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Generation, Transmission and Distribution, IEE Proceedings-

Issue 6 • Date 12 Nov. 2003

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Displaying Results 1 - 18 of 18
  • Lightning protection of transmission lines: optimal shielding design procedure

    Page(s): 659 - 667
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (533 KB)  

    The paper first derives a set of shielding constraints which must be satisfied for achieving effective shielding against lightning for all of the phase conductors of an overhead transmission line in relation to earth-wire placement. The shielding constraints are obtained from the analysis related to the rigorous proof of the premise that, once the earth-wire position has been determined to achieve effective shielding for a nominated critical lightning stroke current, then shielding of the phase conductors is still maintained for stroke currents greater than the critical value. An optimal shielding design procedure is then developed in which the cost function relating to earth-wire position(s) is minimised subject to shielding constraints and specified clearance constraints. Results of lightning protection designs using the procedure, to achieve effective shielding for a range of transmission-line configurations, are presented. View full abstract»

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  • Generator ranking using modal analysis

    Page(s): 709 - 716
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (558 KB)  

    As is well known, generators are important reactive support devices in power systems. Due to difference in location, active output and other factors, however, specific generators are of differing importance to the system. There is a need to develop an index to measure the relative importance of the generators. Modal analysis is extended to include entries for generators. A generator ranking method is then developed based on the participation factors related to the critical mode in the vicinity of the point of voltage collapse. Simulation and verification studies are conducted on different scale systems including a 1000-bus real-life system. The results show the validity of the proposed method and that the participation factors are a comprehensive index taking into account all related factors. An example is also provided to illustrate the application of this ranking index. View full abstract»

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  • Accurate representation of soil behaviour for transient studies

    Page(s): 736 - 744
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (608 KB)  

    A paper representation of soil behaviour for transient studies is presented. Such representation is more accurate than the most common procedures of engineering practice and, in several conditions, lead to results with important differences. The proposed model takes into account the earth's conductivity and permittivity frequency dependence, which normally are not considered. One of the aspects covered in the paper is the importance of properly considering the Earth's electromagnetic behaviour when calculating transmission line parameters. Some comparisons are presented for an actual 440 kV three-phase transmission line in which the soil behaviour is represented through a unique real value of conductance (the normal approach) and through the proposed model. View full abstract»

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  • Estimating customer outage costs due to a specific failure event

    Page(s): 668 - 672
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (391 KB)  

    Customer interruption costs due to failure in electrical energy supply depend on many factors. A procedure is developed to estimate the customer outage costs on a distribution feeder subjected to a specific outage event. The data required to perform a detailed evaluation is illustrated and discussed, including the customer composition on the feeder, the customer demand profiles at the feeder load points and the relevant customer damage functions. The procedure presented in the paper is illustrated by application to a specific distribution feeder in the city of Saskatoon. The customer costs associated with power supply failures are a function of the time of day, day of the week and time of year. They are also strongly influenced by the duration of the outage event. The effect of outage duration and the time of outage occurrence is illustrated. View full abstract»

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  • Application of GCN approach for power distribution system contingency load transfer

    Page(s): 717 - 721
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (419 KB)  

    The daily load profiles of distribution feeders are determined by using customer information in a customer information system (CIS) and information between customers and distribution transformers in an outage management information system (OMIS) in the Taiwan Power Company (Taipower). Regulating the load distribution among feeders is implemented by the G-coloured nets inference mechanism (GCNIM) in order to improve the operating performance for overloading conditions of distribution feeders, transferring the load among feeders via switching operations proposed by the GCNIM after the fault has been identified and isolated when a distribution system fault occurs. A practical Taipower distribution system, with daily load profiles, is used to perform the computer simulations, and thus demonstrate the effectiveness of the proposed approach. It is found that load distribution among feeders and performance of fault restoration can be improved via switching operations proposed by the GCNIM. View full abstract»

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  • Inclusion of a high voltage DC-voltage source converter model in a Newton-Raphson power flow algorithm

    Page(s): 691 - 696
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (443 KB)  

