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Generation, Transmission and Distribution, IEE Proceedings-

Issue 2 • Date Mar 1997

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Displaying Results 1 - 23 of 23
  • Application of sequential Monte Carlo simulation to evaluation of distributions of composite system indices

    Page(s): 87 - 90
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (380 KB)  

    The reliability of composite power generation and transmission systems with time-varying loads at each bus can be effectively assessed using the sequential Monte Carlo simulation method. This method can also provide information on the distributions of the adequacy indices, which is not possible with other nonsequential approaches. The approach presented uses an annual chronological load curve for each load bus and a sequential Monte Carlo approach for composite power system reliability assessment. The paper presents the basic sequential simulation technique and illustrates its application to obtain distributions of the various composite power system indices for the IEEE reliability test system View full abstract»

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  • Development of constrained-genetic-algorithm load-flow method

    Page(s): 91 - 99
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (844 KB)  

    A genetic-algorithm load-flow algorithm is developed. Methods for satisfying the power balance requirement and the voltage magnitude constraint are then developed and incorporated into the genetic-algorithm method to form a constrained-genetic-algorithm load-flow algorithm for solving the load-flow problem. The robustness of the new load-flow algorithm is enhanced by the dynamic population method, the technique for accelerating the convergence of the optimisation process and the network node sequencing procedure described in the paper. The paper presents study results obtained by applying the new algorithm to study the practical Klos-Kerner 11-busbar system under light-load and heavy-load conditions View full abstract»

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  • Improved simulation of HVDC converter transformers in electromagnetic transient programs

    Page(s): 100 - 106
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (560 KB)  

    In electromagnetic transient simulation, HVDC power converter transformers are normally represented as magnetically independent single-phase units. However, three-limb power converter transformers are often used in HVDC schemes. Single-phase and three-limb three-phase transformer models are derived using a unified magnetic equivalent circuit concept. The new models are verified with laboratory and data. Also, a comparison is made between the transient performance of HVDC power converters with conventional and proposed transformer models View full abstract»

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  • Alternative to Monte Carlo method for the estimation of lightning incidence to overhead lines

    Page(s): 129 - 131
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (256 KB)  

    The electrical shadow method is generally used to calculate the number of direct lightning strokes to an overhead power line. However, the electrogeometric model has been suggested in the past for such computations, applying the Monte Carlo technique. A new analytical method, an alternative to the Monte Carlo technique, using the electrogeometric model is proposed which requires significantly shorter computation time than the Monte Carlo technique. The method is illustrated by a simple example of a single-conductor overhead power line, and compared with the results obtained from the Monte Carlo technique View full abstract»

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  • Mathematical models of a three-level advanced static VAr compensator

    Page(s): 201 - 206
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (436 KB)  

    Two mathematical models of an advanced static VAr compensator (ASVC) are described. One model was obtained using time-domain analysis of the ASVC circuit and then developed into an s-domain model which was used to study the compensator's control system. Both models were validated using a three phase, 4 kVAr hardware model of a three-level ASVC. The time-domain model was also validated using computer simulations carried out with the EMTDC program. Two switching strategies were considered in the study: fundamental frequency modulation (FFM) and selective harmonic modulation (SHEM). The time domain model was used to predict the waveforms at various parts of the ASVC circuit, for both switching strategies View full abstract»

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  • Indices for selecting the best location of PSSs or FACTS-based stabilisers in multimachine power systems: a comparative study

    Page(s): 155 - 159
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (468 KB)  

    One of the first stages in the design of a PSS or a FACTS-based stabiliser in a multimachine power system is the selection of the best installation location. Among the most popular techniques used to perform this selection, two groups of indices from the residue and the damping torque analysis (DTA) methods were considered to be different both in their calculation and principle of derivation. However, the authors have found that these two groups of indices are in fact closely related to each other, and indeed are equivalent under certain conditions. In the paper, this finding is presented by considering the relationship between these two groups of indices and shows how equivalence may be concluded. Thus a deeper insight into the residue and DTA methods emerges which facilitates a comparison between the accuracy of these indices View full abstract»

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  • Application of optimum stratified sampling and separate ratio estimation in stochastic copper loss of transmission system evaluation

    Page(s): 207 - 212
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (556 KB)  

