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Generation, Transmission and Distribution, IEE Proceedings-

Issue 6 • Date Nov 1999

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Displaying Results 1 - 17 of 17
  • Improved ANN αth-order inverse TCSC controller for enhancing power system transient stability

    Page(s): 550 - 556
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (496 KB)  

    The paper focuses on studying an improved structure of ANN αth-order inverse, and its application as a TCSC controller in a real power system, consisting of 49 equivalent buses and 19 equivalent machines, to increase its transient stability. The ANN αth-order inverse, consisting of a single static ANN and a number of integrators, is used to eliminate the nonlinearities of the power system. An additional linear feedback controller is designed to enhance the stability of the linearised system. With almost the same structure (but different weights of ANN), this controller is first used to control a single-machine infinite-bus system and then the real multimachine system. The satisfactory simulation results show that such a control strategy has a promising future View full abstract»

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  • Innovative procedure for measurement of losses of transformers supplying nonsinusoidal loads

    Page(s): 617 - 625
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (704 KB)  

    The measurement of iron-core and copper losses of single-phase transformers is important in particular for transformers feeding nonlinear loads. A new digital data-acquisition method is devised for the separate measurement of iron-core and copper losses of transformers under any full or partial-load condition. The accuracy requirements of the instruments (voltage, current sensors, volt and current meters) employed are addressed. A 25 kVA, 7200/240 V single-phase transformer has been loaded with either three diode-bridge rectifiers and/or a thyristor-bridge rectifier at varying total harmonic voltage and current distortions, such that at the maximum permissible apparent power losses are identical to the rated losses. The maximum errors of losses are acceptably low if voltage (dividers) and current (shunts) sensors with 2% and digital instruments with 0.1% errors are used. The derating under nonlinear loads is measured as a function of dominant 3rd and 5th current harmonics. The influence of voltage distortion is studied. The total harmonic distortion of the current (THDi) was varied greatly from 0 to 90%, and the resulting voltage THDv values were below 6% for the given power system impedance. At large THDi values (e.g. 90%), the reduction in apparent power rating (RAPR) is not very large (≅10%). However, the real power capability (RPC) of the transformer is severely restricted: for example, at THDi =90% the RPC is about 0.5 pu. For this reason it might be advisable to define derating in terms of the reduction in real power capability and not in terms of RAPR View full abstract»

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  • Intelligent optical fibre monitoring of oil-filled circuit breakers

    Page(s): 557 - 562
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (572 KB)  

    Intelligent monitoring encompasses the extraction of information from data sets, which are only partially complete because of practical constraints on the deployment of measurement techniques. An experimental technique is described for monitoring a number of conditions within oil-filled circuit breakers from a single measurement method and using an optimised number of optical fibre sensing channels. The technique is based upon detecting changes in the optical intensity of light transmitted through the circuit breaker medium, using optical fibre delivery and capture at a number of different axial and radial locations within the circuit breaker chamber. It has been used during development testing at a short circuit test station for two oils with very similar physical characteristics but different kinematic viscosity as the arc extinguishing media. Results are presented which examine the dependence of the contact travel time upon arc duration and oil type. Quantitative information is given concerning the optical recovery time of the oil as a function of arc duration and axial location within the circuit breaker. The technique also detects the occurrence of fresh oil injection into the contact gap and enables the duration of its occurrence to be determined View full abstract»

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  • Two-phase neural network based solution technique for short term hydrothermal scheduling

    Page(s): 657 - 663
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (604 KB)  

    A two-phase neural network based optimisation method for short-term scheduling of a hydrothermal power system is proposed. The method is based on the solution of a set of differential equations obtained from transformation of an augmented Lagrangian energy function. A multireservoir cascaded hydroelectric system with a nonlinear power generation function of water discharge rate and storage volume is considered for implementation. The water transportation delay between cascaded reservoirs is taken into account. Results from this method are compared with those obtained from the augmented Lagrangian method. It is shown that the proposed solution technique is capable of yielding a good optimal solution with proper selection of control parameters View full abstract»

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  • Hierarchical dynamic state estimator using ANN-based dynamic load prediction

    Page(s): 541 - 549
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (736 KB)  

