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Generation, Transmission and Distribution, IEE Proceedings-

Issue 6 • Date Nov 1998

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Displaying Results 1 - 21 of 21
  • Earth-return path impedances of underground cables. I. Numerical integration of infinite integrals

    Page(s): 621 - 626
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (432 KB)  

    Although it is generally acknowledged that there is a need to closely formulate the earth-return path impedances of underground cables, research published so far has mainly concentrated on developing approximate formulations, especially for the infinite integrals which arise. Instead of seeking approximations, the paper develops a rigorous method based on direct numerical integration to evaluate the infinite integrals of underground cable earth-return path impedances. The method has immediate practical use in underground cable parameter calculations. It also provides a benchmark by which the accuracy of any proposed approximate method can be assessed. Further, the method can be used to provide training data by means of which infinite integrals can be evaluated using an array of neural networks View full abstract»

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  • Formula for the effect of a static VAr compensator on synchronising torque coefficient [comment and reply]

    Page(s): 759 - 760
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (140 KB)  

    The author comments on the paper by A.A. El-Emary (see ibid., vol.143, no.6, p.582-6, 1996). The author comments on the correct interpretation of the concept of synchronising torque as raised in a case study of a 9-machine power system discussed in the El-Emary's paper. The original author replies to the comments View full abstract»

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  • Scheduling of radio-controlled heating load

    Page(s): 641 - 646
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (464 KB)  

    An economic loading program has been adapted to enable it to obtain an optimum heat-load profile to meet the forecast heat requirement. The heat load is represented by a `generator' whose load is constrained to be negative. The incremental cost of this unit is a heat energy price. This is adjusted to obtain a heat profile containing the requisite energy. The profile is then used by a dynamic programming algorithm to derive a commitment pattern for each block. A case study is presented which shows that the procedure can minimise heat energy cost. It is also shown that use of the proposed method results in less generator load cycling. This reduced regulation duty should improve reliability View full abstract»

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  • New multi-objective stochastic search technique for economic load dispatch

    Page(s): 747 - 752
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (428 KB)  

    A new multi-objective stochastic search technique (MOSST) for the multi-objective economic dispatch problem in power systems is presented. It is a highly constrained problem with both equality and inequality constraints. The MOSST heuristic has been designed as a combination of real coded genetic algorithms (GA) and simulated annealing (SA). It incorporates a genetic crossover operator BLX-α and a problem specific mutation operator with a local search heuristic to provide a better search capability. Extensive simulations are carried out on standard test systems, considering various aspects, and the results are compared with other methods. These results indicate that the new MOSST heuristic converges rapidly to improved solutions. MOSST is a truly multi-objective technique, as it provides the values of various parameters for optimising different objectives, as well as the best compromise between them, all in a single run. Perturbation analysis shows that the solutions obtained by MOSST are truly pareto-optimal, i.e. no objective can be further improved without degrading the others View full abstract»

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  • Sensitivity analysis for transient stability studies

    Page(s): 669 - 674
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (456 KB)  

    The paper presents a method for security control of electric power systems effected by generation reallocation, determined by sensitivity analysis and optimisation. The model is developed considering the dynamic aspects of the network (transient stability). Security control methodology is developed using sensitivity analysis of the security margin in relation to the mechanical power of synchronous machines in the system. The power reallocated to each machine is determined by means of linear programming. To illustrate the proposed methodology, an example is presented which considers a multimachine system composed of 10 synchronous machines, 45 buses, and 72 transmission lines, based on the configuration of a southern Brazilian system View full abstract»

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  • Tabu search based approach to trouble call analysis [in LV power distribution]

    Page(s): 731 - 738
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (776 KB)  

    A new method for trouble call analysis in low voltage distribution systems based on set covering theory and the tabu search (TS) technique is proposed. First, a new mathematical model for the trouble call analysis is developed based upon customer trouble calls, taking into account the protective device location, selectivity and operation possibility in the distribution network protection schema. Secondly, a new method is presented to solve this problem using a TS-based method to efficiently search for the protective device(s) that was the most likely to have operated. Finally, a sample distribution system is used to demonstrate the feasibility and efficiency of the developed method. Test results suggest that the developed TS-based method is efficient View full abstract»