    Models for high voltage DC-voltage source converter (HVDC-VSC) controllers suitable for direct incorporation into Newton-Raphson power flow algorithms are presented. The models are developed from first principles, starting with a simple VSC model and progressing to encompass the full HVDC-VSC link model. The applied modelling approach is modular in nature and in addition to the shunt-connected voltage source model, which may be used to represent a STATCOM, a series-connected voltage source model is also developed. This enables significant modelling flexibility since by suitably combining shunt and/or series voltage sources several VSC-based flexible AC transmission system (FACTS) controller models are realised quite straightforwardly, namely the back-to-back HVDC-VSC, the full HVDC-VSC link and the unified power flow controller. Attention is focused on the HVDC-VSC models. The models are implemented into an existing OOP power flow computer program written in C++ that incorporates a wide portfolio of FACTS models. The models are tested for reliability towards the convergence and accuracy of results using several power systems with varying degrees of operational complexity and power flow control requirements. View full abstract»

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  • Computing the value of security

    Page(s): 673 - 678
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (521 KB)  

    Power systems are operated with some margin of security to ensure that the most likely losses of plant will not cause interruptions to supply. However, this security margin has a cost that may not be justified by the benefit in terms of prevention of lost load. The authors argue that the level of security could be set on the basis of a cost/benefit analysis that balances the cost of operating the system against the expected outage cost. The expected outage cost is determined using a Monte Carlo simulation of the system operation in which random outages are simulated. Such a simulation should not be limited to small but relatively frequent outages but should also include major disturbances that affect a large part of the system. In order to achieve a sufficient degree of accuracy, the simulation models the actions taken to save the system during emergencies, the duration of the restoration process, and possible protection malfunctions. It is shown that sympathetic trippings due to protection malfunction can have a very significant impact on the probability of major incidents and hence on the value of security. View full abstract»

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  • Harmonic assessment using electromagnetic transient simulation and frequency-dependent network equivalents

    Page(s): 641 - 650
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (536 KB)  

    Electromagnetic transient simulation can be used to model complex nonlinearities that are very difficult to represent adequately in the frequency domain. After reaching the steady state the voltage and current waveforms, represented by sets of discrete values at equally spaced intervals (corresponding with the integration steps), are subjected to fast Fourier transform processing to derive the harmonic spectra. However, the accuracy of the EMTP approach is limited by the restricted frequency dependence representation of the AC system components. It is shown that this problem is greatly reduced with the use of frequency-dependent network equivalents for the linear part of the system. View full abstract»

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  • Discrete-Fourier-transform-based technique for removal of decaying DC offset from phasor estimates

    Page(s): 745 - 752
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (520 KB)  

    A technique to suppress the negative effect of a decaying DC offset on phasor estimates using a digital Fourier transform algorithm is presented. The proposed technique is based on evaluation of the decaying DC component in the signal. The technique is suitable for all prevailing systems and fault conditions. The performance of the technique is evaluated in both the time and frequency domains. Simulation results showing the effectiveness of this new technique are presented. The proposed technique is further evaluated when it is used in a distance relay design. View full abstract»

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  • Determination of the branch power and loss caused by node injection power

    Page(s): 722 - 726
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (394 KB)  

    Current methods to determine branch power and loss changes include the DC method, the boundary power flow method and the sensitivity method, however, none of these methods are theoretically correct. Within the framework of an AC power-flow solution the node generation power and node load power are modelled using either a constant impedance or a current source, respectively after being connected to the relevant node. By solving the network current equation, the node voltage can be expressed as a function of the node load power. Similarly, the node voltage can be expressed as a function of the node generation power. Also, the branch power flow and loss caused by the node generation power or the node load power can be obtained by using the proposed expression for the nonlinear function. The branch power loss is allocated to the node power. An example is presented to validate the proposed approach. View full abstract»

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  • Calculations of diversified harmonic currents in electric distribution systems

    Page(s): 651 - 658
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (526 KB)  

    A comprehensive analysis of the characteristics of distribution-system harmonics is provided. This analysis leads to the formulation of harmonic diversity factor tables. These tables give a reliable estimate of harmonic currents in distribution feeders and enable the engineers to determine the amount of background distortion of the voltage waveform. The use of the proposed tables will ease the computational difficulties in performing distribution system harmonic studies. Both deterministic and probabilistic methods were integrated in the conducted analysis in this paper to generate the diversity factor tables. The proposed method and the analysis results are presented in detail. View full abstract»

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  • Storage power flow controller using battery storage

    Page(s): 727 - 735
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (497 KB)  

    Two new topologies of energy storage systems connected to the grid which can provide concomitant benefits associated with a unified power flow controller are described. The unified power flow controller can provide fast control of real and reactive power along a distribution corridor by continuously providing phase angle control, series compensation and shunt reactive power compensation, while at the same time providing several other very important benefits to power system operation such as, harmonic compensation, load levelling, voltage stability improvement and back-up supply. These storage power flow controllers can provide improved power system operation and control, added system security and reduced power system losses. View full abstract»

