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Volume 144
Issue 5
IEE Proceedings - Generation, Transmission and Distribution
Volume 144, Issue 5, September 1997
Volumes & issues:
Volume 144, Issue 5
September 1997
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- Author(s): S. Ćurčić ; C.S. Özveren ; K.L. Lo
- Source: IEE Proceedings - Generation, Transmission and Distribution, Volume 144, Issue 5, p. 389 –398
- DOI: 10.1049/ip-gtd:19971355
- Type: Article
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p.
389
–398
(10)
Electric power distribution network restoration is an emergency activity in system control, a real-time environment. It takes place when the basic function of the electric utilities, to supply customers, fails due to faults in the network. Restoration of supply to the affected customers can be a large-scale combinatorial problem with the control operators under pressure to find a restoration solution and implement it as quickly as possible. Therefore, they need an effective computer-based restoration solution to aid them. The paper describes a modular restoration strategy designed to deal with realistic, large-scale outages caused by faults of any type in HV and MV distribution networks. It is based on heuristic search guided by expert knowledge. In searching for a restoration solution the strategy utilises the available spare loading capacity of both the HV and the MV networks as necessary. The algorithm observes the loading constraint in discrete time resulting in more affected load demand supplied in the case of partial restoration and a smaller number of switching operations in the general case. By giving preference to remotely operated switching devices over manually operated switching devices it brings about fast implementation of a restoration scenario. In the case of partial restoration it restores important customers with priority. To do that more efficiently, it considers a hierarchy of the important customers. The proposed restoration strategy can be an effective aid to control operators, however it is also an effective tool in training and in establishing network reconfigurations for maintenance work and in assisting system security analyses. - Author(s): J.W. Bialek
- Source: IEE Proceedings - Generation, Transmission and Distribution, Volume 144, Issue 5, p. 399 –405
- DOI: 10.1049/ip-gtd:19971386
- Type: Article
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p.
399
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(7)
The paper analyses problems associated with the merchandise surplus (i.e. the difference between payments and revenues that is inherent to the spot pricing for electricity). A novel method of pricing is proposed which does not alter the optimal prices faced by the generators but makes the price faced by the loads equal to the weighted average of the nodal optimal prices with the weights equal to power notionally supplied to a given load from individual generators. This averaging, which is based on a recently proposed electricity tracing method, eliminates the merchandise surplus and most of the problems associated with it. The paper also suggests a hedging mechanism which not only separates financial performance of the generators and the loads from the actual operation but also places a financial incentive for the independent system operator to operate the system in such a way as to minimise the cost of transmission. Application of the method has been illustrated using a sample 10-node CIGRE network. - Author(s): C.S. Chang ; J.M. Chen ; D. Srinivasan ; F.S. Wen ; A.C. Liew
- Source: IEE Proceedings - Generation, Transmission and Distribution, Volume 144, Issue 5, p. 406 –414
- DOI: 10.1049/ip-gtd:19971278
- Type: Article
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p.
406
–414
(9)
Great emphasis has been put on applying expert systems for transmission system fault diagnosis. However, very few papers deal with the unavoidable uncertainties that occur during operation involving the fault location and other available information. The paper proposes a method using fuzzy sets to cope with such uncertainties. A fuzzy expert system is developed, which requires much less memory to store an active database than that used by conventional rule-based expert systems. The fuzzy expert system identifies two basic network section sets, Shealthy for the healthy subnetwork and Sisland for the fault islands, using the postfault status of circuit breakers and relays. It then conducts inference to determine the most likely fault sections and the associated fault sequences. Two case studies are provided to demonstrate salient features of the proposed approach, and to compare results both with a conventional rule-based expert system and a refined genetic algorithm. The proposed fuzzy expert system can be operated either in a stand-alone manner, or as part of the overall architecture of a diagnosis system for parallel decision making. - Author(s): A.T. Sarić ; M.S. Ćalović ; M.B. Djukanović
- Source: IEE Proceedings - Generation, Transmission and Distribution, Volume 144, Issue 5, p. 415 –422
- DOI: 10.1049/ip-gtd:19971490
- Type: Article
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p.