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  • Practical application of evolutionary computing to reactive power planning

    Page(s): 753 - 758
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (416 KB)  

    The paper presents a practical application of evolutionary programming (EP) to reactive power planning (RPP). The proposed approach has been used in a real power system in England. Simulation results, compared with those obtained by using an improved genetic algorithm (IGA) and a conventional gradient-based optimisation method, Broyden's method, are presented to show that the present method is better for power system planning. Several cases simulating the real network situation of both normal operation and the operation with line outages have been studied. For all these cases, EP is much better than the others. The comprehensive real-state simulation results show a great potential for applications of EP to real-life power system economical and secure operation, planning and reliability assessment View full abstract»

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  • Possibilistic-diagnosis theory for fault-section estimation and state identification of unobserved protective relays using tabu-search method

    Page(s): 722 - 730
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (900 KB)  

    In the paper, an integrated approach is presented for fault-section estimation and state identification of those protective relays whose state information is not available in electrical power dispatching centres using the tabu-search (TS) method. The proposed fault-section estimation method utilises incomplete operational information of protective relays and tripping information of circuit breakers, and is able to deal with the operating reliabilities of protective relays and circuit breakers. At first, based on the logic relationship among section faults, protective relay operation and circuit breaker trip, a 0-1 integer programming model for fault-section estimation and state identification of unobserved protective relays is presented. The developed model is based on recently proposed possibilistic-diagnosis theory under graded uncertainty and the well developed parsimonious set covering theory. In this model, the problem of the fault-section estimation under incomplete information from protective relays is dealt with in a formal and systematic manner, and the operating reliabilities of protective relays and circuit breakers are taken into account at the same time. Secondly, the TS method is used to solve this 0-1 programming model to find the optimal solution efficiently. In addition, an efficient method for identification of faulty subnetworks which include all faulty sections is adopted by using the real-time information from circuit breakers. Extensive test results of a sample power system have demonstrated the correctness of the developed mathematical model and the efficiency of the TS-based method View full abstract»

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  • Technique for contingency monitoring and voltage collapse prediction

    Page(s): 634 - 640
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (672 KB)  

    Investigation and online monitoring of power system stability have become vital factors to electric utility suppliers. At present power system utilities operate very close to the limit of system stability owing to an increasing number of new economic and environmental restrictions. Researchers have been trying to find out the most effective way for online system status monitoring, so that necessary precautions can be taken prior to voltage collapse. Several methods have been proposed for analysing voltage collapse phenomena. An effective method for online system status monitoring and thus voltage collapse prediction is described. The basic methodology implied in this technique is the investigation of each line of the system through calculating line stability indices. The proposed method was tested on the IEEE 24-bus reliability test system and has been found to be accurate and precise in voltage collapse prediction. A comparative study with other methods has also been carried out indicating that the proposed method has some advantages over the others View full abstract»

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  • Improved symmetrical component-based fault distance estimation for digital distance protection

    Page(s): 739 - 746
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (504 KB)  

    An improved symmetrical component-based method is proposed in the paper. The proposed method uses phasor estimates of voltage and current samples obtained from both ends of a power transmission line. The mathematical basis of the new approach is described. It is shown that the new method completely obviates complex arithmetic operations and has considerable computational advantages over the previously proposed methods. Furthermore, performance assessment studies on this new method using the alternative transient program (ATP) are presented and discussed. It is illustrated that the proposed method can determine the fault location very accurately and is likely to be used for digital distance protection and fault location View full abstract»

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  • Measurements of grounding resistances for high impulse currents

    Page(s): 693 - 699
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (508 KB)  

    The paper presents field measurements of surge characteristics of a concrete pole, a buried single conductor and a grounding net for high-impulse currents with a maximum magnitude of 40 kA and with a wavefront duration of a few microseconds. The measured results show that the grounding resistances are greatly dependent on the applied currents and have a hysteresis characteristic. Finally, it is made clear that the grounding resistance has an energy dependence View full abstract»

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  • Protection co-ordination: determination of the break point set

    Page(s): 717 - 721
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (344 KB)  