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  • Reliability evaluation algorithm for complex medium voltage electrical distribution networks based on the shortest path

    Page(s): 686 - 690
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (395 KB)  

    This paper presents a reliability evaluation algorithm for medium voltage radial electrical distribution networks (EDN). The algorithm is suitable for evaluating reasonably complex EDNs with multiple subfeeders. It applies a forward-search-method to identifying the section controlled by a breaker. By applying graph theory and considering the structural features of the EDNs, methods for searching for the shortest paths from any node to the energy source and between any two nodes are developed. Based on the definitions of feeder terminal node (FTN) and the shortest path from a failure element to FTNs, it is easy to identify a disconnected section, following which a classification of the nodes is obtained. The reliability indices of the buses, feeders and system are calculated, based on the nodal classification. The developed algorithm has been tested on a number of test systems and the results show the effectiveness and applicability of the approach. View full abstract»

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  • Extension neural network for power transformer incipient fault diagnosis

    Page(s): 679 - 685
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (449 KB)  

    An extension neural network (ENN)-based diagnosis system for power transformer incipient fault detection is presented. The ENN proposed is a combination of extension theory and a neural network. Using an innovative extension distance instead of Euclidean distance (ED) to measure the similarity between tested data and the cluster centre, it can effect supervised learning and achieve shorter learning times than traditional neural networks. Moreover, the ENN has the advantage of height accuracy and error tolerance. Thus, the incipient faults of power transformers can be diagnosed quickly and accurately. To demonstrate the effectiveness of the proposed method, 40 sets of field DGA data from power transformers in Australia, China, and Taiwan have been tested. The test results confirm that the proposed method has given promising results. View full abstract»

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  • Decentralised nonlinear equilibrium point adaptive control of generators for improving multimachine power system transient stability

    Page(s): 697 - 708
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (612 KB)  

    Decentralised nonlinear control of generator excitation and turbine governor based on the feedback linearisation approach is proposed. To make the proposed nonlinear control possess adaptive ability under the changing conditions of power systems, the extended observation decoupled state space in which mechanical power is considered as variable is proposed, and the local stability of the postfault equilibrium point is established rigorously from a mathematical viewpoint. Nonlinear simulations are performed in a three-machine power system and in the ten-machine West Japan power system, and the effectiveness of the proposed nonlinear control and the convergence characteristics of the post-fault equilibrium point observer are validated. View full abstract»

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  • Robust multivariable control design for HVDC back to back schemes

    Page(s): 761 - 767
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (525 KB)  

    A robust multivariable control design procedure for HVDC back-to-back schemes is presented. HVDC links are commonly controlled with a decentralised structure, whereby in normal operation the rectifier may track direct current and the inverter may track direct voltage, firing angle or extinction angle. In the case of a back-to-back HVDC link the measurements of control variables of both sides are physically close, hence it is possible to apply a true multivariable controller whereby current and voltage are controlled by rectifier and inverter together. H-infinity control theory is used for a systematic tuning procedure which incorporates robustness against uncertainty in the short-circuit levels of both rectifier and inverter side AC systems. The linear control transfer functions for rectifier and inverter controllers are arrived at simultaneously thereby removing iterative design steps to find the best combination of control parameters for both rectifier and inverter controllers. The decoupling effect resulting from the multivariable controller structure reduces the interaction between tracking of direct current and direct voltage. It is verified by nonlinear EMTDC simulation that the designed controller is robust and can contribute to good fault recovery when integrated with other control loops and nonlinear control functions as implemented in manufactured controls. View full abstract»

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  • Fast solution technique for large-scale unit commitment problem using genetic algorithm

    Page(s): 753 - 760
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (410 KB)  

    An approach for a large-scale unit commitment problem is presented. The unit commitment (UC) problem plays a major role in power systems, because the improvement of commitment schedules results in the reduction of operating costs. However, the unit commitment problem is one of the most difficult optimisation problems in power systems, because this problem has many constraints. Moreover, search space is vast. To overcome these problems, a new genetic operator based on unit characteristic classification and unit integration technique are proposed. The proposed algorithm was tested on a reported UC problem. From simulation results, better solutions are obtained in comparison with previously reported results. Numerical results for systems up to 100 units are compared to previously reported results. View full abstract»

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