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Generation, Transmission and Distribution, IEE Proceedings-

Issue 4 • Date Jul 1998

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Displaying Results 1 - 21 of 21
  • Risk of fatal electric shocks at distribution network MV/LV transformer stations

    Publication Year: 1998 , Page(s): 463 - 467
    Cited by:  Papers (2)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (372 KB)  

    A method is proposed for the analysis of risks of fatal electric shocks associated with (sub)urban distribution MV/LV transformer stations due to earth faults. Models for calculating the probability and frequency of potentially dangerous faults and possible exposures of persons are suggested, the latter based upon data acquired by observation. Expressions for assessing the overall risk for a distribution network are suggested. A practical example is included which discusses some typical cases View full abstract»

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  • Time-domain model for multiconductor power transmission lines

    Publication Year: 1998 , Page(s): 473 - 479
    Cited by:  Papers (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (532 KB)  

    The paper presents a new form of time-domain transmission-line model based on natural modes of oscillation as an alternative to models based on natural modes of wave propagation. The advantage is that a prototype model formed in the frequency domain using the new method can be easily transformed into the time domain for EMTP implementation without the need for numerical convolution of any sort. The proposed transmission-line model is an adaptation of the transformer model proposed by the authors. The structure of the new model, and the analytical procedures required to generate a time-domain version, are clarified in the paper in relation to the modelling of an illustrative 3-phase line View full abstract»

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  • Hydrothermal generation scheduling package: a genetic based approach

    Publication Year: 1998 , Page(s): 451 - 457
    Cited by:  Papers (6)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (648 KB)  

    Novel solution algorithms and results based on a genetic algorithm for solving the hydrothermal generation scheduling (HTGS) problem are presented. This is a nonlinear, combinational optimisation problem which aims to minimise the total fuel costs of a power system while satisfying various local and coupling constraints. This results in a complete and efficient HTGS software package for system operation planning needs. In the thermal unit commitment subproblem, the difficult minimal uptime/downtime constraints are embedded and satisfied throughout the proposed encoding and decoding algorithms. Therefore, the global optimum of the problem can be approached with rather high probability. In the hydroelectric scheduling subproblems, complete solution algorithms and encoding/decoding techniques are proposed for solving different types of hydro plants involving hydraulically independent plants (HIPs), hydraulically coupled plants (HCPs), and pump-storage (P/S) plants. In the proposed approach, the hydraulically coupled plants which are located on the same river are solved concurrently. The difficult water balance constraints caused by hydraulic coupling are embedded and satisfied throughout the proposed encoding and decoding algorithm. The software package is applied with great success to the actual Taipower system, which consists of 34 thermal units, two HIPs, three HCPs, and four P/S units View full abstract»

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  • Future load curve shaping based on similarity using fuzzy logic approach

    Publication Year: 1998 , Page(s): 375 - 380
    Cited by:  Papers (8)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (496 KB)  

    Load forecasting has always been essential to efficient power system planning and operation. In this paper, the authors propose the fuzzy logic approach for next-day load curve shaping based on similarity. The proposed approach has the advantage of dealing not only with the nonlinear part of the forecast load curve but also with load forecasting irrespective of day type. In addition to these advantages, the proposed method is useful in situations where accurate forecasting models are difficult to design. The fuzzy logic approach is used to modify the load curves on similar days to shape the next-day load curve. The suitability of the proposed approach is illustrated through an application to actual load data of the Okinawa Electric Power Company, Japan View full abstract»

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  • Generalised bridge converter model for electromagnetic transient analysis

    Publication Year: 1998 , Page(s): 423 - 429
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (580 KB)  

    A generalised approach to model bridge converters for dynamic simulation is presented in this paper. Any degree of complexity in valve representation in a bridge converter topology can be handled with ease. It is possible to interface this model to a parent (host) electromagnetic transient program, and a method of interfacing to the EMTDC program, in particular, is described. The capability of the model is illustrated through simulation of HVDC converters, where the performance of the proposed model is compared to the EMTDC performance for the HVDC CIGRE Benchmark model View full abstract»

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  • Reduction of harmonic currents generated by discharge lamp systems

    Publication Year: 1998 , Page(s): 363 - 368
    Cited by:  Papers (2)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (496 KB)  