    Modern power system networks are often multiloop structured. The co-ordinated setting of overcurrent and distance protective relays in such networks is tedious and time consuming. The complicated part of this problem is the determination of a proper minimum set of relays, the so-called minimum break-point set (BPS), to start the co-ordination procedure. The paper presents a new graph-theoretical method to determine a near-to-minimum or a minimum BPS. Using the lemmas of this method, the determination of a minimum BPS can be reduced and decomposed into subproblems. Owing to the efficiency of these lemmas, the presented method quickly achieves the result, even for large networks. Moreover, due to the simplicity of the method, it can be manually applied to the graph of each network. Since the presented lemmas are general, they can be applied to improve any method dealing with BPS determination View full abstract»

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  • Loss and current distribution in foil windings of transformers

    Page(s): 709 - 716
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (548 KB)  

    Detailed loss and current distributions in the foil-wound low-voltage winding of a 6 MVA power transformer using a finite-element analysis package are presented. The foil-winding eddy loss is estimated and its variation with clearance to yoke is examined. Plots of foil current and eddy-current density and loss-intensity distributions are shown and the magnitude and location of their maxima identified. These lead to the main finding that the foil-winding loss distribution is significantly nonuniform not only axially but also radially. This radial variation has been ignored in previous studies. This will have implications for the thermal performance which is outside the scope of the present study. Although the low-voltage foil winding is conventionally the inner winding, it is shown that making it an outside winding can result in a significant reduction in the maximum current density, loss intensity and the winding eddy loss as a percentage of the I2R loss. The radial short-circuit forces on the outside foil winding, being tensile, could also be an advantage. The variation of foil eddy loss with foil thickness is examined View full abstract»

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  • Evaluation of existing optimal VAr planning tools on utility systems

    Page(s): 663 - 668
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (516 KB)  

    Findings of an EPRI project conducting a comprehensive evaluation of optimal VAr planning/OPF tools are reported. Three selected tools were adapted to address VAr allocation studies on four large-scale utility systems. The results obtained indicate that the use of such tools offers significant savings in cost of added MVAr requirements and the number of allocated sites with reasonable and manageable computer execution times. Based on the adaptation requirements for the different programs and studies conducted, recommendations on enhancement areas for the selected tools are provided. One of the major concerns in these studies should be the implementability of the results. This requires careful design including assignment of controls and constraints that can be implemented in the field together with the available tools to provide such requirements View full abstract»

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  • Effect of realistic system modelling on low-voltage capacitor transient overvoltages

    Page(s): 682 - 686
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (332 KB)  

    Although the switching of capacitor banks produces transients, such operations are necessary and an integral part of a power system. The transient produced in this way can propagate through the distribution lines and be magnified in shunt compensated loads. Magnifications of these surges are studied, and it is found that, if there are two LC loops with the same natural frequencies, the transient overvoltage produced by the switching of the capacitor in the first loop is magnified in the second one. The magnification depends on capacitance and frequency ratios. The paper analyses the transient response of a two LC loop system and shows how overhead lines, system interaction, loads and other capacitor banks can affect this magnification. The proposed method is used to analyse the magnification of overvoltages in a real system, and results obtained with and without the consideration of these main item parameters are presented View full abstract»

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  • Analysis of a novel solid state voltage regulator for a self-excited induction generator

    Page(s): 647 - 655
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (732 KB)  

    An analysis of a solid state voltage regulator for a self-excited induction generator (SEIG) using a static condenser (STATCON) is presented. The power circuit of the STATCON-based voltage regulator employs a three-phase current controlled voltage source inverter (CC-VSI) with an electrolytic capacitor in its DC bus. The control scheme consists of two PI voltage controllers and one hysteresis current controller. The mathematical model of the proposed scheme is developed to simulate the improved performance of the SEIG with a STATCON-based voltage regulator. The voltage regulator provides the SEIG with the desirable feature of a synchronous condenser, and is capable of operating in capacitive and inductive modes. The use of STATCON saves the SEIG from de-excitation during the severe condition of load perturbation. It has a fast dynamic response for regulating the voltage when the SEIG faces sudden application/removal of load. The voltage regulating scheme is adaptive to the changing load condition and hence it is possible to operate the SEIG at almost constant voltage from no load to full load View full abstract»

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  • Effect of surface charge on hydrophobicity levels of insulating materials