415
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(8)
To reach an optimal size, location and commitment schedule of shunt capacitors on a yearly based operations planning interval under the fuzzy environment, a fuzzy set theory based multistage optimisation is developed, where the loads, source voltage and objective function are all expressed in fuzzy set notations. To verify its effectiveness, the proposed approach is applied to a real distribution system. Results from the simulation show the advantages of this approach over the conventional crisp shunt capacitors compensation method in radial distribution systems. This provides good prospects for its application in practical distribution system compensation problems in an environment of uncertainty and vagueness. - Author(s): R.W. Ferrero and S.M. Shahidehpour
- Source: IEE Proceedings - Generation, Transmission and Distribution, Volume 144, Issue 5, p. 423 –428
- DOI: 10.1049/ip-gtd:19971382
- Type: Article
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p.
423
–428
(6)
In deregulated systems, utilities have partial knowledge of the price and amount of power available in the market. Other variables such as forecasted load in utility and fuel availability may also be uncertain. In the paper, an optimisation procedure that models uncertainties using fuzzy numbers is presented. The proposed method defines the range of control variables (local generations and imports) for satsifying operational constraints with a total operation cost lower than a predefined goal. Price of imported power, local generation as well as line flows and loads are defined as linguistic variables and represented with fuzzy numbers. The fuzzy optimisation is transformed into a classical (crisp) optimisation problem by considering a degree of acceptance for each constraint. The problem is formulated with a linear objective function and nonlinear constraints. An iterative procedure is used to compute the minimum operation cost. An example system is used to show applications of the proposed method in the decision-making process inherent in uncertain environments. - Author(s): K.L. Butler ; J.A. Momoh ; D.J. Sobajic
- Source: IEE Proceedings - Generation, Transmission and Distribution, Volume 144, Issue 5, p. 429 –436
- DOI: 10.1049/ip-gtd:19971433
- Type: Article
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p.
429
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(8)
The paper discusses results of studies performed on a new fault-diagnosis method for distribution systems using acquired field data. The effectiveness of the fault-diagnosis method in distinguishing between faulted conditions and system conditions that appear fault-like is demonstrated, for a field-test system, using data recorded at two utility distribution systems. The new method uses two major components: a signal preprocessor and a novel supervised clustering-based neural network which perform fault detection in the presence of arcing, classification of the fault type and preliminary fault location through the identification of the faulted phase. The work represents the first time that a supervised clustering neural network has been used for distribution fault diagnosis. - Author(s): C.R. Fuerte-Esquivel and E. Acha
- Source: IEE Proceedings - Generation, Transmission and Distribution, Volume 144, Issue 5, p. 437 –444
- DOI: 10.1049/ip-gtd:19971385
- Type: Article
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p.
437
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(8)
A new and comprehensive load flow model for the unified power flow controller (UPFC) is presented. The UPFC model is incorporated into an existing FACTS Newton–Raphson load flow algorithm. Critical comparisons are made against existing UPFC models, which show the newly developed model to be far more flexible and efficient. It can be set to control active and reactive powers and voltage magnitude simultaneously. Unlike existing UPFC models, it can be set to control one or more of these parameters in any combination or to control none of them. Limits checking and an effective control co-ordination between controlling devices are incorporated in the enhanced load flow program. The algorithm exhibits quadratic or near-quadratic convergence characteristics, regardless of the size of the network and the number of FACTS devices. - Author(s): J.C.S. Souza ; A.M. Leite da Silva ; A.P. Alves da Silva
- Source: IEE Proceedings - Generation, Transmission and Distribution, Volume 144, Issue 5, p. 445 –455
- DOI: 10.1049/ip-gtd:19971168
- Type: Article
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p.
445
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(11)
Bad data identification is one of the most important and complex problems to be addressed during power system state estimation, particularly when both analogical and topological errors (branch or bus misconfigurations) are to be considered. The paper proposes a new method that is capable of distinguishing between analogical and topological errors, and also of identifying which are the bad measurements or the misconfigurated elements due to unreported or incorrectly reported line outages, bus splits etc. The method explores the discrimination capability of the normalised innovations (the differences between the latest acquired measurements and their corresponding predicted quantities), which are used as input variables to an artificial neural network that provides, in the output, the anomaly identification. Data projection techniques are also used to visualise and confirm the discrimination capability of the normalised innovations. The method is tested using the IEEE 24-bus test system, where several types of errors have been simulated, including single and multiple bad measurements, topology errors involving branches or buses etc. - Author(s): S. Mozaffari ; M. Sameti ; A.C. Soudack
- Source: IEE Proceedings - Generation, Transmission and Distribution, Volume 144, Issue 5, p. 456 –460
- DOI: 10.1049/ip-gtd:19971459
- Type: Article
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p.
