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Generation, Transmission and Distribution, IEE Proceedings-

Issue 5 • Date Sep 1995

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Displaying Results 1 - 15 of 15
  • Conceptual design of air-core superconducting transformer for 500 kV cable transmission system

    Publication Year: 1995 , Page(s): 487 - 493
    Cited by:  Papers (4)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (420 KB)  

    The air-core superconducting transformer, which has a large magnetising current, has been proposed as a possible type of future power transformer having a function as a shunt reactor. In this paper, a basic design procedure for the air-core superconducting transformer is presented. By using this procedure, a 500/√3 kV-66/√3 kV-300 MVA single-phase air-core transformer which includes the function of a 100 MVA shunt reactor is designed. The size, weight, loss and capacity of this transformer are compared with those of a conventional transformer, and the performance of the designed air-core transformer in the model cable transmission system is analysed. From the results of these investigations, it is confirmed that the air-core superconducting transformer can function as a shunt reactor in addition to its principal function as a power transformer, and the merits of the air-core superconducting transformer are clarified View full abstract»

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  • Magnetic fields from transmission lines: comparison of calculations and measurements

    Publication Year: 1995 , Page(s): 481 - 486
    Cited by:  Papers (3)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (320 KB)  

    An experiment has been performed to compare the calculated and measured magnetic fields produced by a double-circuit 400 kV power transmission line. The phase currents were measured in the substation at one end of the line, taking particular care to measure the zero-sequence currents accurately, and the earth-wire current was measured at the span where the experiment was conducted. These currents were used to calculate the magnetic fields, using a number of computer programs based on Ampere's law. The magnetic field was measured at 22 positions ranging from 100 m on one side of the line to 500 m on the other side. Measured and calculated fields generally agreed well. The largest errors were ±7%±1 nT. These errors are attributed to a mixture of random errors in the calibration, resolution and synchronisation of the measuring instruments, and systematic errors stemming from the measurement of the zero-sequence currents View full abstract»

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  • Fuzzy neural networks for time-series forecasting of electric load

    Publication Year: 1995 , Page(s): 535 - 544
    Cited by:  Papers (7)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (608 KB)  

    Three computing models, based on the multilayer perceptron and capable of fuzzy classification of patterns, are presented. The first type of fuzzy neural network uses the membership values of the linguistic properties of the past load and weather parameters and the output of the network is defined as fuzzy-class-membership values of the forecast load. The backpropagation algorithm is used to train the network. The second and third types of fuzzy neural network are developed based on the fact that any fuzzy expert system can be represented in the form of a feedforward neural network. These two types of fuzzy-neural-network model can be trained to develop fuzzy-logic rules and find optimal input/output membership values. A hybrid learning algorithm consisting of unsupervised and supervised learning phases is used to train the two models. Extensive tests have been performed on two-years of utility data for generation of peak and average load profiles 24 hours and 168 hours ahead, and results for typical winter and summer months are given to confirm the effectiveness of the three models View full abstract»

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  • Co-ordinated multimachine PSS design using both speed and electric power

    Publication Year: 1995 , Page(s): 503 - 510
    Cited by:  Papers (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (440 KB)  

    The control signals required for supplementary stabilisation of interconnected multimachine power systems are simultaneously derived from Δω, ΔPe, the incremental speed and electrical power, respectively, of the machines concerned. Individual Δω and ΔPe stabilisers are designed and their outputs are mixed in appropriate proportions that are added to the corresponding machine terminal voltage reference to make the power system stable and robust. Appropriate weights for decentralised stabilisers are estimated using a parameterisation technique which assures adequate damping of all mechanical modes for each of the plants being controlled. As an illustration, the proposed method has been applied to a simulated single machine infinite bus and a multimachine system for performance evaluation View full abstract»

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  • Oscillatory interaction between synchronous generator and local voltage-dependent load

    Publication Year: 1995 , Page(s): 473 - 480
    Cited by:  Papers (4)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (588 KB)  

