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Generation, Transmission and Distribution, IEE Proceedings-

Issue 5 • Date Sep 1996

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Displaying Results 1 - 19 of 19
  • Robust decentralised load-frequency control of multi-area power systems

    Page(s): 377 - 386
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (616 KB)  

    A robust decentralised load-frequency controller, based on the Riccati-equation approach, is proposed for multi-area power systems with parametric uncertainties. It comprises N local robust load-frequency controllers for a N-area power system. N interlinked Riccati equations are produced initially which are separated via a decoupling technique. Bounds of system parametric uncertainties are included in these Riccati equations to improve the robustness of the intended controller. One local robust load-frequency relationship is obtained by solving the corresponding decoupled Riccati equation. It operates on its local measurements; feedback from other areas is not needed. The overall system is asymptotically stable, for all admissible system parametric uncertainties, when all the local load-frequency controllers are working together. Good performance is reported from the studied three-area power system even in the presence of the generation-rate constraint View full abstract»

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  • Novel method of finding the first swing stability margin of a power system from time domain simulation

    Page(s): 413 - 419
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (564 KB)  

    A novel method of determining the first swing stability margin of a power system is presented by directly analysing the output results of the conventional time domain simulation method. Unlike hybrid methods, the proposed method does not use the concept of the transient energy function method in finding the stability margin. This avoids the computation of pseudo fault-on trajectory or line search and also eliminates the additional computational burden and modelling limitations associated with the transient energy function method. For a stable system, the proposed method determines the stability margin from the decelerating power of the severely disturbed machines when their post-fault angle reaches the peak values. For an unstable situation, the instability margin is determined from the minimum post-fault speed of the unstable machines. The method is very simple to implement and requires only the time response of machine angles and speeds. The proposed method was successfully applied to the CIGRE and Iowa systems for a number of fault conditions View full abstract»

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  • Robust nonlinear controller for power system transient stability enhancement with voltage regulation

    Page(s): 407 - 412
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (492 KB)  

    A new robust nonlinear controller that has the ability to enhance the transient stability and achieve voltage regulation simultaneously via excitation control for power systems is proposed. The structure of the controller is to add a proportional plus integral (PI) type voltage servo-compensator to the existing direct feedback linearisation (DFL) controller; a design procedure is proposed to guarantee the stability of the closed loop system in a possible working region. By using this robust nonlinear controller, direct measurement of the power angle for stabilising feedback control and calculation of the target power angle for voltage regulation are not necessary when employing the feedback linearisation technique. Performance analysis and simulation on a single-machine infinite-bus power system show that the proposed controller can retain the characteristic of the DFL controller and thus can enhance the transient stability as well as achieve voltage regulation of the power system View full abstract»

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  • Line monitoring and fault location using spread spectrum on power line carrier

    Page(s): 427 - 434
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (776 KB)  

    Signals transmitted over the power line carrier system are used to locate faults and other impedance mismatches on EHV power lines. The compatibility and sensitivity performance requirements for doing this are summarised. Conventional remote sensing waveshapes are reviewed and direct-sequence spread-spectrum modulation is proposed for this application. Optimal signal processing techniques are outlined and frequency domain correlation techniques are detailed. Prototype hardware has been constructed and on-line results are presented for a 225 km 330 kV line. Line reflections were identified within accuracy of 1.6 km even though the channel bandwidth was limited to 50 kHz by external constraints. It is shown that accuracy is dependent on channel bandwidth, signal-to-noise ratio and waveform energy. It is suggested that a further increase in accuracy is possible by referencing the received signal to known impedance discontinuities such as the transpositions. Fault location accuracy down to one span should be possible using this technique, which will work on both energised and de-energised lines View full abstract»

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  • Numerical and experimental evaluation of magnetic field generated by power busbar systems

    Page(s): 455 - 460
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (452 KB)  

    The paper presents a hybrid finite element-boundary element formulation which has been applied to the analysis of a four conductor device under AC supply, also considering the presence of shields. The system impedance matrix and the magnetic field predicted by the model have been compared with the experimental outcomes. The model predictions are found to be in very good agreement with measurements. Finally, it is shown that the use of only the finite element method is inadequate for a correct estimation of the external magnetic field View full abstract»

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  • Intelligent control of large power transformer cooling pumps

    Page(s): 474 - 478
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (452 KB)  

