Online ISSN
1751-8695
Print ISSN
1751-8687
IET Generation, Transmission & Distribution
Volume 6, Issue 10, October 2012
Volumes & issues:
Volume 6, Issue 10
October 2012
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- Author(s): M.M. Eissa
- Source: IET Generation, Transmission & Distribution, Volume 6, Issue 10, p. 931 –939
- DOI: 10.1049/iet-gtd.2011.0839
- Type: Article
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The proposed technique is based on extracting the windowed wavelet transform of fault generated transients to distinguish between faults in a busbar protection zone from those outside the zone, particularly in case of early and severe current transformer (CT) saturation. Most given techniques are tending to block the differential measurement during the portion of the cycle that a current transformer is saturated. Some other techniques bring more meaning to the breakpoint settings of the operating characteristic. The traditional differential concept is based on the current magnitude for estimating the restraining and biasing values. The significant imbalance comes from the secondary current of a current transformer with a resistive burden which collapses to zero when saturation occurs and it remains at zero until the time when the next zero crossing would have occurred. The study describes a new technique with improved characteristic and the differential concept does not depend on the current magnitude. The wavelet transform (WT) depends on high frequencies of the faulted signal produced owing to CT saturation. The proposed WT is based on Mexican basis function that was found to be an excellent discriminant for identifying the fault signals during the CT saturation. The time and frequency information during saturation are obtained rather than the current magnitude. - Author(s): A. Ashrafian ; M. Rostami ; G.B. Gharehpetian
- Source: IET Generation, Transmission & Distribution, Volume 6, Issue 10, p. 940 –950
- DOI: 10.1049/iet-gtd.2012.0047
- Type: Article
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In this study, a hyperbolic S-transform-based method is proposed to discriminate most important transient fault currents of transformers. First, the proposed method discriminates external faults from other disturbances. Then, the S-transform is applied to differential currents. An index is suggested by using absolute deviations of the S-matrix of differential currents to discriminate internal incipient faults in addition to inrush currents and internal faults. The relay issues an alarm signal in the case of the incipient fault but restrains during the magnetising inrush current. If an internal fault is recognised, the relay will issue a trip signal. To study the robustness of the suggested method, a program is developed in the MATLAB environment. The inputs of this program are differential current signals, derived from a system modelled by EMTP software. In order to simulate the internal incipient fault along with internal turn to turn and turn to earth faults, the transformer is modelled as 8×8 RL matrices, derived by using subroutine BCTRAN in EMTP. Also, differential currents are contaminated by noise and it is shown that the suggested method is not affected by noise and it can discriminate incipient faults, inrush currents, internal faults and external faults. - Author(s): A. Beroual ; M.L. Coulibaly ; O. Aitken ; A. Girodet
- Source: IET Generation, Transmission & Distribution, Volume 6, Issue 10, p. 951 –957
- DOI: 10.1049/iet-gtd.2012.0057
- Type: Article
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This study is devoted to the optical and electrical characterisation of discharges propagating over insulators made of polytetrafluoroethylene (PTFE) filled with different kinds of micro-mineral fillers immersed in gas or gaseous mixture, under lightning impulse voltage (1.2/50 µs), using a point-plane electrode arrangement. The fillers the authors investigated are MoS2, Al2CoO4, SiO2 and CaF2. The gases and mixture the authors considered are SF6, CO2 and SF6-CO2. It is shown that the stopping length of discharges Lf increases quasi-linearly with the voltage; Lf is shorter in SF6 than in CO2 and it is higher when the point electrode is positive than when it is negative while the initiation voltage of discharges is higher with a negative point than with a positive one. The discharges do not always present a radial structure as reported in the literature. Also, the type of filler greatly influences the characteristics of creeping discharges. In a given gas or mixture, the shortest Lf is obtained with PTFE filled with MoS2 or Al2CoO4. Thus, insulators with these fillers appear as the best insulators. - Author(s): P.K. Tiwari and Y.R. Sood
- Source: IET Generation, Transmission & Distribution, Volume 6, Issue 10, p. 958 –967
- DOI: 10.1049/iet-gtd.2011.0722
- Type: Article
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958
