rate-of-change-of-frequency (ROCOF) relays can be adjusted so as to make them suitable for a real network. To this end, this paper firstly investigates the subcritical Power Imbalance region of ROCOF relays through analytical formulation; then, simulation study is conducted under different load-types and at the existence of deficit/excess of active and/or reactive Power Imbalance scenarios in order to establish the maximum boundary limit of ROCOF under all scenarios. Secondly, employing reliability (assessed by Detection Rate and False Alarm Rate) and response time as key performance indicators, ROCOF's performance is evaluated using numerous islanding and nonislanding events simulated from a test network of Australia. Lastly, ROCOF's performance is assessed using the ROC (Receiver Operating Characteristics) curve along with relay setpoint; the assessment considers the number of islanding events associated with the time-wise percentage of Power Imbalance level (deficit/excess) calculated from the different DG penetration level and daily load-curve. All these test results demonstrate a clear guideline to select ROCOF's setpoint.
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Evaluating the effectiveness of a machine learning approach based on response time and reliability for islanding detection of distributed generation
IET Renewable Power Generation, 2017Co-Authors: Mollah Rezaul Alam, Kashem M Muttaqi, Abdesselam BouzerdoumAbstract:Conventional relays, such as vector surge relay, frequency relay and rate-of-change-of-frequency relay, are usually employed for islanding detection; however, these conventional relays fail to detect islanding incidents in the presence of small Power Imbalance inside the islanded system. This study presents an islanding detection approach for synchronous type distributed generation using multiple features extracted from network variables and a support vector machine (SVM) classifier. Features are extracted from a sliding temporal window, whose width is selected so as to achieve the highest detection rate at a fixed false alarm rate. The SVM classifier is trained with linear, polynomial and Gaussian radial basis function kernels, and the parameters of the kernels are tuned to improve the classification performance. The application of the proposed method is illustrated for islanding cases associated with different Power Imbalance conditions, including small Power Imbalance conditions associated with the non-detection zone of conventional relays. Furthermore, variation of detection time as a function of Power Imbalance scenarios, which involve all probable combinations of deficit of active/reactive and excess of active/reactive Power Imbalance, is assessed in the testing phase. The performance of the proposed approach is evaluated and compared with those of conventional relays in terms of reliability and response time of islanding detection.
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an approach for assessing the effectiveness of multiple feature based svm method for islanding detection of distributed generation
IEEE Transactions on Industry Applications, 2014Co-Authors: Mollah Rezaul Alam, Kashem M Muttaqi, Abdesselam BouzerdoumAbstract:Islanding detection is a critical protection issue, as conventional protection schemes such as vector surge (VS) and rate of change of frequency relays do not guarantee islanding detection for all network conditions. Integration of multiple distributed generation (DG) units of different sizes and technologies into distribution grids makes this issue even more critical. This paper presents a comprehensive analysis of the effectiveness of a new method for islanding detection in DG networks. The proposed method, which is based on multiple features and support vector machine (SVM) classification, has the potential to overcome the limitations of conventional protection schemes. The multifeature-based SVM technique utilizes a set of features generated from numerous set of offline dynamic events simulated under different network contingencies, operating conditions, and Power Imbalance levels. Parameters (such as voltage, frequency, and rotor angle) showing distinguishable variation during the formation of islanding are selected as features for classification of the events. Features associated with different islanding and nonislanding events are used to train the SVM. The trained SVM is tested on a typical distribution network containing multiple DG units. Simulation results indicate that the proposed method can work effectively with high degree of accuracy under different network contingencies and critical levels of Power Imbalance that may exist during islanding.
Kashem M Muttaqi - One of the best experts on this subject based on the ideXlab platform.
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assessing the performance of rocof relay for anti islanding protection of distributed generation under subcritical region of Power Imbalance
IEEE Transactions on Industry Applications, 2019Co-Authors: Mollah Rezaul Alam, Most Tasneem Ara Begum, Kashem M MuttaqiAbstract:In practice, the load-curve and distributed generation (DG) penetration level determines the Power Imbalance level that a network can experience if islanding occurs. Therefore, with the prior knowledge of load-curve and DG penetration level, the setpoint of rate-of-change-of-frequency (ROCOF) relays can be adjusted so as to make them suitable for a real network. This paper first investigates the subcritical Power Imbalance region of ROCOF relays through analytical formulation followed by extensive simulation study in order to establish the maximum boundary limit of ROCOF's nondetection zone (NDZ) under all possible deficit/excess of active and/or reactive Power Imbalance scenarios. Second, ROCOF's reliability (assessed by detection rate and false alarm rate) is expressed analytically and then, validated numerically by simulating a test network of Australia in MATLAB and OPAL-RT real-time digital simulation platform. Finally, ROCOF's performance is assessed through receiver operating characteristics curves and a detailed reliability study under variable setpoints and detection time of the relays; the assessment considers the number of islanding events associated with the time-wise percentage of Power Imbalance level computed from the net load demand and variable DG penetration in a real network. All these test results demonstrate a clear operational guideline for ROCOF relay.
