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Volume 147
Issue 4
IEE Proceedings - Generation, Transmission and Distribution
Volume 147, Issue 4, July 2000
Volumes & issues:
Volume 147, Issue 4
July 2000
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- Author(s): D.A. Koppikar ; S.V. Kulkarni ; J. Turowski
- Source: IEE Proceedings - Generation, Transmission and Distribution, Volume 147, Issue 4, p. 197 –201
- DOI: 10.1049/ip-gtd:20000435
- Type: Article
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p.
197
–201
(5)
Contemporary power transformers are very important components of power systems from the points of view of both reliability and energy saving. Their complicated three-dimensional (3-D) structure, leakage-field region with solid nonlinear steel elements and screen/shunt system should be modelled, calculated and designed using 3-D fast, interactive programs. After examination of many known methods it was concluded that only the 3-D reluctance-network method (RNM-3D) fulfils the needs of designers, namely simple, fast, low cost, easy to use and understand, and giving effective integral-field, power and hotspot output data. Following a short discussion of the principles of such a dedicated 3-D package for power transformers, the satisfactory industrial verification of the method is carried out on six medium and large transformers from 31.5 to 315 MVA. - Author(s): J.-H. Teng
- Source: IEE Proceedings - Generation, Transmission and Distribution, Volume 147, Issue 4, p. 202 –206
- DOI: 10.1049/ip-gtd:20000512
- Type: Article
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p.
202
–206
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A framework for handling current magnitude measurements for both transmission and distribution system state estimation is given. A fast-decoupled formulation is developed to enhance both computation time and storage requirement. This method is based on the equivalent current measurements, the rectangular co-ordinates and the weighted least square approach. Tests have shown that the proposed method can outperform other formulations in handling the current magnitude measurements. - Author(s): C.L. Masters ; J. Mutale ; G. Strbac ; S. Curcic ; N. Jenkins
- Source: IEE Proceedings - Generation, Transmission and Distribution, Volume 147, Issue 4, p. 207 –212
- DOI: 10.1049/ip-gtd:20000410
- Type: Article
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p.
207
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The commercial viability of wind-driven embedded renewable generation (ERG) projects is sensitive to connection costs. These costs vary with the voltage level at which the ERG is connected; generally the higher the voltage, the higher the cost. Windfarm developers of ERG therefore prefer to connect at lower voltages. However, because distribution networks are normally limited by permissible voltage fluctuations rather than by thermal considerations, network operators prefer to connect ERG at higher voltages where their overall impact on voltage profiles is minimal. This conflict of objectives between ERG developers and network operators is usually settled through simple deterministic load flow studies, usually based on one critical case representing conditions of minimum load and maximum ERG output. Such studies only consider extreme events and do not take into account the likelihood of these events occurring. However, new European standards describe voltage characteristics in statistical terms. Although these standards are not intended for use in assessing the level of penetration of ERG, they point to statistical and probabilistic approaches as the way forward in such assessments. This is particularly important for wind generation because of its stochastic output. Two simple wind speed models based on the Markov modelling technique are presented, which may be used to evaluate the impact of windfarms. The models give satisfactory results when applied to the evaluation of voltage profiles in distribution networks. The probability density function of voltage can be obtained and used in assessing the level of ERG that might be accepted on an existing network. A 281-node generic distribution system model based on a real network is used to illustrate the application of the proposed models. - Author(s): A.A. El Desouky and M.M. El Kateb
- Source: IEE Proceedings - Generation, Transmission and Distribution, Volume 147, Issue 4, p. 213 –217
- DOI: 10.1049/ip-gtd:20000521
- Type: Article
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p.
213
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Different neural-network configurations with an adaptive learning algorithm are designed for prediction of monthly load demand. The importance of the load forecast for Jeddah city, Saudi Arabia, is considered to justify development of new hybrid adaptive techniques. The techniques utilise the available nine years' information for both load and temperature. The first seven years' data are used for training the artificial neural network (ANN) while the performance of the ANN is verified from the forecast of two years ahead and then comparing with the true last two years' data. As the trend of the load is an important factor, several methods of extracting the load-demand trend have been examined to ensure the enhancement in forecast accuracy. Different network learning cases are pursued using ANN and a hybrid ARIMA/ANN to arrive at a suitable model. The results of both the ANN and the hybrid ARIMA/ANN forecasting were most promising compared with corresponding forecasts produced using the established time-series method. - Author(s): M.H. Haque
- Source: IEE Proceedings - Generation, Transmission and Distribution, Volume 147, Issue 4, p. 218 –222
- DOI: 10.1049/ip-gtd:20000412
- Type: Article
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p.
218
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FACTS devices are now recognised as a viable solution for controlling transmission voltage, power flow, dynamic response, etc. and represent a new era for transmission systems. It has been proved that the centre or midpoint of a transmission line is the optimal location for shunt FACTS devices or reactive power support and the proof is based on the simplified line model. The validity of the above optimal location of shunt FACTS devices is investigated, when the actual model of the line is considered. It is found that the FACTS device needs to be placed slightly off-centre to get the highest possible benefit. Both the power transfer capability and stability of the system can further be improved if the shunt FACTS device is placed at the new optimal point instead of at the midpoint of a line having some resistance. This finding contradicts the previous results found for the simplified line model. - Author(s): C.Y. Chung ; C.T. Tse ; K.W. Wang ; A.K. David ; C.W. Yu
- Source: IEE Proceedings - Generation, Transmission and Distribution, Volume 147, Issue 4, p. 223 –230
- DOI: 10.1049/ip-gtd:20000444
- Type: Article
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p.