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This study presents an efficient approach to optimal allocation of unified power flow controller (UPFC) in a pool and bilateral power market. The optimisation technique has been used with an objective to maximising social welfare (SW) by suitable location, number and rating of the UPFC in power system working under a deregulated environment. The proposed method accurately evaluates SW by determining locational marginal pricing based on the marginal cost theory. The impact of the UPFC on system real power losses has also been investigated. The effectiveness of the proposed optimal technique has been tested on the 39-bus New England system with addition of four bilateral transactions. - Author(s): H. Erişti and Y. Demir
- Source: IET Generation, Transmission & Distribution, Volume 6, Issue 10, p. 968 –976
- DOI: 10.1049/iet-gtd.2011.0733
- Type: Article
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In this study, a new approach for the classification of power quality events is presented. Also, power quality disturbances, which occur in each phase of the power system after a fault event, are classified with the proposed system. In the proposed recognition system, three-phase voltage signals are used in order to identify the type of power quality events. Three-phase voltage signals are subjected to normalisation and segmentation processes. A wavelet transform method is used in order to obtain the distinctive features of event signals. An efficient feature vector, which represents the distinctive characteristics of three-phase event voltage signals and reduces data size, is extracted by applying the two-stage feature extraction process. Power quality event types are determined by using a support vector machine classifier. At the last stage of intelligent recognition system, types of power quality disturbances regarding each fault event are identified by doing a further analysis. Real power system data are used to evaluate the performance of the proposed approach. According to the obtained results, proposed intelligent recognition system classifies power quality event types with a high accuracy. The analyses and results also show that the proposed approach is efficient, reliable and applicable. - Author(s): D. Hazarika
- Source: IET Generation, Transmission & Distribution, Volume 6, Issue 10, p. 977 –985
- DOI: 10.1049/iet-gtd.2011.0786
- Type: Article
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The study presents a new method for monitoring the voltage stability condition of a bus using measurements of the bus variables. For this purpose, bus real power, bus reactive power and bus voltage of a target/selected bus have to be measured (sampled) for two consecutive time frames. These measured values are used to monitor the voltage stability condition of a bus using the mathematical basis developed in this study. The validity and applicability of the proposed method has been established through simulation on IEEE 30 and IEEE 118 bus system. - Author(s): F. Shahnia ; M.T. Wishart ; A. Ghosh ; G. Ledwich ; F. Zare
- Source: IET Generation, Transmission & Distribution, Volume 6, Issue 10, p. 986 –1000
- DOI: 10.1049/iet-gtd.2011.0781
- Type: Article
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A novel intelligent online demand side management system is proposed for peak load management in low-voltage distribution networks. This method uses low-cost controllers with low-bandwidth two-way communication installed in custumers’ premises and at distribution transformers to manage the peak load while maximising customer satisfaction. A multi-objective decision making process is proposed to select the load(s) to be delayed or controlled. The efficacy of the proposed control system is verified by simulation of three different feeder types. - Author(s): X. Han ; J. Guo ; P. Wang
- Source: IET Generation, Transmission & Distribution, Volume 6, Issue 10, p. 1001 –1008
- DOI: 10.1049/iet-gtd.2011.0704
- Type: Article
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When wind passes over a hilly land, the complex terrain feature will observably change wind speed. Wind speed distribution on a hill is much different from that on a flat area. The wake produced by an upstream wind turbine generator (WTG) may affect power output of a downstream WTG. When a WTG fails, wind speed distribution over a wind farm also changes, which leads to different wind power output. This study proposes a time sequential Monte Carlo simulation technique to evaluate adequacy of a wind farm with considering the combined effect of terrain, wake and WTG reliability. A quadratic interpolation method is used to study the optimal locations of WTGs in order to maximise power output of a wind farm. A test wind farm and the IEEE reliability test system (RTS) are analysed to illustrate the models and proposed technique. - Author(s): D. Barbosa ; D.V. Coury ; M. Oleskovicz
- Source: IET Generation, Transmission & Distribution, Volume 6, Issue 10, p. 1009 –1018
- DOI: 10.1049/iet-gtd.2011.0711
- Type: Article
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1009