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assessing the performance of rocof relay for anti islanding protection of distributed generation under subcritical region of Power Imbalance
IEEE Industry Applications Society Annual Meeting, 2018Co-Authors: Mollah Rezaul Alam, Most Tasneem Ara Begum, Kashem M MuttaqiAbstract:In practice, the load-curve and distributed generation (DG) penetration level determines the Power Imbalance level that a network can experience if islanding occurs. Therefore, with the prior knowledge of load-curve and DG penetration level, the operating point or setpoint of Rate-of-change-of-frequency (ROCOF) relays can be adjusted so as to make them suitable for a real network. To this end, this paper firstly investigates the subcritical Power Imbalance region of ROCOF relays through analytical formulation; then, simulation study is conducted under different load-types and at the existence of deficit/excess of active and/or reactive Power Imbalance scenarios in order to establish the maximum boundary limit of ROCOF under all scenarios. Secondly, employing reliability (assessed by Detection Rate and False Alarm Rate) and response time as key performance indicators, ROCOF's performance is evaluated using numerous islanding and nonislanding events simulated from a test network of Australia. Lastly, ROCOF's performance is assessed using the ROC (Receiver Operating Characteristics) curve along with relay setpoint; the assessment considers the number of islanding events associated with the time-wise percentage of Power Imbalance level (deficit/excess) calculated from the different DG penetration level and daily load-curve. All these test results demonstrate a clear guideline to select ROCOF's setpoint.
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Evaluating the effectiveness of a machine learning approach based on response time and reliability for islanding detection of distributed generation
IET Renewable Power Generation, 2017Co-Authors: Mollah Rezaul Alam, Kashem M Muttaqi, Abdesselam BouzerdoumAbstract:Conventional relays, such as vector surge relay, frequency relay and rate-of-change-of-frequency relay, are usually employed for islanding detection; however, these conventional relays fail to detect islanding incidents in the presence of small Power Imbalance inside the islanded system. This study presents an islanding detection approach for synchronous type distributed generation using multiple features extracted from network variables and a support vector machine (SVM) classifier. Features are extracted from a sliding temporal window, whose width is selected so as to achieve the highest detection rate at a fixed false alarm rate. The SVM classifier is trained with linear, polynomial and Gaussian radial basis function kernels, and the parameters of the kernels are tuned to improve the classification performance. The application of the proposed method is illustrated for islanding cases associated with different Power Imbalance conditions, including small Power Imbalance conditions associated with the non-detection zone of conventional relays. Furthermore, variation of detection time as a function of Power Imbalance scenarios, which involve all probable combinations of deficit of active/reactive and excess of active/reactive Power Imbalance, is assessed in the testing phase. The performance of the proposed approach is evaluated and compared with those of conventional relays in terms of reliability and response time of islanding detection.
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an approach for assessing the effectiveness of multiple feature based svm method for islanding detection of distributed generation
IEEE Transactions on Industry Applications, 2014Co-Authors: Mollah Rezaul Alam, Kashem M Muttaqi, Abdesselam BouzerdoumAbstract:Islanding detection is a critical protection issue, as conventional protection schemes such as vector surge (VS) and rate of change of frequency relays do not guarantee islanding detection for all network conditions. Integration of multiple distributed generation (DG) units of different sizes and technologies into distribution grids makes this issue even more critical. This paper presents a comprehensive analysis of the effectiveness of a new method for islanding detection in DG networks. The proposed method, which is based on multiple features and support vector machine (SVM) classification, has the potential to overcome the limitations of conventional protection schemes. The multifeature-based SVM technique utilizes a set of features generated from numerous set of offline dynamic events simulated under different network contingencies, operating conditions, and Power Imbalance levels. Parameters (such as voltage, frequency, and rotor angle) showing distinguishable variation during the formation of islanding are selected as features for classification of the events. Features associated with different islanding and nonislanding events are used to train the SVM. The trained SVM is tested on a typical distribution network containing multiple DG units. Simulation results indicate that the proposed method can work effectively with high degree of accuracy under different network contingencies and critical levels of Power Imbalance that may exist during islanding.