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Generation, Transmission and Distribution, IEE Proceedings-

Issue 5 • Date Sep 1998

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Displaying Results 1 - 22 of 22
  • Design of reduced-order observer-based variable structure power system stabiliser for unmeasurable state variables

    Publication Year: 1998 , Page(s): 525 - 530
    Cited by:  Papers (4)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (420 KB)  

    In the paper, in order to design a simpler and more economical observer-based controller and to solve the problem associated with the unmeasurable state variables in the conventional VSC, a reduced-order (n-m) observer-based variable structure controller (ROOVSC) is proposed and applied to a power system stabiliser (PSS). This ROOVSPSS is obtained by combining the variable structure control (VSC) with a reduced-order observer (ROO): the state estimator by the ROO and the controller by the VSC, which eliminates the need to measure all the state variables in the conventional VSC-PSS. The simulation results are shown by comparison of the ROOPSS with the proposed ROOVSPSS under normal and heavy load operations View full abstract»

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  • Comparison between evolutionary programming and a genetic algorithm for fault-section estimation

    Publication Year: 1998 , Page(s): 616 - 620
    Cited by:  Papers (8)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (488 KB)  

    The paper proposes an application of evolutionary programming (EP) to fault-section estimation in power systems. Several techniques have been employed to solve this problem so far. A genetic algorithm (GA) has been reported to be one of these techniques. In order to measure the efficiency of EP and make comparisons, a GA has also been used to solve the same problem. Different parameters which affect the EP convergence have been investigated. Two object-oriented software codes have been developed to implement the algorithms. A sample power system is used to examine the algorithms. It shows that EP is superior to the GA for the type of coding strategy and evolution as defined for the GA View full abstract»

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  • Control strategy for grid-connected DC-AC converters with load power factor correction

    Publication Year: 1998 , Page(s): 487 - 491
    Cited by:  Papers (50)  |  Patents (2)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (472 KB)  

    The paper presents the modelling, analysis and design of a pulse width modulation voltage source inverter (PWM-VSI) to be connected between a DC source, which is supplied from a photovoltaic (PV) array and the AC grid. The control algorithm of the PWM-VSI applies the concepts of the instantaneous p-q (real-imaginary) power theory. The objective is to show that, with adequate control, the power converter can transfer the DC energy from a PV array and improve the power factor (and the power quality) of the electrical system. Some design considerations are also discussed. A digital simulation and measurements on a small prototype model verified the feasibility of the proposed control method View full abstract»

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  • Digital distance relaying algorithm for first-zone protection for parallel transmission lines

    Publication Year: 1998 , Page(s): 531 - 536
    Cited by:  Papers (24)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (412 KB)  

    The paper proposes a new digital distance relaying algorithm for the first-zone protection of parallel power transmission lines. The new method uses data from one end of the protected parallel lines to calculate the fault distance. It is shown that the new method is independent of fault resistance, remote infeed and source impedances, Extensive simulation studies using EMTP have verified that this approach can obtain a highly accurate fault distance estimation within one cycle after fault inception and hence is very much suitable for the digital distance protection of parallel power lines. Applications of this method for fault location are also presented View full abstract»

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  • Robust algorithm for load estimation in distribution networks

    Publication Year: 1998 , Page(s): 499 - 504
    Cited by:  Papers (4)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (600 KB)  

    A new mathematical model is proposed which allows distribution network loads to be estimated using the available information from metering and other data sources. The application of this model offers a compromise between conventional load allocation methods and network state estimation. A novel approach to the modelling of current magnitude measurements is introduced. The problem is formulated as a weighted least absolute values estimation problem which is solved numerically using weighted least squares with an iterative reweighting scheme. The nonlinear effect of power losses is accounted for by applying a Newton-Raphson approach. Alternative sparse matrix solution techniques are compared and a robust and computationally efficient approach is described which is suitable for online applications View full abstract»

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  • Steady-state model of direct connected generator-HVDC converter units in the harmonic domain

    Publication Year: 1998 , Page(s): 559 - 565
    Cited by:  Papers (4)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (544 KB)  

    A new twelve-pulse unit connection model is formulated and solved in the harmonic domain. The model takes into account the effects of generator saliency and saturation, interaction of the converter with the DC system, and variation in the firing and end of commutation angles caused by AC voltage and DC current harmonics. The reactive power control by generator excitation in the absence of converter transformer on-load tap-changers is also modelled. The solution of a test system is validated by means of time domain simulations View full abstract»