    Page(s): 675 - 681
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (664 KB)  

    A correlation between the hydrophobic characteristics and accumulation of static charge on several insulating surfaces (ceramic and nonceramic) is studied. This experiment consists of simultaneous measurements of surface charge decay and contact angle recovery against time on samples previously exposed to corona impingement; a comparison between charge decay and hydrophobicity recovery trends is then made. From the data obtained, a lowering of the original hydrophobicity level for each material as a consequence of surface charge accumulation is identified. The decay of surface charge and the corresponding recovery of the initial hydrophobic characteristics with time are observed. Loss and recovery of hydrophobicity resulting from surface charging and charge decay, respectively, are identified as mechanisms occurring not only on polymeric surfaces, but also on ceramic ones. From a number of laboratory studies, it has been confirmed and extensively reported by several researchers that surface charging of insulators due to electrical activity (partial discharging) can be achieved. Based on the above, as well as on the results obtained from this experimental work, surface charging of insulators is a phenomenon which may occur under realistic operational conditions, and is therefore proposed as a factor responsible for the loss of the initial highly hydrophobic characteristics of polymeric insulators and coatings, in addition to other well established mechanisms View full abstract»

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  • High-impedance fault identification using a fuzzy reasoning system

    Page(s): 656 - 661
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (532 KB)  

    A methodology is presented to detect high-impedance faults in radial distribution feeders by means of fuzzy logic reasoning. The proposed technique is based on the analysis of the feeder responses to impulse waves which are periodically injected at the feeder inlet. These responses are compared to standard responses which were previously stored in a database. Standard responses correspond to responses of the feeder operating in normal configurations. A supervisory system processes the information in the database and, using a fuzzy inference machine, indicates possible occurrences of abnormalities. The proposed system has been tested in a real feeder; the relevant results are presented View full abstract»

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  • Earth-return path impedances of underground cables. II. Evaluations using neural networks

    Page(s): 627 - 633
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (604 KB)  

    For pt.II see ibid., vol.145, no.6, p.621-6 (1998). The aim of the paper is to train an array of neural networks to provide a procedure with high accuracy and low computing time requirement for evaluating the earth-return path impedances of underground cables. The training set required is formed by using a direct numerical integration method to evaluate the infinite integrals in the earth-return path formulations. The training is extensive but, once completed, it is valid for any cable configuration as it arises. The training leads to a universal set of weighting coefficients for an array of networks each of which has three input nodes, one output node and two hidden layers. Set up with these coefficients, the computing time requirements in calculating sets of series-path parameters for underground cables is reduced by a factor of about 1000 from that using a direct numerical evaluation of infinite integrals View full abstract»

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  • Development of a SMES system as a fluctuating load compensator

    Page(s): 700 - 708
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (672 KB)  

    The development of a superconducting magnetic energy storage (SMES) device and associated experimental system is described. The IGBT-based power converter bridge is controlled under a pulse width modulation (PWM) scheme, to achieve instantaneous and independent control of active and reactive power flow, to and from the superconducting coil. The SMES device is applied to the problem of fluctuating loads at a distribution level. Two control strategies are described: a direct strategy based on equal and opposite compensation of the active and reactive power components of the fluctuating load; and an optimised strategy where the best use is made of the limited capacity of the SMES device. Both strategies are directed at the minimisation of the voltage fluctuation at the load point. The application of these strategies is demonstrated on the experimental system and their performances compared. The effectiveness of the optimised strategy in reducing the voltage fluctuation when compared with reactive power only compensation is quantified View full abstract»

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  • Practical implementation of a hybrid fuzzy neural network for one-day-ahead load forecasting

    Page(s): 687 - 692
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (524 KB)  

    The paper presents the development and practical implementation of a hybrid short-term electrical load forecasting model for a power system control centre. This hybrid architecture incorporates a Kohonen self-organising feature map with unsupervised learning for classification of daily load patterns, a supervised backpropagation neural network for mapping the temperature/load relationship, and a fuzzy expert system for postprocessing of neural network outputs. This load forecaster requires minimum operator intervention and can be trained adaptively online. The developed model has been tested extensively in the actual operating environment and has been shown to outperform the existing regression-based model View full abstract»

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