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A power transformer needs continuous monitoring and fast protection as it is a very expensive piece of equipment and an essential element in an electrical power system. The most common protection technique used is the percentage differential logic, which provides discrimination between an internal fault and different operating conditions. Unfortunately, there are some operating conditions of power transformers that can mislead the conventional protection affecting the power system stability negatively. This study proposes the development of a new algorithm to improve the protection performance by using fuzzy logic, artificial neural networks and genetic algorithms. An electrical power system was modelled using Alternative Transients Program software to obtain the operational conditions and fault situations needed to test the algorithm developed, as well as a commercial differential relay. Results show improved reliability, as well as a fast response of the proposed technique when compared with conventional ones. - Author(s): J. Haakana ; J. Lassila ; S. Honkapuro ; J. Partanen
- Source: IET Generation, Transmission & Distribution, Volume 6, Issue 10, p. 1019 –1028
- DOI: 10.1049/iet-gtd.2011.0861
- Type: Article
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Many countries have adopted economic regulation to the electricity distribution. Economic regulation plays a significant role when long-term decisions are determined. The regulatory model sets the framework for the network planning process. It does not give strict instructions for the planning process but aims to ensure the development of the network. This paper elaborates on the influence of the incentive regulation on the electricity distribution and especially on renovation programs, which are among the main functions of the network operators in the coming years. The backgrounds of the electricity distribution network owners are very diverse, which makes the aims of the ownership different. For instance, maximising the return or profit, a strict reliability target or a tight investment schedule may reflect the objectives of the owner. Alternatively, a distribution company owned by a municipality typically wants to provide low-cost electricity for the customers, and to this end, the costs of the company should be minimised. Among others, these objectives have to be taken into account in strategic planning. Traditional distribution network planning that minimises the total costs including capital, operational and interruption costs leads to a different result, compared with planning based on maximising the profit of the owner. - Author(s): J. Xiao ; W. Gu ; C. Wang ; F. Li
- Source: IET Generation, Transmission & Distribution, Volume 6, Issue 10, p. 1029 –1035
- DOI: 10.1049/iet-gtd.2011.0767
- Type: Article
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The region-based method has been successfully applied in transmission systems. This study proposes the definition, model and applications of security region for distribution systems. With the ongoing smart grid initiatives, a large amount of real-time network information will be available. This is the motivation of an accurate calculation of the security boundary. First, this study presents the concepts of distribution system security region (DSSR); and discusses N−1 contingency scenarios for both substation transformers and feeders. Second, distribution system security boundary is modelled in the Euclidean space as several intersected hyperplanes. Furthermore, DSSR for substation transformer contingency is modelled as the space surrounded by the security boundaries and the set of all operating points that ensure the distribution system N−1 security. Third, distance from an operating point to a security boundary is formulated and a new index is also presented for security evaluation. The proposed DSSR-based security assessment method provides a new approach for future smart distribution system operation. Finally, the results from a real distribution system have demonstrated the effectiveness of the proposed concepts and methods; and the geometric characteristics of DSSR are also illustrated by means of two-dimensional visualisation of the test system. - Author(s): E. Bijami ; J. Askari ; M.M. Farsangi
- Source: IET Generation, Transmission & Distribution, Volume 6, Issue 10, p. 1036 –1045
- DOI: 10.1049/iet-gtd.2011.0770
- Type: Article
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This study presents a hybrid method based on generalised predictive control (GPC) and a proposed new hybrid shuffled frog leaping (NHSFL) algorithm to design stabilising signals to damp the multi-machine power system low-frequency oscillations. A linearised model predictive controller based on GPC is designed in which the proposed NHSFL algorithm is employed for optimising the cost function of the GPC. The numerical results are presented on a two-area four-machine and a five-area 16-machine power system. The effectiveness of the designed controllers is shown by considering various operating conditions. The proposed approach, which is called as GPC-NHSFL, is compared with a classical-based method, GPC algorithm and GPC-based standard SFL algorithm (GPC-SFL). The simulation results show the superiority and capability of the proposed approach to enhance power systems damping. - Author(s): S. Alush ; A. Braunstein ; D. Elmakias
- Source: IET Generation, Transmission & Distribution, Volume 6, Issue 10, p. 1046 –1052