    The paper presents a novel scheme for minimising harmonic currents generated by three-phase systems of discharge lamps. The main idea is to install, in the neutral conductor, a filter with characteristics which allows the first harmonic component to flow with minimum attenuation while higher harmonic components of the neutral current are attenuated. For filter design, a three-phase system of fluorescent lamps is substituted by a Thevenin equivalent seen from the common point of a lamp connection and the ground point of the supply system. It leads to nonlinear Thevenin equivalents when an internal impedance and an equivalent voltage are dependent on the current flowing in the neutral conductor. The equivalent circuits developed are subsequently used for filter design and simulation. Rosenbrock's optimisation procedure is implemented to compute filter parameters. The assumed objective function aims at the impedance for the first harmonic to asymmetrical current flow and large impedance for higher harmonics to reduce harmonic distortion in the supply and neutral currents. The equivalent models developed are applied for simulation of filter working conditions in the neutral conductors. Simulations are verified by laboratory tests, showing good agreement View full abstract»

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  • Online leakage current monitoring of 400 kV insulator strings in polluted areas [reply]

    Publication Year: 1998
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (64 KB)  

    The author replies to comments by Danikas about the paper he co-authored with I. Ramirez-Vazquez and G. Montoya-Tena (see ibid., vol.143, no.6, p.560-4, 1996) regarding the recovery period for RTV-coatings. He points out that the results were obtained on standard- and flat-type porcelain insulators without any RTV-coating, However, several tests have been carried out using the same insulator profiles with RTV-coating. The results obtained were very similar to those for uncoated insulators in a continuous salt fog test (1000 h) following the procedure mentioned in IEC1109 View full abstract»

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  • Multi-area unit commitment for large-scale power systems

    Publication Year: 1998 , Page(s): 415 - 421
    Cited by:  Papers (5)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (664 KB)  

    A large-scale multi-area unit commitment is presented using a Lagrangian relaxation approach. The problem with a transmission network of several thousand buses and lines is equivalently modelled by a system with relatively few areas. Crucial tie-lines between areas are directly modelled. The network within an area is simplified from the application requirements. Based on a DC-flow model, the transmission constraints, as well as system demand and reserve requirements, are relaxed by attaching Lagrange multipliers to form a multiphase optimisation structure. A large-scale problem based on PG&E's power system with more than 2200 buses and 2500 lines is tested. Small cases are also tested for comparison. The numerical testing results show that the method is able to handle transmission constraints in large-scale unit commitment problems View full abstract»

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  • Monitoring and assessment of voltage stability margins using artificial neural networks with a reduced input set

    Publication Year: 1998 , Page(s): 355 - 362
    Cited by:  Papers (4)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (740 KB)  

    A new methodology is proposed for the online monitoring and assessment of voltage stability margins, using artificial neural networks with a reduced input data set from the power system. Within the framework of this methodology, first the system model is reduced using self-organised artificial neural networks and an extended AESOPS algorithm. Then supervised learning of multilayered artificial neural networks is carried out on the basis of this reduced model. Finally, based on the trained network and the reduced set of system variables, monitoring is carried out along with the assessment of voltage stability margins. This methodology is tested comparatively with a methodology for monitoring and assessing voltage stability using a complete input data set. The tests were carried out on a real power system with 92 buses. The results obtained indicate the justifiability of using a reduced system because of the increased efficiency and accuracy of calculation, both in the learning stage and in the recall stage of the artificial neural network View full abstract»

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  • Artificial intelligence in diagnosis and supply restoration for a distribution network

    Publication Year: 1998 , Page(s): 444 - 450
    Cited by:  Papers (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (740 KB)  

    The development of a PC-based integrated system, to illustrate the application of artificial intelligence in the fault diagnosis and supply restoration for an interconnected distribution network is described. The intelligent process utilises the post-fault network status, a list of the tripped breakers, main protection alarm, and the conventional event log. The fault diagnostic system is implemented by three independent mechanisms, namely the generic core rule, specific post-fault network matching, and generic relay inference rules. The intelligent restoration process is implemented by the switching check, the dynamic restoration algorithm and the mechanism for restoration by record matching and learning. By linking to a PC-based distribution simulator it has been demonstrated that the developed mechanisms enable the correct deduction of fault under different network configurations. The appropriate restoration plan can also be generated to restore supply to the entire restorable load for various post-fault networks. This system is currently used for undergraduate teaching and will be ideal for the training of network operation engineers. As the system developed is generic and can be used for a general network, it can be further developed for practical operation in a subtransmission system or an urban distribution system operated in any configuration View full abstract»

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  • Demand-side optimal selection of switching devices in radial distribution system planning

