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Online ISSN 1751-8695 Print ISSN 1751-8687

IET Generation, Transmission & Distribution

Volume 3, Issue 6, June 2009

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Volume 3, Issue 6

June 2009

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    • Electric field analytical formulas for single-circuit power lines with a horizontal arrangement of conductors
      • Author(s): A.E. Tzinevrakis ; D.K. Tsanakas ; E.I. Mimos
      • Source: IET Generation, Transmission & Distribution, Volume 3, Issue 6, p. 509 –520
      • DOI:  10.1049/iet-gtd.2008.0361
      • Type: Article
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      • p. 509 –520 (12)
        Analytical formulas are derived for the calculation of the electric field at any point in the vicinity of single-circuit power lines with a horizontal arrangement of conductors. The analytical formulas are appropriate for the assessment of public exposure as they allow direct calculation of the electric field. They are also suitable for assessing the dependence of the electric field on electric and geometric parameters. Initially, an accurate formula of the electric field is derived by using a proposed method. This method is based on the use of multipole expansions and double complex numbers for the representation of the electric field vector and symmetrical components analysis for the conductors' charges. Based on the accurate formula, a sensitivity analysis of the electric field is carried out with respect to the various parameters. Two simpler approximate formulas are finally developed, which provide the electric field with satisfactory accuracy in certain areas in the vicinity of the lines.
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      Integral methodology for distribution systems reconfiguration based on optimal power flow using Benders decomposition technique
      • Author(s): H.M. Khodr  and  J. Martínez-Crespo
      • Source: IET Generation, Transmission & Distribution, Volume 3, Issue 6, p. 521 –534
      • DOI:  10.1049/iet-gtd.2008.0289
      • Type: Article
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      • p. 521 –534 (14)
        A new and efficient methodology for distribution network reconfiguration integrated with optimal power flow (OPF) based on a Benders decomposition approach is presented. The objective minimises power losses, balancing load among feeders and subject to constraints such as capacity limit of branches, minimum and maximum power limits of substations or distributed generators, minimum deviation of bus voltages and radial optimal operation of networks. A variant of the generalised Benders decomposition algorithm is applied to solve the problem. The formulation can be embedded under two stages; the first one is the master problem and is formulated as a mixed integer non-linear programming problem. This stage determines the radial topology of the distribution network. The second stage is the slave problem and is formulated as a non-linear programming problem. This stage is used to determine the feasibility of the master problem solution by means of an OPF and provides information to formulate the linear Benders cuts that connect both problems. The model is programmed in GAMS mathematical modelling language. The effectiveness of the proposal is demonstrated through two examples extracted from the specialised literature.
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      Analogue emulation of power system load behaviour
      • Author(s): A.S. Deese  and  C.O. Nwankpa
      • Source: IET Generation, Transmission & Distribution, Volume 3, Issue 6, p. 535 –546
      • DOI:  10.1049/iet-gtd.2008.0541
      • Type: Article
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      • p. 535 –546 (12)
        In analogue emulation, a non-linear system model is implemented as a set of reconfigurable analogue circuits. This hardware is actuated, initialised and allowed to settle to a steady state, during which time the user utilises voltage and current measurement devices to observe the system's transient response and static solution. In this study, the authors present the advantages of analogue emulation over digital simulation for fast steady-state and dynamic power system analyses, as required in real-time network operation. They discuss the design, fabrication, construction and testing of a multi-bus power system emulator with focus on a reconfigurable analogue circuit to mimic load. They utilise circuit theory to analyse its operation and present a set of design modifications aimed at improved accuracy.
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      Design and analysis of dynamic voltage restorer for deep voltage sag and harmonic compensation
      • Author(s): F.A.L. Jowder
      • Source: IET Generation, Transmission & Distribution, Volume 3, Issue 6, p. 547 –560
      • DOI:  10.1049/iet-gtd.2008.0531
      • Type: Article
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      • p. 547 –560 (14)
        A dynamic voltage restorer (DVR) to compensate deep voltage sags and harmonics is proposed. The DVR consists of shunt and series converters connected back-to-back through a dc-to-dc step up converter. The presence of the dc-to-dc step converter permits the DVR to compensate deep voltage sags for long duration. The series converter is connected to the supply side whereas the shunt converter is connected to the load side. With this configuration, there is no need for large dc capacitors. A design procedure for the components of the DVR is presented under a voltage sag condition. The control system of the proposed DVR is based on hysteresis voltage control. Besides voltage sag compensation, the capability of compensating load voltage harmonics has been added to the DVR to increase the power quality benefits to the load with almost negligible effect on the sag compensation capability. The proposed DVR is modelled and simulated using SIMULINK/MATLAB environment. Time domain simulations are used to verify the operation of the DVR with linear and non-linear loads.