456
–460
(5)
The solution of the nonlinear equation for a typical ferroresonant circuit containing a power transformer is shown to be dependent on the value of its initial conditions. It is also shown that a small change in initial conditions leads to a large difference in long-term behaviour of the system, and this makes the future of the system unpredictable. With detailed analysis of many simulation results, the basins of attraction for different chaotic regions of the system are obtained. - Author(s): Y. Shibuya ; S. Fujita ; N. Hosokawa
- Source: IEE Proceedings - Generation, Transmission and Distribution, Volume 144, Issue 5, p. 461 –468
- DOI: 10.1049/ip-gtd:19971134
- Type: Article
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p.
461
–468
(8)
Owing to the operation of the disconnector switch very fast transient overvoltages can generate a voltage oscillation inside the transformer connected to it. A practical method to analyse the oscillation is developed based on the multiconductor transmission-line theory. The analysis is conducted in two steps in the frequency domain: first the whole transformer winding is simulated using a single transmission-line model, and secondly, the phenomena in the first coil are analysed using a multiconductor transmission-line model. The numerical results for an actual 525 kV transformer conform with the experiment. The interturn voltage shows a resonance determined by the travelling waves in the coil. The propagation of travelling waves is visualised using time domain analysis. - Author(s): I.-K. Yu and Y.H. Song
- Source: IEE Proceedings - Generation, Transmission and Distribution, Volume 144, Issue 5, p. 469 –476
- DOI: 10.1049/ip-gtd:19971267
- Type: Article
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p.
469
–476
(8)
A dynamic and linear programming-based approach is investigated for the short-term generation scheduling of thermal units considering the security and environmental constraints of electric power systems. In addition to the basic constraints (i.e. real power limits of the generators, real power demand, spinning reserve, minimum up and down time of units) a comprehensive set of constraints is considered including: transmission line capacity limits, generators dynamic ramp rate, voltage security margin and environmental issues. An optimal multiplier continuation method is adopted to effectively calculate the voltage security margin. The constraint relating to the voltage security margin is considered as a transition constraint in the dynamic programming process. The environmental issue is considered as a restriction on the hourly SO2 emission allowances and other constraints are considered in the dynamic/linear programming procedures. Results of the application of the proposed algorithm to a test system are presented to illustrate the effectiveness of the approach. - Author(s): S.R. Huang
- Source: IEE Proceedings - Generation, Transmission and Distribution, Volume 144, Issue 5, p. 477 –481
- DOI: 10.1049/ip-gtd:19971144
- Type: Article
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p.
477
–481
(5)
The author presents a method of forecasting the hourly load demand on a power system. The forecasting method uses threshold autoregressive models with the stratification rule. With the proposed threshold model algorithm, fewer parameters are required to capture the random component in load dynamics. The techniques employed herein are the determination of an optimum threshold number and the construction of the threshold. The optimum stratification rule attempts not only to remove any judgmental input, but also to render the threshold process entirely mechanistic. Hence, the results demonstrate the proposed method's effectiveness in terms of improving precision and reliability. - Author(s): Md.S. Salam ; K.M. Nor ; A.R. Hamdan
- Source: IEE Proceedings - Generation, Transmission and Distribution, Volume 144, Issue 5, p. 482 –488
- DOI: 10.1049/ip-gtd:19970819
- Type: Article
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p.
482
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(7)
The authors present a comprehensive hydrothermal co-ordination algorithm where a new Lagrangian relaxation based hydrothermal co-ordination algorithm is integrated into an expert system. In this algorithm, the problem is decomposed into the scheduling of individual units by relaxing the demand and reserve requirements using Lagrangian multipliers. Dynamic programming is used for solving the thermal subproblems without discretising generation levels. Instead of solving the hydro subproblems independently as in the standard Lagrangian relaxation approach, hydrothermal scheduling is used to solve the output levels of hydro units. Hydrothermal scheduling uses the commitment status of thermal units obtained from the solutions of the thermal subproblems. The expert system takes care of constraints that are difficult or impractical for implementation in the Lagrangian relaxation based hydrothermal co-ordination algorithm, such as cycling of gas and steam turbine units, etc. It is also applied to check the feasibility of the solution. Extensive constraints such as power balance, spinning reserve, minimum up/down time, must run, capacity limits, ramp rate and hydro constraints are considered. Accurate transmission losses are incorporated. Nonlinear cost function is used, and the hydrothermal scheduling is implemented using a fast and efficient algorithm. Numerical results based on a practical utility data show that this new approach provides feasible schedules within a reasonable time. - Author(s): S.R. Naidu and B.A. de Souza
- Source: IEE Proceedings - Generation, Transmission and Distribution, Volume 144, Issue 5, p. 489 –494
- DOI: 10.1049/ip-gtd:19971432
- Type: Article
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p.