    The paper explores the influence of a voltage-dependent local load on electromechanical oscillations of a synchronous generator. The analysis is performed with different generator models, both with and without control devices. The classical static-load models were used as well as a generic model of dynamic load. It is shown that a voltage-dependent load can influence the damping of the electromechanical oscillations and thus the overall stability of the generator. This influence is very dependent on load parameters and on the generator's parameters and operating conditions. It is also shown that the use of dynamic-load models instead of static can have a significant influence on the evaluation of the total effect that voltage-dependent loads have on electromechanical oscillations of the generator View full abstract»

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  • Algorithm for determining phase-angle observability in the presence of line-current-magnitude measurements

    Publication Year: 1995 , Page(s): 453 - 458
    Cited by:  Papers (5)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (332 KB)  

    The paper presents an algorithm for the phase-angle observability of networks containing real power as well as line current magnitude measurements. It is assumed that all bus voltages are measured or known and the observability problem is solved only for the phase angles. The existence of line-current measurements creates the possibility of multiple solutions. Available methods of testing network observability cannot identify such multiple solutions. The algorithm described ensures that a unique solution for the phase angles exists for the given set of measurements. The algorithm is described in detail by using numerical examples View full abstract»

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  • Implicit generator and SVC modelling for contingency scheduling of reactive power dispatch

    Publication Year: 1995 , Page(s): 527 - 534
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (512 KB)  

    In the paper, CIGRE models of generating units are used for contingency scheduling of reactive power. These models are based upon the capability curves and the reactive power margin at each automatic voltage regulator (AVR) state (normal operation, threshold or loss of voltage control after AVR reaches the limits), rather than on the commonly used PV or PQ representation for generators in load flow. These models, in effect, add a supplementary generator node behind a reactance for each machine, which simulates the behaviour of the generator AVR at each state. The models are not detailed enough to allow the simulation of transient effects but are adequate to represent the system during a slow change under steady-state operation. The salient advantage of the proposed implicit method is to preserve the factorised triangulated nodal admittance matrix used for the fast decoupled load flow [B'] and [B"] for each state. This is achieved by calculating new injected powers and voltages at generating nodes and using these values for updating the solution during iteration for the final load-flow results. Simple illustrative cases for the explicit and implicit generation reactance modelling are presented. The injected power and voltage correction techniques are also used for static VAr compensator (SVC) representation, and a numerical example is given. The method was used for contingency analysis of a 620 busbar, 66 generating unit system. The technique proved to be reliable and efficient View full abstract»

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  • Multimachine power system stabiliser design based on new LQR approach

    Publication Year: 1995 , Page(s): 494 - 502
    Cited by:  Papers (11)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (548 KB)  

    The paper presents a novel systematic procedure for the design of excitation based stabilisers for large-scale interconnected electric power systems. The design method is based on newly obtained results in optimal linear quadratic regulator (LQR) design, and is superior to previously reported LQR approaches. A model of a five-machine interconnected power system which includes detailed representation of synchronous machines, excitation systems, turbines and speed governing mechanisms is considered. Stabilisers of structures are proposed. It is shown, through simulation studies, that the stabilisers improve the power system performance markedly, without excess demand for control action View full abstract»

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  • Security evaluation of composite power systems

    Publication Year: 1995 , Page(s): 511 - 516
    Cited by:  Papers (4)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (388 KB)  

    An approach to the security evaluation of a composite power system is proposed which uses probability techniques for quantitative power system reliability analysis. This approach incorporates both steady-state and transient-state considerations in the reliability evaluation of composite power systems View full abstract»

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  • Simplified bidirectional-feeder models for distribution-system calculations

    Publication Year: 1995 , Page(s): 459 - 467
    Cited by:  Papers (9)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (532 KB)  