    Publication Year: 1998 , Page(s): 409 - 414
    Cited by:  Papers (5)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (504 KB)  

    Optimal selection of distribution system switching devices is an important consideration in power system planning and operation. The paper formulates the generalised optimisation problem of switching device selection incorporating customer demand-side considerations. This optimisation problem is nonlinear and nondifferentiable with a finite number of solutions. The paper presents a direct search technique and a bisection approach to solve this problem. The two techniques are illustrated and compared using practical distribution systems View full abstract»

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  • Application of genetic algorithms for control design in power systems

    Publication Year: 1998 , Page(s): 345 - 354
    Cited by:  Papers (7)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (932 KB)  

    Proposed is a new method of designing control systems which relies on a combination of advanced system simulators and genetic computation. In contrast with standard approaches applied to control systems, which often rely on a simplified model of a system, this framework provides realistic full-scale modelling abilities, accomplished via system simulators along with the optimisation versatility of genetic algorithms. In particular, genetic algorithms are capable of handling high multivariable and multimodal optimisation problems which usually arise in the setting of complex systems, The method is implemented as an extension to the electromagnetic transients (EMT) program EMTDCTM . The combination of the EMT program and genetic algorithms resulted in a tool for optimal control design in the area of power systems. A method of using this tool and the results of its application to the design of optimal controls for the CIGRE benchmark model and a multi-terminal DC system are presented View full abstract»

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  • Adaptive protection strategies for detecting power system out-of-step conditions using neural networks

    Publication Year: 1998 , Page(s): 387 - 394
    Cited by:  Papers (10)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (756 KB)  

    This paper presents new strategies for adaptive out-of-step (OS) protection of synchronous generators based on neural networks. The neural network architecture adopted, as well as the selection of input features for training the neural networks, are described. A feedforward model of the neural network based on the stochastic backpropagation training algorithm is used to predict the OS condition. Two adaptive OS protection strategies are suggested. The first approach depends firstly on detecting the case of the system through case detection neural networks by some prefault local measurements at the machine to be protected, and then calculating the new OS condition through an adaptive routine. The second approach is based on creating a large neural network to be trained using different outage cases of the power system. The capabilities of the developed adaptive OS prediction algorithms are tested through computer simulation for a typical case study. The results demonstrate the adaptability of the proposed strategies View full abstract»

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  • Electric field analysis for a static induction type of voltage sensor in three-phase power distribution systems

    Publication Year: 1998 , Page(s): 437 - 443
    Cited by:  Papers (3)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (504 KB)  

    The real-time observation of a power factor is going to be indispensable for the maintenance, control and stable voltage regulation of general three-phase power distribution systems in Japan. The voltage in the transmission lines is so high that its waveform must be measured with a static induction type of noncontact voltage sensor, which can be attached simply and at a reasonable price compared with other voltage sensors such as a photovoltage sensor. Since the sensor is constructed from a pair of electrodes, there is likely to be a problem in the discrepancy between the actual voltage waveform and the measured waveform in three-phase power distribution systems. The authors have investigated the cause of the problem in the phase shift between the actual voltage waveform and the measured waveform for the static induction type of voltage sensor. This paper presents the results of the electric field analysis concerning another influence of the overhead ground wire, i.e. that on the phase shift in three-phase power distribution systems View full abstract»

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  • Reconciling pool and contract dispatch in open access transmission operations

    Publication Year: 1998 , Page(s): 468 - 472
    Cited by:  Papers (3)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (508 KB)  

    The dispatch of both suppliers who bid into the pool and of bilateral and multilateral contracts between individual buyers, sellers and brokers are obligations placed on the system operator in an open transmission access environment. During periods of transmission congestion security-driven constraints impose curtailments on all types of transactions. The paper addresses the need to develop methodologies to understand and cope with this problem View full abstract»

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  • Modelling a positive lightning downward leader to study its effects on engineering systems

    Publication Year: 1998 , Page(s): 395 - 402
    Cited by:  Papers (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (728 KB)  

    A mathematical model of a positive lightning downward leader is presented and its radiated EM fields calculated. The approach is based on the idea that a substantial similarity exists between lightning phenomena and the discharge in large airgaps. By assuming the discharge channel to be a long conductor and by using an LCR representation for a single conductor line (L, C and R being, respectively, the inductance, the capacitance and the resistance), a predictive model of the positive lightning can be developed enabling description of the evolution of the whole discharge. Taking into account some atmospheric conditions, the model enables the determination of the leader current and the corresponding charge, its propagation velocities, the potential drop along its channel, the power and energy injected into the gap, the leader and streamer lengths through its propagation and a trajectory of the discharge plotted in 3D in real time obtained from a probabilistic distribution. Furthermore, an application concerning the evolution of the radiated electric and magnetic fields of the leader is given. The results obtained are quite satisfactory View full abstract»