489
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(6)
Determination of the steady-state periodic responses of a ferroresonant circuit is described. The responses were obtained using a time-domain Newton–Raphson procedure and also using a hybrid technique. A continuation procedure is described for determining the multiple solutions of the ferroresonant circuit and the bifurcating solution branches. - Author(s): W.-C. Tsai ; C. Chyn ; T.-P. Tsao
- Source: IEE Proceedings - Generation, Transmission and Distribution, Volume 144, Issue 5, p. 495 –502
- DOI: 10.1049/ip-gtd:19971264
- Type: Article
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p.
495
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(8)
The technical feasibility of using a dynamic flywheel damper to damp shaft torsional oscillations in large turbine generators is investigated. Torsional damping is achieved using the slide friction force of the flywheel damper based on generator speed. A system is defined and the shaft torques following various electrical system disturbances are evaluated and analysed. It is shown that substantial damping can be implemented with a well designed flywheel damper, thus reducing the risk of significant shaft damage due to network disturbances. The equivalent models and designs for the flywheel dampers fitted into the shaft couplings of turbine mechanical systems are also described. This method can effectively damp the torsional oscillations due to the high reliability of the damper. - Author(s): Y.-H. Moon ; E.-H. Lee ; T.-H. Roh
- Source: IEE Proceedings - Generation, Transmission and Distribution, Volume 144, Issue 5, p. 503 –509
- DOI: 10.1049/ip-gtd:19971458
- Type: Article
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p.
503
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(7)
Direct stability analysis using an energy function has recently been widely used for angular and voltage stability analysis in electric power systems. Considerable efforts have concentrated on seeking energy functions for lossy power systems, accomplished only for the simple two-bus system. A new approach is presented to derive an energy function by using the complex integral of bus current equations with respect to bus voltages. Under an assumption that all transmission lines have a uniform R/X ratio, it is shown that the energy function can be developed for multimachine power systems with losses. The proposed energy function is tested on sample systems by comparing the time simulation method, which shows the validity of the proposed method. - Author(s): R.S. Kuruneru and A. Bose
- Source: IEE Proceedings - Generation, Transmission and Distribution, Volume 144, Issue 5, p. 510 –514
- DOI: 10.1049/ip-gtd:19971280
- Type: Article
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p.
510
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(5)
The existing operator training simulators (OTSs) simulate the slow dynamics of power systems in real time but this limits the capability of simulating accurate dynamic behaviour after a disturbance. A feasibility study for the modelling of real time transient stability behaviour in the OTS is described. The goal was to analyse not only the CPU timing for the OTS simulation cycle with real time transient stability analysis but to also investigate the resulting improvements in the quality of the OTS. The results confirm that the transient stability can be simulated in real time for systems of realistic size on readily available workstations. More importantly, the results show significant differences in the dynamic behaviour when transient stability is simulated, strongly suggesting that the present OTSs do not provide enough accuracy for training under certain conditions. - Author(s): M.G. Danikas
- Source: IEE Proceedings - Generation, Transmission and Distribution, Volume 144, Issue 5, page: 515 –515
- DOI: 10.1049/ip-gtd:19971279
- Type: Article
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p.
515
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Computer-based strategy for the restoration problem in electric power distribution systems
Elimination of merchandise surplus due to spot pricing of electricity
Fuzzy logic approach in power system fault section identification
Fuzzy optimisation of capacitors in distribution systems
Short-term power purchases considering uncertain prices
Field studies using a neural-net-based approach for fault diagnosis in distribution networks
Unified power flow controller: a critical comparison of Newton–Raphson UPFC algorithms in power flow studies
Data visualisation and identification of anomalies in power system state estimation using artificial neural networks
Effect of initial conditions on chaotic ferroresonance in power transformers
Analysis of very fast transient overvoltage in transformer winding
Short-term generation scheduling of thermal units with voltage security and environmental constraints
Short-term load forecasting using threshold autoregressive models
Comprehensive algorithm for hydrothermal co-ordination
Newton–Raphson approach for the analysis of ferroresonant circuits
Damping torsional oscillations due to network faults using the dynamic flywheel damper
Development of an energy function reflecting the transfer conductances for direct stability analysis in power systems
Feasibility study of transient stability analysis for operator training simulators
Comment: Online leakage current monitoring of 400 kV insulator strings in polluted areas
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