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      Output feedback SSR damping controller design based on modular discrete-time dynamic model of TCSC
      • Author(s): S.R. Joshi ; E.P. Cheriyan ; A.M. Kulkarni
      • Source: IET Generation, Transmission & Distribution, Volume 3, Issue 6, p. 561 –573
      • DOI:  10.1049/iet-gtd.2008.0439
      • Type: Article
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      • p. 561 –573 (13)
        This paper presents the use of a modular, sample invariant, six samples per cycle, discrete-time model of a thyristor controlled series capacitor (TCSC) for output feedback-based subsynchronous resonance (SSR) damping controller (SSDC) design. An SSDC is used to alleviate the instability of torsional modes caused by external fixed capacitors used in conjunction with a TCSC. It is found that damping torque analysis-based design of an SSDC using a non-local signal like generator slip is straightforward and the resulting SSDC has a simple compensator structure. On the other hand, the residues and pole-zero configuration with the line current magnitude as a feedback signal are such that it is relatively more difficult to obtain a robust design, especially if several subsynchronous torsional modes are present. Eigenvalue analysis and digital simulation studies indicate that the TCSC model can accurately predict the behaviour of a TCSC with and without a damping controller.
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      Transmission cost allocation based on use of reliability margin under contingency conditions
      • Author(s): H. Monsef  and  M. Jaefari
      • Source: IET Generation, Transmission & Distribution, Volume 3, Issue 6, p. 574 –585
      • DOI:  10.1049/iet-gtd.2007.0352
      • Type: Article
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      • p. 574 –585 (12)
        A reliability-based method for allocating the cost of transmission networks is presented. The cost of a transmission line is divided into two components. The first component corresponds to a part of the line capacity, which is used under normal conditions. The second component corresponds to a portion of the line capacity, which is only used under contingency conditions. The latter is the part that market agents use to calculate the reliability benefit charges of the line. In the proposed method, a probabilistic index is defined based on single-contingency analysis, which measures the reliability margin of each line for each transaction. Furthermore, the cost components associated with capacity use and reliability benefit charges are determined based on the actual reliability margin of lines. This method can be used to provide an equitable means for allocating the cost of transmission network among users of a bilateral market model. The proposed method is illustrated in a small power system as well as the 24-bus IEEE-RTS, and its conceptual and computational feasibility are demonstrated.
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      Offshore wind farm with centralised power conversion and DC interconnection
      • Author(s): D. Jovcic  and  N. Strachan
      • Source: IET Generation, Transmission & Distribution, Volume 3, Issue 6, p. 586 –595
      • DOI:  10.1049/iet-gtd.2008.0372
      • Type: Article
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      • p. 586 –595 (10)
        The study of a hypothetical large offshore wind farm based on centralised power conversion and interconnected to the grid using a multiterminal parallel high voltage direct current (HVDC) link is presented. The 300 MW wind farm consists of 60 squirrel-cage based 5 MW generators connected to a common DC bus using ten voltage source converters (VSCs). The transmission system converters provide variable speed generator control, and therefore individual converters are not required for each wind generator, implying savings in wind farm costs. The paper studies the technical and economical benefits of the proposed topology, as well as the selection of the main components. A detailed analysis of the control circuits for both generator and grid facing converters, with respect to primary control functions, is also given. PSCAD/EMTDC simulation of the proposed concept is presented for realistic wind signals. The results confirm operation at an average optimum coefficient of performance at each respective generator group, as well as satisfactory stability even for severe wind speed changes. The proposed concept reduces the costs associated with DC interconnection and may simplify integration of large offshore wind farms at substantial distances.
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      Transient stability assessment using projection formulations
      • Author(s): D.Z. Fang ; J.G. Yang ; W. Sun ; Z.Y. Xue ; S.Q. Yuan
      • Source: IET Generation, Transmission & Distribution, Volume 3, Issue 6, p. 596 –603
      • DOI:  10.1049/iet-gtd.2008.0583
      • Type: Article
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      • p. 596 –603 (8)
        Definitions of angle radius and coordinates axis are presented to propose a new transient stability method that is simple and reliable for transient stability assessment. The concept of angle radius is further developed to introduce the novel concept of projection energy function (PEF), which in turn allow to the assessment of critical clearing time and generation limit of system in a new way. The advantage of the new method is that no concept of advanced generator group is required in the assessment contingency stability index. Case studies on the ten-generator New England test power system are reported to verify the validity of the PEF method.
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