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  • Two aspects of local redundancy in state estimation

    Publication Year: 1998 , Page(s): 458 - 462
    Cited by:  Papers (2)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (372 KB)  

    The two aspects of local redundancy of the measurement in state estimation are presented in the paper. The integer local redundancy ηib for the treatment of bad data and the noninteger local redundancy ηis for smoothing the measurement noise are studied. The differences as well as the relations between these redundancies are also described. These developments are demonstrated in a simple example and the IEEE 30-bus-test-network View full abstract»

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  • Weighted-norm approach for multiobjective VAr planning

    Publication Year: 1998 , Page(s): 369 - 374
    Cited by:  Papers (9)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (536 KB)  

    The paper presents a weighted-norm approach for solving the multiobjective VAr planning problem. First, the weak bus-oriented criterion is used to determine the candidate buses for installing new VAr sources. Next, a weighted-norm (WN) approach based on simulated annealing (SA) is applied to solving general multiobjective VAr planning problems by assuming that the decision-maker (DM) has goals for each of the objective functions. Given the goals specified by the DM, the interactive algorithm can search for a satisfying noninferior solution for the DM. The method presented can obtain a desirable, global noninferior solution and reduce the solution space. Results of application of the proposed method to multiobjective VAr planning are presented View full abstract»

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  • Approach for bus frequency estimating in power system simulations

    Publication Year: 1998 , Page(s): 431 - 435
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (392 KB)  

    Bus frequency affects the system load behaviour in time domain simulation of power systems. The most common methods for estimating bus frequency are by taking weighted averages of the speeds of synchronous machines or by taking time derivatives of the phase angles of bus voltages. These methods cause a simulation accuracy problem or even give wrong results. A new approach for estimating bus frequency is introduced. This takes into account the factors of both machine speeds and phase angles of bus voltages, which is shown to be more accurate in bus frequency estimation and will not increase computer simulation time View full abstract»

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  • Method to improve digital distance relay impedance measurement when used in series compensated lines protected by a metal oxide varistor

    Publication Year: 1998 , Page(s): 403 - 408
    Cited by:  Papers (6)  |  Patents (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (560 KB)  

    A novel method is described that enhances the accuracy of digital distance relays applied on series-compensated lines where the series capacitors are protected against overvoltages by a metal oxide varistor (MOV). The technique is applicable to systems where the relaying voltage is taken from the busbar side of the series capacitor. The basis of the technique is a method known as voltage compensation. The voltage across the series capacitor and overvoltage protective device is calculated in the relay and hence the relaying signal is modified by the relay. The new compensation technique makes the impedance measurement immune to the MOV operation, thus enhancing the relay integrity and the accuracy of impedance measurement. The technique is simulated in a typical differential equation distance relay algorithm and is examined for ground and phase faults using the EMTP (ATP) simulation package View full abstract»

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  • Static VAr compensator (STATCOM) based on single-phase chain circuit converters

    Publication Year: 1998 , Page(s): 381 - 386
    Cited by:  Papers (52)  |  Patents (2)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (768 KB)  

    Voltage-sourced converter circuits using gate turn-off (GTO) thyristors have been proposed as an alternative means of providing static VAr compensation (SVC). Such `advanced SVCs' are classified under the nomenclature STATCOM (STATic COMpensator). The published converter circuits suitable for power system application include the classical Graetz bridge and the multilevel converter. Alternative circuit arrangement has developed with significant advantages in terms of cost and performance; this is in the form of a number of GTO converter links connected in series to form a chain and is referred to as a chain circuit converter. The paper discusses the chain circuit converter and its application to VAr compensation followed by the design and simulated performance of a three-phase STATCOM under both steady state and transient operating conditions. The technical advantages of the chain circuit converter compared with other known arrangements of STATCOM are given. These include good harmonic performance, fast response and improved output at low voltage compared with conventional SVCs. The paper includes comments on the successful testing of two prototype chain links for both leading and lagging reactive currents up to 2000 A peak and concludes with a description of the equipment now being designed for commercial service View full abstract»

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