    A combined Monte Carlo and optimum stratified sampling method is presented to better estimate copper loss of a transmission system during a prespecified future period. This design seeks to enhance the precision of copper loss of transmission system estimation, while reducing computation time. The techniques included are optimum stratified sampling and separate ratio estimation. The optimum stratification rule aims to remove any judgmental input and to render the stratification process entirely mechanistic. The estimator, provided by ratio statistics of the sample, can avoid identification of the regression model and thus save computation time. The effectiveness of precision improvement is demonstrated View full abstract»

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  • Large-scale economic dispatch using an improved Hopfield neural network

    Page(s): 181 - 185
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (500 KB)  

    The application of Hopfield neural networks to the solution of large-scale economic-dispatch (ED) problems is proposed. A special methodology for improving the performance of Hopfield neural networks for solving combinatorial-optimisation problems has already been published. That method is quicker and more accurate. Accordingly, Gee's Hopfield neural networks (GHN) have been used instead of standard Hopfield neural networks. Gee's method has been modified to solve ED. Constraints are handled using a combination of Gee's model and Abe's model. An efficient simulation algorithm is discussed for solving the economic-dispatch problem. The proposed method (PHN) has achieved efficient and accurate solutions for power systems with 3, 20, 40, 80, 120, 160 and 240 units. The PHN results are very close to those obtained using classical numerical methods View full abstract»

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  • Artificial intelligence algorithms for short term scheduling of thermal generators and pumped-storage

    Page(s): 193 - 200
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (764 KB)  

    The authors develop two algorithms for scheduling pumped-storage and thermal generators in a 24 hour schedule horizon based on the heuristic-guided depth-first search method. They differ primarily in the scheduling strategy for guiding the search process in determining the optimal schedule efficiently. In the first algorithm, the idea of the scheduling strategy is to schedule pumped-storage generations at peak load periods in such a way that the remaining load demand curve for thermal generation scheduling has a flattened peak region. In the second algorithm, the scheduling strategy allows pumped-storage generations to be scheduled at peak loads only when commitment of a thermal unit is required to meet the load demand. The operational constraints of the thermal and pumped-storage units together with the volume constraints of the reservoirs are fully taken into account in the algorithms. The effectiveness of the developed algorithms are demonstrated by applying them to a real life power system of 29 thermal units and two pump units View full abstract»

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  • Decomposition approach to unit commitment with reactive constraints

    Page(s): 113 - 117
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (416 KB)  

    The authors propose an efficient algorithm for considering reactive power and voltage constraints in unit commitment. The inclusion of these reactive constraints in unit commitment will ensure enough commitment of real power and a feasible distribution of reactive power in power systems. Because the problem is a large mixed-integer programming and has a two-level hierarchical structure, the Benders decomposition method is used. Using decomposition, the master problem solves unit commitment and the subproblem examines reactive power and voltage constraints every hour to test the feasibility of the unit commitment solution. In the case of infeasibility, a proper constraint (Benders cut) is introduced and placed in the master problem for rescheduling the units. The iterative process provides a minimum cost solution for generation scheduling while satisfying reactive constraints. Test examples on the modified IEEE 30 bus system are presented to demonstrate the efficiency of the method View full abstract»

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  • Digital algorithms for measurement of voltage flicker

    Page(s): 175 - 180
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (584 KB)  

    The fluctuation of utility voltage often becomes so serious that the flicker of electrical lighting equipment is visible and sometimes irritable. In order to solve the problems related to voltage fluctuation, many definitions and meters had been proposed and developed. In this paper, these meter principles are categorised, and the digital algorithms used to calculate voltage flicker are discussed. Special attention is focused on the pitfalls of the fast Fourier transform, which is the spectrum of voltage fluctuation signals. Since the trivial system frequency deviation may cause serious leakage under proper frequency resolution, the directly digital demodulation method is not suggested. In order to reduce aliasing, a low-pass filter (LPF) is necessary, and the sampling frequency of the analog to digital converter (ADC) must be not less than two multiples of the cut-off frequency of the LPF. The frequency resolution must be raised as much as possible to lower the inherent picket-fence effect, owing to the approximately continuous spectrum distribution of the voltage fluctuation. Based on the above considerations, a developed microcomputer-based instrument system prototype was used to validate the operation of the proposed algorithm, by the voltage-flicker measurement of a voltage-flicker generator and an arc-furnace feeder View full abstract»

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  • Fuzzy rule-based expert system for power system fault diagnosis