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  • Model-based analysis of protection system performance

    Publication Year: 1998 , Page(s): 547 - 552
    Cited by:  Papers (10)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (576 KB)  

    Following a power system fault, protection engineers have to analyse the protection scheme activity to ensure correct operation. To aid them in this task, data gathering systems are increasingly being fitted to power systems. However, during extreme operating conditions, the volume of data made available by these systems can be overwhelming. To help overcome this, knowledge-based systems have been developed and installed at ScottishPower's corporate headquarters to extract the relevant `information' from the supervisory control and data acquisition (SCADA) system `data'. The paper reports on the next stage of decision support for the protection engineers which builds upon the diagnosis provided by the knowledge-based systems. This enhanced support is provided by a model-based diagnostic system which provides automatic analysis of the available fault recorder data. This system utilises the most appropriate techniques employed by existing model-based diagnostic systems. A novel approach for handling tolerances associated with the operating times of protection scheme components is introduced, thus enabling modelling measurement inaccuracies to be dealt with View full abstract»

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  • Stochastic multiobjective generation dispatch of combined heat and power systems

    Publication Year: 1998 , Page(s): 583 - 591
    Cited by:  Papers (7)  |  Patents (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (748 KB)  

    A new stochastic formulation of multiobjective optimisation for combined heat and power system dispatch is presented. Both the power and heat demands are treated as random variables. The three objective functions to be minimised are: the total generation cost, the expected power generation deviation and the expected heat generation deviation. As these objectives are in conflict with each other, only a noninferior solution can be reached. The goal attainment method is used to solve this multiobjective optimisation problem by assuming that the decision-maker (DM) has desired a certain goal for each of these objectives. Very often, the DM finds it difficult to define the relative importance or a merit function among improving individual objectives and reducing constraint violations. A fuzzy decision index is proposed to provide the best-compromise solution among all objectives and constraints, and a means of maximising the most underachieved objective. A genetic algorithm approach is also proposed to help the DM to search for such a solution mathematically. Application results of the method to a seven-generator sample system are presented View full abstract»

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  • Synchronous generator internal fault computation and experimental verification

    Publication Year: 1998 , Page(s): 604 - 610
    Cited by:  Papers (15)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (524 KB)  

    Along with the development of the electric power industry, accurate analysis of faulted generators becomes more and more important. The paper presents a method for simulating internal faults in synchronous generators, consisting of a single path per phase, using direct phase quantities. Simulation results showing the fault currents, during single phase to ground faults and two phase to ground faults, are compared with actual fault currents to verify the proposed method View full abstract»

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  • Power flow control with controllable reactive series elements

    Publication Year: 1998 , Page(s): 493 - 498
    Cited by:  Papers (5)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (608 KB)  

    The basic features of controllable reactive series elements (CRSE) (i.e. controllable series compensation (CSC) and static synchronous series compensators (SSSC)) for power system load flow control are presented. Mathematical models of CRSE, including a simplified transmission system model, have been developed. Based on this, the CRSE impact on a longitudinal transmission system was studied. The physical background of the basic differences between a CSC and an SSSC in terms of power flow control has been presented. According to theoretical considerations, from the point of view of power flow control capability, SSSC is superior to CSC, especially at low transmission angles. Therefore SSSC seems to be suitable in situations where power flow needs to be controlled in short lines or in light-load conditions View full abstract»

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  • Comparative study of continuous distribution models for power system reliability evaluation

    Publication Year: 1998 , Page(s): 566 - 572
    Cited by:  Papers (5)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (572 KB)  

    The paper presents a generalised expansion method using a gamma distribution as a useful tool for the approximation of capacity outage probability distribution of a generation system. The well known Gram-Charlier expansion and Legendre series are briefly reviewed and compared with the generalised expansion using a sample system IEEE-RTS (reliability test system). The results show that the generalised expansion with a composite of gamma distributions is more accurate and stable than the Gram-Charlier expansion and Legendre series as higher order expansion terms are included View full abstract»

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  • Application of STATCOMs to wind farms

    Publication Year: 1998 , Page(s): 511 - 516
    Cited by:  Papers (63)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (612 KB)  