- DOI: 10.1049/iet-gtd.2011.0501
- Type: Article
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Shielding failure in a transmission line occurs when lightning bypasses the ground wires and strikes the phase conductors. Most of the probability calculation methods for these failures are electro-geometric and empirical and they refer to the line as being horizontal. The purpose of this research is to examine the influence of changes on the line sag and the tension on the lightning stroke probability. A mathematical model for calculating the shielding failure rate and the expected stroke rate on ground wires based on an electro-geometric model and on a known probability density function of the stroke flows in the area was developed in this research. The results show that, for single ground wire towers, an increase in the sag (i.e. a decrease in the tension parameter) of the ground wire, relative to the phase conductors, increases the stroke rate on the phase conductors in long spans. This research proposes an analytical calculation method that considers several factors, among them the sag and the tension along the span between adjacent towers, the catenary equation and the electromagnetic theory. - Author(s): S. Kim and T.J. Overbye
- Source: IET Generation, Transmission & Distribution, Volume 6, Issue 10, p. 1053 –1059
- DOI: 10.1049/iet-gtd.2011.0746
- Type: Article
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Steady-state power flow analysis for large-scale networks requires substantial computation because of the extensive interconnections among power systems. Traditionally, network equivalent techniques have been used to reduce computational demand by eliminating the external system. These techniques, then, cannot reflect changes in the external system. This study presents a mixed approach with ac and dc power flow models for power flow analysis to decrease computational complexity and capture variations in the external system. A high level of accuracy in the targeted central part of the system is achieved using the detailed ac model. The less detailed dc model is used to reduce computational requirements and still reflect changes in the external system. Case studies with the IEEE 118-bus system are provided to compare performance among the proposed, the ac and the dc models. - Author(s): K. Chandrasekaran and S.P. Simon
- Source: IET Generation, Transmission & Distribution, Volume 6, Issue 10, p. 1060 –1073
- DOI: 10.1049/iet-gtd.2012.0193
- Type: Article
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This study proposes a novel methodology that employs fuzzified binary real coded artificial bee colony (ABC) algorithm for solving multi-objective unit commitment problem. On solving unit commitment problem, the proposed binary coded ABC algorithm finds the ON/OFF status of the generating units whereas the economic dispatch is solved using the real coded ABC. Here, three conflicting functions such as fuel cost, emission and reliability level of the system are considered. These functions are formulated as a single objective optimisation problem using the fuzzy set theory. Also, the fuzzy membership design variables are tuned using real coded ABC thereby requirement of expertise for setting these variables are eliminated. The proposed method is validated on six unit system, IEEE 30 bus system, ten unit system, 40 unit system and IEEE RTS 24 bus system. The effectiveness of the proposed technique is demonstrated by comparing its performance with other methods reported in the literature.
Improvement of the differential busbar characteristic to avoid false operation during to CT saturation
Hyperbolic S-transform-based method for classification of external faults, incipient faults, inrush currents and internal faults in power transformers
Effect of micro-fillers in polytetrafluoroethylene insulators on the characteristics of surface discharges in presence of SF6, CO2 and SF6-CO2 mixture
Efficient and optimal approach for location and parameter setting of multiple unified power flow controllers for a deregulated power sector
Automatic classification of power quality events and disturbances using wavelet transform and support vector machines
New method for monitoring voltage stability condition of a bus of an interconnected power system using measurements of the bus variables
Smart demand side management of low-voltage distribution networks using multi-objective decision making
Adequacy study of a wind farm considering terrain and wake effect
New approach for power transformer protection based on intelligent hybrid systems
Renovation strategies and economic regulation in electricity distribution
Distribution system security region: definition, model and security assessment
Design of stabilising signals for power system damping using generalised predictive control optimised by a new hybrid shuffled frog leaping algorithm
Transmission line sag influence on lightning stroke probability
Mixed power flow analysis using AC and DC models
Multi-objective unit commitment problem with reliability function using fuzzified binary real coded artificial bee colony algorithm
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