    Page(s): 186 - 192
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (672 KB)  

    The paper demonstrates a novel component oriented fuzzy expert system (COFES) developed in PROLOG for power system fault diagnosis. This `expert system' assesses faults on power systems using intelligent techniques that can take account of bad/missed SCADA data. Incorrect operation of protective relays and/or circuit breakers during single as well as multiple faults and corresponding uncertain incoming information render proper fault diagnosis a very involved task. To handle these uncertainties and rank various fault hypotheses a fuzzy signal model based on fuzzy information theory has been developed. The model measures degree of correctness of received and nonreceived input data. The proposed method incorporates fuzzy symbol classification through an enhanced knowledge-base which includes network model, predefined subnetworks, relaying schemes and fuzzy diagnostic rules. This expert system has been applied to a sample power system. The results obtained along with their evaluations are completely reported View full abstract»

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  • Improvement of network damping and transient stability by active and reactive power control

    Page(s): 125 - 128
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (388 KB)  

    It is shown how FACTS can be used to improve the dynamic behaviour of electrical power systems. The aspects presented for the applications of compensators are damping of power oscillations and amelioration of transient stability. Control strategies based on local measurable quantities are derived using the direct Lyapunov method, and the relation between observability, controllability and effectiveness of active and reactive power control is discussed View full abstract»

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  • Exact analysis of a multipulse shunt converter compensator or Statcon. I. Performance

    Page(s): 213 - 218
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (604 KB)  

    As the converter we take a voltage sourced inverter bridge with perfect switches. There is a single capacitor on the DC side and the output is connected to an AC system through an inductive link. By changing the phase, θo, of the operation of the inverter switches relative to phase of the AC system, the voltage across the capacitor can be controlled thus controlling the magnitude of the fundamental of the inverter AC output voltage. The difference between the inverter output voltage and the AC system voltage determines the flow of reactive power through the linking inductor to or from the system. Analysis shows that the reactive power is approximately given by the simple relationship Q≈-V2/X[q1+q2θob] where X is the reactance of the inductive link, R is the combined resistance of the link and bridge and θob=2Xθ o/R is a control parameter. The coefficients q1 and q2 are functions mainly of √(XY) where Y is the susceptance of the capacitor at supply frequency and of the number of pulses in the inverter; q1 is small and q2≃0.5 for a well-designed equipment. There is a size of the passive elements below which the performance of the compensator is poor and above which it is not greatly enhanced. The required passive components are smaller than are needed for a compensator formed from switched capacitors and thyristor controlled inductors. Increasing the number pulses in the inverter by using phase shifting transformers, reduces the size of the passive components that are required as well as reducing the magnitude of the harmonic currents in the output View full abstract»

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  • Urban underground network expansion planning

    Page(s): 118 - 124
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (744 KB)  

    The authors describe a three step approach to the expansion planning of high voltage (HV) urban underground distribution networks. Although the techniques are specifically oriented to underground systems, they are equally applicable to overhead power system design. The fundamental engineering problem is how to connect individual high voltage to low voltage substations (HV/LV SS) and zone HV SS into a future urban underground network. The problem is to rearrange the HV network to minimise the cost of expansion subject to provision of an alternative supply, specified load transfer among the neighbouring zone SS, and other general planning constraints such as feeder capacity, voltage regulation, operational requirements and losses. A review of the current state of the art of distribution expansion planning is provided. The normal manual approach is discussed together with more recent research into computer methods. Three lines of computer research are identified and classified as radially constrained, security constrained and utilisation of travelling salesman/vehicle routing problem algorithms (TSP/VRP). The TSP/VRP line of research has been extended here to produce practical techniques for the assistance of network planners View full abstract»

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  • Improved techniques for hybrid method in fast-transient stability assessment

    Page(s): 107 - 112
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (560 KB)  

    The theoretical background and the development of new techniques for the implementation of hybrid methods in online fast-transient stability assessment are presented. For evaluation of transient energy margin (TEM) along a trajectory, a transformed transient energy function (TEF) is defined. It is proved that along a postfault trajectory the transformed TEF is conserved. Based on the conservation principle and using techniques such as integration stopping criteria and location of the main potential energy peak, an improved pseudofault method for TEM evaluation is reported. These techniques have been tested on several test power systems with different system models. Results show that the proposed techniques are useful. An example shows the improvement of the techniques over the recently published hybrid method View full abstract»