    The paper presents a new scheme for dynamic state estimation in power systems. The dynamics of the power system are modelled more realistically using artificial-neural-network-based bus-load prediction and load flow for state prediction. At the filtering step a hierarchical model which incorporates the measurement function nonlinearities is used. This considerably reduces the computational effort, making the proposed scheme suitable for on-line application. Test results for an IEEE 118-bus test system are presented to show the characteristics of the present method View full abstract»

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  • Methodology for simulating the response of nonlinear power circuits

    Page(s): 568 - 572
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (416 KB)  

    A technique is proposed for determining the responses of nonlinear power circuits. The technique involves connecting voltage sources such that the nonlinear circuit is separated into a linear part and a nonlinear part. Alternatively, current sources may be connected in series with the nonlinear elements. The mismatch currents flowing into the voltage sources (or the mismatch voltages across the current sources) are determined. The objective of the proposed technique is to determine the voltage (or current) sources for which the mismatch quantities are zero. The technique is general and can be applied to simulate transient and steady state responses View full abstract»

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  • Method for load-flow solution of radial distribution networks

    Page(s): 641 - 648
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (556 KB)  

    A simple and efficient method for solving radial distribution networks is presented. The proposed method involves only the evaluation of a simple algebraic expression of receiving-end voltages. Computationally, the proposed method is very efficient. The effectiveness of the proposed method is demonstrated through three examples View full abstract»

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  • Visualisation of voltage stability in large electric power systems

    Page(s): 573 - 576
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (532 KB)  

    Information technology offers much data from electric power systems that can be condensed into high-quality information with the techniques of computational intelligence to enable a precise assessment of the system's condition. A self-organising feature map (SOM) is used both for the indication and visualisation of voltage stability in large electric power systems. A conclusive mathematical description and selection of input data for the assessment of voltage stability is given. The application of a SOM is worked out bypassing the disadvantages of standard voltage stability indicators. The SOM is applicable to the analysis of power systems and the development of stabilising measures. The method is tested on a model of a real voltage-critical transmission system View full abstract»

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  • Robust damping of inter-area oscillations in power systems with superconducting magnetic energy storage devices

    Page(s): 633 - 639
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (496 KB)  

    The decentralised design of robust damping controllers is presented based on the linear matrix inequality (LMI) approach employing several superconducting magnetic energy storage (SMES) devices. These controllers are aimed at enhancing the damping of multiple inter-area modes in a large power system. The paper describes a comprehensive and systematic way of designing these controllers. Eigenvalue technique and nonlinear simulations further verify the robustness of the damping controllers for various operating conditions and load characteristics View full abstract»

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  • Reliability evaluation of substation control systems

    Page(s): 626 - 632
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (776 KB)  

    A technique to assess the reliability of substation control systems (SCSs) is demonstrated. The technique was developed as part of an ongoing project with National Grid Co. (NGC) that aims at quantitatively evaluating the merit of different approaches to substation control. Event trees are used to model the interdependency between the multiple functions (switchgear control, synchronising, indications, feeder autoreclosure, interlocking, etc.) present in a modern SCS. The event trees reflect the operating policies used by NGC in its transmission substations, but the applicability of the technique is not constrained by this. Hardware models of the computational equipment used in the SCS complement the functional models. The reliability indices chosen for this type of system and the reliability data used are discussed. The application of the technique is illustrated by an example and a sensitivity analysis is performed on the results View full abstract»

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  • Optimal reactive power dispatch using evolutionary computation: extended algorithms

    Page(s): 586 - 592
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (608 KB)  

    Extended evolutionary algorithms for solving the optimal reactive power dispatch are presented. In these approaches, based on evolutionary programming and evolution strategies, mutations in standard deviations have been controlled using a dynamic limits strategy. The proposals have been exhaustively analysed and compared with a state-of-the-art method. Good and reliable performance has been achieved and validation rests using the standard IEEE57 system are reported View full abstract»

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  • Knowledge-based neural network for voltage contingency selection and ranking

    Page(s): 649 - 656
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (680 KB)  