223
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Traditionally, a lead/lag circuit is regarded as providing phase compensation for a controller, so a few lead/lag stages would be needed to achieve sufficient phase shifts at the frequency of concern. A different viewpoint is offered as a basis of the SVC damping controller design. From time constant synthesis, three different objectives of a properly designed lead/lag circuit are highlighted, but the dominant one is associated with gain compensation, rather than phase compensation. Moreover, the required number of stages, the choice of lead or lag compensation, and the selection of the time setting ranges are all indicated from the synthesis. - Author(s): E. Viel and H. Griffiths
- Source: IEE Proceedings - Generation, Transmission and Distribution, Volume 147, Issue 4, p. 231 –238
- DOI: 10.1049/ip-gtd:20000404
- Type: Article
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p.
231
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An advanced analytical model is presented for the evaluation of ground return currents at substations fed by both three and single-core cable circuits. The circuit model includes the accurate treatment of an intermediate substation between the source and the faulted substation, unlike Engineering Recommendation EA S.34, which adopts a more simplified approach. Through detailed parametric studies, the differences between the simplified and the more accurate treatment are quantified. The effects that variations in the key parameters — cable length and type, substation earth impedances — have on the magnitude of the ground return current are identified and explained. - Author(s): R.A. Jabr and A.H. Coonick
- Source: IEE Proceedings - Generation, Transmission and Distribution, Volume 147, Issue 4, p. 239 –244
- DOI: 10.1049/ip-gtd:20000437
- Type: Article
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p.
239
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A method for solving the active power economic dispatch problem is presented. The problem is formulated as a convex program which allows the inclusion of a second-order network model, phase shifters and operational constraints. An accurate representation of the line losses is achieved through the second-order model. The problem is solved using a homogeneous interior point (HIP) algorithm. The HIP algorithm yields either an approximate global optimum or detects the possible infeasibility or unboundedness of the problem. Moreover, this algorithm does not require any skill for setting a proper starting point. The algorithm is tested on standard IEEE networks and on a practical network. Computational experience shows that the method is efficient. - Author(s): Q. Lu ; S. Mei ; W. Hu ; Y.H. Song ; M. Goto ; H. Konishi
- Source: IEE Proceedings - Generation, Transmission and Distribution, Volume 147, Issue 4, p. 245 –251
- DOI: 10.1049/ip-gtd:20000441
- Type: Article
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p.
245
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Based on a combination of regulation linearisation and H∞ theory, a novel nonlinear robust optimal excitation control for multimachine power systems is presented. The feedback variables of the derived control law are completely local measurements. Simulations performed on a 6-machine system demonstrate that the proposed nonlinear H∞ excitation controller is more effective than other types of excitation controllers for improving both dynamic performance and the stability of power systems suffering from large disturbances. In addition, the H∞ control for a regulation linearisation system is equivalent to a nonlinear H∞ control for the original nonlinear control system in the sense of a type of L2-gain. - Author(s): H.S. Gill ; T.S. Sidhu ; M.S. Sachdev
- Source: IEE Proceedings - Generation, Transmission and Distribution, Volume 147, Issue 4, p. 252 –260
- DOI: 10.1049/ip-gtd:20000505
- Type: Article
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p.
252
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The design, implementation and testing of a microprocessor-based busbar protection system is presented. The proposed system employs a protection technique that uses the positive- and negative-sequence models of the power system. The system is composed of delta-impedance relays which implement a fault-detection algorithm, based on the developed technique. The algorithm, hardware and software of the relays are described. Performance of the proposed system was checked in the laboratory; the testing procedure and test results are presented. - Author(s): R.-H. Liang and C.-C. Cheng
- Source: IEE Proceedings - Generation, Transmission and Distribution, Volume 147, Issue 4, p. 261 –266
- DOI: 10.1049/ip-gtd:20000507
- Type: Article
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p.
261
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Accurate load forecasting is of great importance for power system operation; it is the basis of economic dispatch, unit commitment, hydrothermal coordination, and system security analysis, among other functions. An approach based on combined regression method and fuzzy inference system is developed for short-term load forecasting. The multilinear regression model is applied to find a preliminary load forecast. In addition, the fuzzy inference system makes a load correction inference from historical information and past forecast load errors from a multilinear regression model to infer a forecast load error. Adding the inferred load error to the preliminary load forecast obtains a final forecast load. The effectiveness of the proposed approach to the short-term load forecasting problem is demonstrated by practical data from the Taiwan Power Company.
Fast 3-dimensional interactive computation of stray field and losses in asymmetric transformers
Handling current-magnitude measurement in transmission and distribution system state estimator
Statistical evaluation of voltages in distribution systems with embedded wind generation
Hybrid adaptive techniques for electric-load forecast using ANN and ARIMA
New optimal location of shunt FACTS devices in long transmission lines
Synthesis of sensitivity coefficients for controller parameters of static var compensator
Fault current distribution in HV cable systems
Homogeneous interior point method for constrained power scheduling
Decentralised nonlinear H∞ excitation control based on regulation linearisation
Microprocessor-based busbar protection system
Combined regression-fuzzy approach for short-term load forecasting
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