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  • Hybrid approach using counterpropagation neural network for power-system network reduction

    Page(s): 169 - 174
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (688 KB)  

    A hybrid counterpropagation neural network and Ward-type equivalent approach for power system network reduction is proposed for improving the conventional external system equivalent technique. The proposed Ward-type equivalent technique not only possesses the good properties of the extended Ward equivalent, but can also update the parameters of the equivalent model for representing real-time topology changes of the external system. Another improvement is that a counterpropagation neural network is used to match the boundary equivalent power injections. The new hybrid approach combines the simplicity of Ward-type equivalent techniques with the speed of artificial neural networks. Test results demonstrate that the hybrid approach is very efficient and highly accurate compared to the external system equivalent View full abstract»

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  • Efficient loss-of-load cost evaluation by combined pseudo-sequential and state transition simulation

    Page(s): 147 - 154
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (940 KB)  

    A new methodology to evaluate loss of load cost (LOLC) indices in composite generation and transmission systems is presented. The proposed approach is based on a combination of pseudo-sequential, state transition and conditional Monte Carlo simulation techniques. The approach can be easily implemented and it only requires models with stationary Markov transitions. Case studies with the IEEE Modified Reliability Test System and the Brazilian Southeastern System are presented and discussed View full abstract»

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  • Probabilistic approach for fault-section estimation in power systems based on a refined genetic algorithm

    Page(s): 160 - 168
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1084 KB)  

    A systematic and mathematically sound model and a refined genetic algorithm (RGA) based method for fault-section estimation in power systems is proposed. First, the probabilistic causality relationship among section fault, protective relay action and circuit breaker trip is formulated as a probabilistic causality matrix. Secondly, the well-developed parsimonious set covering theory is applied to the fault-section estimation problem, and a 0-1 integer programming model is then obtained. Thirdly, a RGA-based method for fault-section estimation is developed by using information on operations of protective relays and circuit breakers. The proposed method is versatile and can deal with uncertainties in fault-section estimation, such as protective relay failures and/or malfunction and circuit breaker failures and/or malfunction. Test results for a sample power system have shown that the probabilistic approach developed for fault-section estimation is feasible and efficient View full abstract»

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  • Linear indicator for voltage collapse in power systems

    Page(s): 139 - 146
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (760 KB)  

    A new linear indicator is presented together with a comparative study with other published works. The salient advantage of the linear characteristic is emphasised. The new index is tested utilising the IEEE 30 bus test power system View full abstract»

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  • On-line dynamic-security contingency screening and ranking

    Page(s): 132 - 138
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (752 KB)  

    An on-line dynamic-security contingency screening and ranking system for large complex power systems, online algorithms for system-instability studies (OASIS), developed which is intended to provide a list of ranked contingencies for the current operational state of the power system every 15 min. A high-speed power-system simulator is used to predict, in real time, transient and dynamic stability from any initial power-system state together with an appropriate contingency list. OASIS uses a client/server model and is designed to run on a heterogeneous computer network to avoid any limit to system size. The prototype of the assessor was completed in mid 1994 and field trials were carried out within an operational power-system-control centre using real online data taken from the system energy-management system. Implementation of OASIS and the results of the field trials are described View full abstract»

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  • Evaluation of load shedding to prevent dynamic voltage instability based on extended fuzzy reasoning

    Page(s): 81 - 86
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (484 KB)  

    A reliable load-shedding approach, which makes use of a knowledge base and extended fuzzy reasoning, is proposed to arrest dynamic voltage insecurity following a disturbance. Irrespective of the nature of the dynamic voltage instability, the location and required amount of load shedding among load control buses can be promptly presented in real-time to the system operators. In the development of this scheme, load control buses are then correlated with the real load-shedding amounts decided during the offline simulation study. The load-shedding amount for previously unseen operating cases at each load control bus can be conservatively predicted according to the zone within which the fuzzy indicator falls View full abstract»

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  • Exact analysis of a multipulse shunt convertor compensator or Statcon. II. Analysis

    Page(s): 219 - 224
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (456 KB)  

    For pt.I see ibid., vol.144, no.2, 213-18 (1997). The derivation of the equations whose characteristics were discussed in part I links together linear circuit behaviour between switching epochs of the inverter. Fourier components of the composite current waveforms are found giving the reactive and active power transferred together with harmonics. The analysis is essentially algebraic View full abstract»

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