    Effective reactive power control in distribution networks can have an important influence on the level of embedded generation that is acceptable and on the costs of its connection. A comprehensive study was undertaken to investigate how STATCOMs could be used with fixed-speed wind turbines, which use induction generators, to improve both the steady-state state and dynamic impact of a wind farm on the network. An optimal power flow model based on loss minimisation was developed and used to show that operation of a wind farm at unity power factor is unlikely to allow maximum penetration of wind energy into a weak distribution circuit. The results of the electromagnetic simulations showed that the use of a STATCOM improves the steady-state stability limits of the network. They also showed that the use of a STATCOM with an appropriately designed control strategy can prevent damaging overvoltages that may occur under islanding conditions. The results also demonstrated that a STATCOM can be used to mitigate voltage fluctuations at blade passing frequency, which may occur if the rotors of a number of wind turbines fall into synchronism View full abstract»

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  • Real-time contingency evaluation and ranking technique

    Publication Year: 1998 , Page(s): 517 - 524
    Cited by:  Papers (14)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (680 KB)  

    The tendency towards maximising economic benefits has led power systems utilities to run close to the limits of stable operation. This has necessitated the study of the stressed situation of the power system network to accomplish efficient energy management without losing its reliability. Online monitoring of power system stability has become a vital factor for electric utilities. An effective method for real-time monitoring of system status and thus voltage collapse prediction is described. The proposed technique investigates each line of the system through calculating an indicator that varies from 0 (no load condition) to 1 (maximum permissible loading condition). The basic concept of maximum power transfer through a line is utilised. The proposed contingency evaluation technique is applied on the IEEE 24 bus and IEEE 6 bus reliability test system and is found to be accurate in assessing the stressful status of the lines View full abstract»

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  • Voltage stability and thermal limit: constraints on the maximum loading of electrical energy distribution feeders

    Publication Year: 1998 , Page(s): 573 - 577
    Cited by:  Papers (11)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (428 KB)  

    The loading condition of distribution systems is assessed with respect to voltage stability as well as to thermal limit. Real networks of a distribution utility of Brazil are used in the tests performed. Results show that the maximum loading may be limited by voltage stability rather than by thermal limit. The paper shows the necessity of considering voltage stability as a new constraint on the operational loading of electrical energy distribution feeders, including the connection of new consumers. The voltage stability constraint should be considered in studies concerning distribution systems expansion. The new planning constraint may avoid the building of new lines and transformers which could never be fully used in systems already stressed by voltage stability View full abstract»

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  • Electromagnetic transient simulation of power systems using root-matching techniques

    Publication Year: 1998 , Page(s): 481 - 486
    Cited by:  Papers (5)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (500 KB)  

    For power system electromagnetic transient simulations, the method of substituting the trapezoidal integrator, developed by Dommel, is generally applied. The trapezoidal rule is based on a truncated Taylor series and therefore contains truncation errors. These truncation errors cause numerical oscillations when the time step is large relative to some of the time constants in the network. This leaves the user unsure whether observed oscillations are numerical or true artefacts of the system simulated. Various techniques have been developed to reduce the numerical oscillations, each with strengths and drawbacks. An exponential form of the difference equation is developed, using root-matching techniques and demonstrated on a simplified power system. This technique eliminates the truncation error and provides highly efficient and accurate time domain simulation regardless of the time step used. This exponential form of the difference equation generates a solution at each time point that is exact for the step response and a good approximation for an arbitrary forcing function View full abstract»

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  • Excitation control system for use with synchronous generators

    Publication Year: 1998 , Page(s): 537 - 546
    Cited by:  Papers (10)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (900 KB)  

    An optimal excitation control strategy for a synchronous generator is derived using Lyapunov's direct method and the nonlinear system equations. The control strategy requires neither phase compensation nor wash-out circuits characteristic of standard power system stabilisers (PSS). By using a nonlinear system model, the control strategy is optimal over a wide range of rotor angle and swing frequency changes. The excitation control system required to implement the control strategy is hierarchical and has a different structure to the traditional excitation control system with PSS. In the proposed structure, a primary controller damps quickly any power swings using the synchronous EMF as the feedback signal. A secondary controller maintains constant generator voltage by adjusting the reference value of the synchronous EMF fed to the primary controller to that required by the actual operating conditions. The proposed excitation control system has been tested on a single generator-infinite busbar power system with the simulation results showing excellent damping of power swings over a wide range of operating conditions whilst retaining good voltage control View full abstract»

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  • Voltage stability assessment with inclusion of hard limits

    Publication Year: 1998 , Page(s): 505 - 510
    Cited by:  Papers (2)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (536 KB)  