    The paper describes a novel approach to the control of large power transformer cooling. An intelligent controller is proposed by taking elements of fuzzy logic and neural networks, together with recent advances in sensor technologies. This controller drives the cooling system to operate in flow and temperature regimes which limit the problem of streaming electrification while minimising thermal degradation of the insulation. A simplified example is given to demonstrate the viability of the proposed controller View full abstract»

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  • Nonlinear autoregressive integrated neural network model for short-term load forecasting

    Page(s): 500 - 506
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (604 KB)  

    A novel neural network technique for electric load forecasting based on weather compensation is presented. The proposed method is a nonlinear generalisation of the Box and Jenkins approach for nonstationary time-series prediction. A nonlinear autoregressive integrated (NARI) model is identified to be the most appropriate model to include the weather compensation in short-term electric load forecasting. A weather compensation neural network based on a NARI model is implemented for one-day ahead electric load forecasting. This weather compensation neural network can accurately predict the change of electric load consumption of the coming day. The results, based on Hong Kong Island historical load demand, indicate that this methodology is capable of providing a more accurate load forecast with a 0.9% reduction in forecast error View full abstract»

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  • Stochastic evaluation of turbine-generator shaft torsional torques during faulty synchronisation

    Page(s): 487 - 491
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (460 KB)  

    A probabilistic approach to the evaluation of the maximum torsional torques induced in turbine-generator shafts during faulty synchronisation is presented. This approach is based on utilisation of the conditional probability theorem to assess these torques. In this context, investigations have been conducted on a large turbine-generator model taking into consideration the uncertainty of several factors associated with the practical operation of a power system. The results of these investigations are presented in the form of discrete probability distributions of the maximum torsional torques induced in the turbine-generator shaft sections View full abstract»

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  • Constrained multiobjective global optimisation of longitudinal interconnected power system by genetic algorithm

    Page(s): 435 - 446
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (912 KB)  

    A genetic-based algorithm is proposed to solve the multiobjective global optimisation problem of a longitudinal interconnected power system, which incorporates various constraints during the optimisation of dispatch solution with two objectives in mind: economic and environmental requirements. Its effectiveness is verified through a three-area test system with multiple fuels and multiple pollutants. Consequently, the results of the sample system are analysed to demonstrate the internal relationships among various constraints and objectives View full abstract»

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  • Computational method for remote meter calibration in power systems

    Page(s): 393 - 398
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (552 KB)  

    Measuring instruments in a power system are numbered in thousands and are dispersed geographically. The readings of those instruments are telemetered to the control centre and then used in a power system state estimation program for further processing. Field technicians calibrate these instruments routinely at great cost. The purpose of remote meter calibration is to determine, using analytical methods in the control centre, which instrument needs calibration and to estimate the calibration error. Results of many runs of the power system state estimation program are used to demonstrate the feasibility of remote meter calibration in a power system. The IEEE 14-bus test system is used for the testing. It is shown that the simulated fixed (calibration) errors in all types of power system measurements can be advantageously estimated View full abstract»

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  • Application of Gabor transform technique to supervise power system transient harmonics

    Page(s): 461 - 466
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (424 KB)  

    A novel approach to visualising power system harmonic trends is proposed. The Gabor transform technique, embedded with a Gaussian-like window function, is applied to help monitor harmonic variations in the time dimension. Using the proposed scheme, power system transient harmonics can be closely observed. The proposed method has been tested for the inspection of inrush current harmonics of transformers and industrial arc furnace disturbances. The results demonstrate the merits of the proposed method for the applications View full abstract»

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  • New scaling concept in power system analysis

    Page(s): 399 - 406
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (816 KB)  

    Three standard methods which are usually applied for scaling of AC power system models are analysed in the paper: the PU method, the percentage method (P% method) and the SU method (scaling to a unique voltage level). Several theoretical and practical problems of these methods are identified: 1) the PU method is not in full accordance with both formalisms and terminology inherent to distribution practice; 2) applications of both the P% and SU methods are not suitable for elaboration of power system issues; and 3) application of the PU method is not suitable for calculation of the most complex power system (quasi) steady states treated in the sequence domain. These shortcomings are sufficient reason for redefining the standard scaling methods. The redefinition is performed in two steps: 1) standard scaling methods are extended, redefined and synthesised by a new (generalised) scaling concept; and 2) this concept is generalised for elaboration of power system models in the sequence domain. The above mentioned three problems are solved by the new scaling concept. This concept is demonstrated by several representative examples View full abstract»

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  • Self-tuning control applied to turbogenerator AVRs