    Voltage contingency screening and ranking is performed to choose the contingencies that cause the worst voltage problems. A knowledge-based conceptual neural network (KBCNN) is developed for fast voltage contingency selection and ranking. A recognised shortcoming of the ANN based approach is that the problem solving knowledge of ANN is represented in the connection weights, and hence is difficult for a human user to comprehend. One way to provide an understanding of the behaviour of neural networks is to extract rules that can be provided to the users. The rules extracted are used to build a knowledge-based connectionist network for learning and revision of rules. The knowledge-based neural network is applied for voltage contingency selection and ranking in an IEEE 30-bus system and a practical 75-bus Indian system. Once trained, the KBCNN gives accurate selection and ranking for unknown patterns. At the same time, the system user is able to validate the output of the ANN under all possible input conditions. The system user is provided with the capability to determine the set of conditions under which a line-voltage is critical, and if critical, then how severe it is, thereby providing some degree of transparency of the ANN solution View full abstract»

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  • Advanced constrained genetic algorithm load flow method

    Page(s): 609 - 616
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (740 KB)  

    An efficient and reliable constrained genetic algorithm based load flow algorithm is developed. The components and the constraint satisfaction methods in the algorithm are presented. A nodal voltage differential technique and a gradient method are developed to accelerate the solution process in the algorithm. A method for dealing with generator reactive power limits is also developed. The new algorithm can detemine multiple load flow solutions and can be used to determine the loadability limits of transmission systems. Its power is demonstrated through its applications to evaluate the loadability of the IEEE 30-, 57- and 118-node systems. Detailed results on the 30-node system are presented View full abstract»

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  • Improvements in the performance of self-excited induction generator through series compensation

    Page(s): 602 - 608
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (484 KB)  

    Improvements in the performance of a three-phase self-excited induction generator (SEIG) through series compensation are investigated. Both methods, namely short-shunt and long-shunt configurations, of capacitive series compensation for the SEIG are analysed and compared for the selection of capacitive elements. Computed results are compared with experimental results for resistive and inductive loads to verify the developed algorithm and design of such a system View full abstract»

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  • Network reconfiguration for load balancing in distribution networks

    Page(s): 563 - 567
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (468 KB)  

    Network reconfiguration of a power distribution system is an operation to alter the topological structure of distribution feeders by changing open/closed status of sectionalising and tie switches. By transferring loads from the heavily loaded feeders to the lightly loaded ones, network reconfiguration can balance feeder loads and alleviate overload conditions of a network. A general formulation of the network reconfiguration for load balancing is given for the optimal balancing of loads in distribution network and a solution approach is presented. The solution employs a search over different radial configurations, created by considering branch-exchange type switches. The proposed algorithm, called distance measurement technique (DMT) has been developed based on the two-stage solution methodology. The first stage finds a loop, which gives the maximum improvement in load balancing in the network. In the second stage, a switching option is determined in that loop to obtain maximum improvement in load balancing. The DMT employs a graphical method in which different circles are drawn and the distances of various points from the centre of the loop circle are computed to achieve the optimal or near optimal configuration for load balancing. The solution algorithm of the proposed method can identify the most effective branch-exchange operations for load balancing with minimum computational effort. The algorithm has been tested with promising results on a 69-bus radial distribution system View full abstract»

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  • Comparison of touch and step voltages between IEEE Std 80 and IEC 479-1

    Page(s): 593 - 601
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (612 KB)  

    A comparison of the safety criteria of two widely accepted standards, i.e. the IEEE Std 80 and the IEC 479-1 is proposed. The two standards differ in their definitions of permissible body current and body resistance. Another difference is that the IEC 479-1 does not provide guidance on human feet/soil contact impedances. It tacitly assumes that these impedances are computable by the designer. A comprehensive study of permissible touch and step voltages by these two standards is included for a wide range of conditions, which enables a direct comparison of the two standards. It is shown that differences exist and these differences are quantified View full abstract»

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  • Learning-coordinate fuzzy logic control of dynamic quadrature boosters in multi-machine power systems

    Page(s): 577 - 584
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (768 KB)  

    A learning-coordinated fuzzy logic control (LCFLC) strategy is investigated for the control of dynamic quadrature boosters (DQBs) installed distributively in a large-scale power system to enhance the power system stability. In this strategy a reinforcement learning technique is employed to search for optimal parameters of the fuzzy logic controllers according to a given performance index, to control the DQBs in a coordinated fashion. A simulation study is undertaken in a thirteen-machine power system. The simulation results show that the LCFLC can be used as an online control strategy to give coordination of the locally installed DQBs to improve the power system stability View full abstract»

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