    The work presents new methodologies in order to represent, with more accuracy, the hard limits of voltage regulators in modal analysis. These hard limits are treated in the linearisation process by Taylor and power series and hyperbolic functions. The procedures required to adapt a conventional load flow in order to include a more realistic behaviour of generators in the determination of initial conditions are described. A methodology is presented which considers the dependence of generator reactive power limits on the operating conditions. Such procedures aim at a more realistic analysis of the power system especially at high loadings. Results are presented for a power system which validate the proposed methodologies View full abstract»

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  • Electric-power-quality improvement using parallel active-power conditioners

    Publication Year: 1998 , Page(s): 597 - 603
    Cited by:  Papers (4)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (544 KB)  

    A parallel active-power conditioner is proposed for electric-power-quality improvement. In the proposed conditioner, a three-phase voltage of high quality can be promised under various nonideal utility conditions, including utility undervoltage, overvoltage, outage, pollution and unbalance scenarios. A systematic procedure for the design of active-power conditioners is also provided. Test results have demonstrated the effectiveness of the method in improving electric-power quality on the load side. This approach also has the potential to be extended or integrated to other circuit designs View full abstract»

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  • Design of decentralised output feedback TCSC damping controllers by using simulated annealing

    Publication Year: 1998 , Page(s): 553 - 558
    Cited by:  Papers (4)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (580 KB)  

    A novel method for the design of output feedback controllers for thyristor controlled series compensators (TCSCs) in a meshed power system is developed in the paper. The selection of the output feedback gains for the TCSC controllers is formulated as an optimisation problem and the simulated annealing (SA) algorithm is used to find the solution. Using this method, the conflicting design objectives, such as the improvement in the damping of the critical modes, any deterioration of the damping of the noncritical modes and the saturation of the controller actuators, can be simultaneously considered. It is also shown that the proposed SA algorithm can be used to design robust controllers which satisfy the required performance criteria over several operating conditions. The proposed control scheme can be easily implemented as only the measurable signals local to each TCSC location are used to control the TCSCs (decentralised control) View full abstract»

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  • Intelligent system for fault diagnosis on low voltage distribution networks

    Publication Year: 1998 , Page(s): 592 - 596
    Cited by:  Papers (3)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (496 KB)  

    The task of fault diagnosis on the distribution networks operating at 11 kV and lower voltages is very different from the higher voltage levels because very little telemetered data is available and knowledge of a fault occurrence often depends on customers complaining of loss of supply. Unfortunately, the connectivity of customers to the network is not normally available on geographic information systems (GIS), so connectivity is indirectly established through post codes. A novel kind of object oriented blackboard architecture using deep and shallow knowledge has been developed. The notion of object-oriented active databases has also been introduced. The intelligent system developed can assist the control engineer in diagnosing the fault quickly to ameliorate the immediate effects of the fault. The special feature of this research is that the developed architecture is suitable for any fault diagnosis situation where information of the system is incomplete and is accrued over a period of time. Partial solutions are obtained as the first piece of information is received and these partial solutions are improved as further information is received View full abstract»

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  • Modelling of pumped-storage generation in sequential Monte Carlo production simulation

    Publication Year: 1998 , Page(s): 611 - 615
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (432 KB)  

    Power system planning inherently needs to consider all aspects of how a power system may be planned and operated to provide a reliable and economic supply of electrical energy. This includes the need to simulate generation production, particularly the appropriate coordination between thermal and hydro generation. One of the most difficult features of this is the incorporation of limited-energy pumped-storage hydro generation within such simulations. This paper describes a new approach for incorporating pumped-storage units using sequential Monte Carlo simulation. The scheduling is defined as a constrained optimisation problem using a network flow algorithm. The application and benefits of the proposed model are demonstrated using the IEEE reliability test system View full abstract»

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  • Power system frequency estimation

    Publication Year: 1998 , Page(s): 578 - 582
    Cited by:  Papers (20)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (476 KB)  

    A new algorithm of power system frequency estimation is presented. The algorithm applies orthogonal signal components obtained with use of two orthogonal FIR filters. The essential property of the algorithm presented is its outstanding immunity to both signal orthogonal component magnitudes and FIR filter gains variations which ensures 1.5 mHz accuracy of estimation over typical (±2 Hz) range of measured frequency deviation. The results of the algorithm simulation tests using the EMTP software package are also included. It was confirmed that the algorithm dynamics are good enough to track power system frequency even under transient conditions View full abstract»

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