    Page(s): 492 - 499
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (768 KB)  

    Results from a research and development programme devoted to turbogenerator control are described. Digital self-tuning controllers are covered, although fixed parameter controllers have also been considered. Simulations and tests on laboratory scale machines have been accomplished successfully, with a prototype self-tuning controller being manufactured. A set of typical results is given, covering responses to normal set point changes and fault dynamics. These new controllers are shown to have good potential for practical application View full abstract»

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  • Enhanced adequacy equivalent for composite power system reliability evaluation

    Page(s): 420 - 426
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (552 KB)  

    The paper presents a technique for studying the adequacy of a selected area in a power network in which the remaining network is modelled as an adequacy equivalent. This approach can be very useful for evaluation of large composite power systems as it is often necessary in practice to perform adequacy analysis of selected relatively small regions in the network. It is useful in conducting adequacy studies of interconnected areas where one area can be replaced by its equivalent, thus reducing the size of the overall system. The paper presents a new approach and shows that annual adequacy indices can be efficiently calculated using this technique, leading to greatly decreased computation times View full abstract»

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  • Generation availability assessment of wind farms

    Page(s): 507 - 518
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1072 KB)  

    Wind generation is one of the most successful sources of renewable energy for the production of electrical energy. As the number of installations connected into existing networks grows rapidly worldwide there is a need to study the reliability of these energy sources and assess their effects on the system. However, the technical characteristics of wind generation make existing conventional generation models not directly applicable. A new probabilistic model of a wind farm to be used in reliability studies is presented. This model considers the stochastic nature of wind, the failure and repair processes of the wind turbines under different wind regimes, and the output characteristics of the wind turbine in detail. Spatial wind speed correlation and waking effects can also be considered. The model can be used with one or several types of wind turbines. Analytical techniques are used. A practical application of the models is also included View full abstract»

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  • Loss-constrained economic power dispatch

    Page(s): 387 - 392
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (416 KB)  

    A new P-dispatch module for the decomposed optimal power flow method is presented by which undesired increases in transmission losses are prevented via an additional constraint imposed upon the module. The constraint only requires the restriction of the final updates of the control variables and therefore neither destroys the form of optimisation equations nor requires extra considerable calculation time. However, it provides flexibility in the choice of handling either the minimum cost or the minimum loss problem. The effectiveness of the method is demonstrated by applying it to two sample networks View full abstract»

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  • Newton-Raphson algorithm for the reliable solution of large power networks with embedded FACTS devices

    Page(s): 447 - 454
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (700 KB)  

    A new and efficient algorithm for the reliable load flow solution of power network branches controlled by flexible AC transmission systems (FACTS) is presented. General admittance-based models are given for series compensators, phase-shifters and tap-changers. Their inclusion in a Newton-Raphson load flow exhibiting quadratic convergence is described and the prowess of the algorithm is demonstrated by comparison with production-grade load programs where the state variables of controllable devices are updated at the end of each Newton-Raphson iteration. Control coordination and initialisation strategies for the controlled branches and nodes have been thoroughly investigated View full abstract»

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  • Torsional fatigue of turbine-generator shafts owing to network faults

    Page(s): 479 - 486
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (584 KB)  

    Many studies have been made of the fatigue processes resulting from cyclic stress which the metal for making turbine generator shafts has to bear. In the paper, a modified dynamic computer program, written on the basis of these theories, is used to simulate the shaft torsional vibrations resulting from four types of power network fault. The purpose is to study the influence of a safety factor, selected in the first stage of design, on the damage accumulated following worst-case fault clearance and synchronising of the simulated machines View full abstract»

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  • Rule-based approach to load transfer to alternate supplies based on the phase of the residual voltage on the disconnected busbar

    Page(s): 467 - 473
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (668 KB)  

    Transfer techniques and a rule-based approach to an in-phase load transfer scheme for secondary selective substations are developed. The transfer scheme, with its developed transfer techniques and rule based algorithm, integrates into a microcontroller-based in-phase transfer controller to maintain the continuity of power supply to process loads. The rule sets initiating conditions, blocking transfer criteria, load shedding schedules and possible events. It provides a safe and successful bus transfer system. Operations of the load transfer scheme with simulated load conditions have been tested through the the in-phase transfer controller. The results of computer simulation and test measurements show that the load transfer operation is performed successfully. The inrush current, transient torque and service reliability can also be improved by using this transfer scheme View full abstract»

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