    The paper presents three novel distribution-feeder models to simplify complicated distribution-system calculations. These equivalent models are developed to simulate the total series voltage drop at the end of the given feeder accurately, the total copper loss of the given feeder accurately, and a hybrid to simulate both voltage drop and feeder loss accurately. In addition, all of the proposed models are bidirectional. This means that power infeed can be at either end and the model is accurate. In contrast, unidirectional models previously developed are accurate only when power infeed is at the end specified by the model. This feature is important for a modern power-distribution system in which the power infeed of the switched feeder may change from one end to the other during service restoration or feeder reconfiguration. These bidirectional feeder models are illustrated by examples and applied to an actual feeder. The simulation results show that it is possible to reduce many complex feeders to simple equivalent models in the study of feeder-voltage profiles and losses with negligible error, even if the power infeeds of the given feeders are changed View full abstract»

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  • Simple wind farm dynamic model

    Publication Year: 1995 , Page(s): 545 - 548
    Cited by:  Papers (14)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (216 KB)  

    Contemporary fixed-speed wind turbines use induction generators rated at up to 500 kW, although turbines with ratings of over 1 MW are under development. A large wind farm may consist of up to 100 such turbines. The output power of each turbine fluctuates with its local incident wind and the position of the blades, so causing voltage disturbances on the public-supply network. A simple model has been developed to represent the induction generators, local power-factor-correction capacitors and network of a wind farm. This allows the variations in network voltage due to the changing aerodynamic torque of each turbine to be determined conveniently. The simple model has been compared to higher-order models and good agreement observed View full abstract»

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  • Iterative techniques for the solution of complex DC-rail-traction systems including regenerative braking

    Publication Year: 1995 , Page(s): 445 - 452
    Cited by:  Papers (4)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (624 KB)  

    The solution of simultaneous algebraic equations describing a DC-traction power system is based on an iterative technique because of their nonlinearity. Two iterative methods specified for DC-load-flow problems are described and their mathematical and geometrical explanations are presented. The methods have been tested for DC-fed traction power systems and comparisons made of the computational time and iteration count. The DC-traction software which has been developed enables the situation with trains operating in regenerative-braking mode to be simulated. A condition in which convergence problems are to be expected occurs when there is a surplus of power produced during regenerative braking. In this case two different modelling approaches to represent regenerative trains in the simulation are investigated. A representative DC-fed-traction power system with train regenerative braking was simulated and the preferred method is selected by analysing the simulation results obtained and the computation times expended View full abstract»

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  • Group-harmonic identification in power systems with nonstationary waveforms

    Publication Year: 1995 , Page(s): 517 - 522
    Cited by:  Papers (7)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (320 KB)  

    A strategy of `group-harmonic' identification is proposed for re-evaluating harmonic levels in power systems. The proposed strategy can relieve the problem of spectral leakage in the conventional application of the fast Fourier transform (FFT). Incorporating group-harmonic identification, the FFT algorithm can retain its efficiency for accurate harmonic calculations, especially for power systems with nonstationary waveforms View full abstract»

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  • Loss minimisation using islanding technique for district of Klang, Malaysia

    Publication Year: 1995 , Page(s): 523 - 526
    Cited by:  Papers (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (224 KB)  

    Distribution system loss reduction has been grossly neglected by most electricity utilities even though it contributes to no less than 75 per cent of the total system losses. Existing methods of loss reduction involve enormous capital cost and extensive rehabilitation to the existing distribution reticulation and are hence not very practical, compounded with the problem of coping with the high and dynamic load growth in most developing countries. The paper looks into techniques of selecting and operating the distribution system, with minimum or no physical change in the present distribution reticulation to reduce losses. It proposes that the existing distribution network be operated in `island groups' by paralleling selected feeders into an island View full abstract»

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  • Technical and economic feasibility of conversion to a higher voltage distribution

    Publication Year: 1995 , Page(s): 468 - 472
    Cited by:  Papers (2)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (372 KB)  

    The proper selection of the voltage level combinations when uprating voltages in an existing distribution system is very important as this would result in significant economic savings. The paper discusses the effects of high-voltage and distribution system primary voltage on the system characteristics and performance as practised in the Turkish system. It is shown that a higher primary distribution voltage minimises the investments on the high-voltage system and a completely new primary distribution system provided that it is accompanied by some means of feeder automation View full abstract»

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