Online ISSN
1751-8695
Print ISSN
1751-8687
IET Generation, Transmission & Distribution
Volume 2, Issue 3, May 2008
Volumes & issues:
Volume 2, Issue 3
May 2008
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- Author(s): S.-Y. Ruan ; G.-J. Li ; B.-T. Ooi ; Y.-Z. Sun
- Source: IET Generation, Transmission & Distribution, Volume 2, Issue 3, p. 311 –320
- DOI: 10.1049/iet-gtd:20070021
- Type: Article
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p.
311
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(10)
As gas turbines, wind farms, run-of-river hydro, photovoltaic and other renewable energy sources are becoming a growing component in the power system, the feasibility of applying the controllability of their expensive frequency-changers [based on voltage-source converters or (VSCs)] is examined to provide system damping. It is shown that irrespective of the location of the VSC-frequency changers along the transmission line, significant damping is available by the combined control of real and reactive power modulations. The finding is reached by eigenvalue analysis of the linearised equations and confirmed by digital simulation (PSCAD/EMTDC). Digital simulation is also applied to evaluate the size of injected complex power required for the best damping for a given converter rating. - Author(s): K. Kivikko ; A. Mäkinen ; P. Järventausta ; A. Silvast ; P. Heine ; M. Lehtonen
- Source: IET Generation, Transmission & Distribution, Volume 2, Issue 3, p. 321 –329
- DOI: 10.1049/iet-gtd:20060532
- Type: Article
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p.
321
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(9)
Electricity supply reliability and interruption costs are nowadays of great interest. Large blackouts around the world have aroused also customers' interest in the reliability of distribution networks. In addition to this, reliability worth values are widely used in the regulation of distribution companies, and they can offer an excellent tool for focusing the network investments on the most critical areas in the network. In Finland, Helsinki University of Technology and Tampere University of Technology as well as several Finnish distribution network companies worked on a common project concerning the updating of reliability worth values in 2004-2005. This paper presents the analysis methods used in that study, the elimination techniques to remove the strategic or deviating responses from the survey data and correlation studies to depict how the harm depends on the size of the respondent. - Author(s): J.-H. Teng
- Source: IET Generation, Transmission & Distribution, Volume 2, Issue 3, p. 330 –340
- DOI: 10.1049/iet-gtd:20070165
- Type: Article
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p.
330
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(11)
The mathematical models of distributed generations (DGs) are integrated into three-phase distribution load flow program to analyse and simulate the penetrations of DGs for distribution systems. DGs can utilise the traditional energy sources such as oil and coal or renewable energy sources such as wind, solar and fuel cell and use rotating generators or converters to transfer energy to power grids. According to the characteristics of output power, DGs can be specified as constant power factor model, constant voltage model or variable reactive power model in the load flow analysis. These three models are all derived and integrated into the proposed load flow method. Test results demonstrate the validity and capability of the proposed method. - Author(s): S.-H. Li and H.-D. Chiang
- Source: IET Generation, Transmission & Distribution, Volume 2, Issue 3, p. 341 –354
- DOI: 10.1049/iet-gtd:20070192
- Type: Article
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p.
341
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(14)
Continuation power flow is a powerful tool to simulate power system steady-state stationary behaviours with respect to a given power injection variation scenario. Although continuation power flow methods have been implemented in several commercial packages, they may be still too slow for online applications. The authors aim to improve the continuation power flow methods, mainly their speed and, to a less extent, their reliability. Nonlinear predictors are developed based on the polynomial interpolations. The authors' numerical studies show that continuation power flow with the proposed nonlinear predictors can be much faster than that with traditional linear predictors such as tangent or secant predictors. Of the nonlinear predictors, second-order polynomial approximation-based and third-order-based nonlinear predictors show their superior performance in speed. Continuation power flow with second-order nonlinear predictors is generally slightly faster than that with third-order nonlinear predictors. In addition, a hybrid corrector is developed and incorporated into continuation power flow. It is numerically shown on several test systems ranging from 118-bus to 1648-bus that continuation power flow with the proposed hybrid corrector can be much faster than that with traditional correctors such as the Newton method and the fast decoupled method. Finally, an improved continuation power flow with the developed nonlinear predictor and hybrid corrector is presented and evaluated. - Author(s): T.T. Nguyen and R. Gianto
- Source: IET Generation, Transmission & Distribution, Volume 2, Issue 3, p. 355 –372
- DOI: 10.1049/iet-gtd:20070125
- Type: Article
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p.
355
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(18)
The paper develops a new design procedure for online control coordination which leads to adaptive power system stabilisers (PSSs) and/or supplementary damping controllers of flexible ac transmission system (FACTS) devices for enhancing the stability of the electromechanical modes in a multimachine power system. The controller parameters are adaptive to the changes in system operating condition and/or configuration. Central to the design is the use of a neural network synthesised to give in its output layer the optimal controller parameters adaptive to system operating condition and configuration. A novel feature of the neural-adaptive controller is that of representing the system configuration by a reduced nodal impedance matrix which is input to the neural network. Only power network nodes with direct connections to generators and FACTS devices are retained in the reduced nodal impedance matrix. The system operating condition is represented in terms of the measured generator power loadings, which are also input to the neural network. For a representative power system, the neural network is trained and tested for a wide range of credible operating conditions and contingencies. Both eigenvalue calculations and time–domain simulations are used in the testing and verification of the dynamic performance of the neural-adaptive controller. - Author(s): E. Carpaneto and G. Chicco
- Source: IET Generation, Transmission & Distribution, Volume 2, Issue 3, p. 373 –382
- DOI: 10.1049/iet-gtd:20070280
- Type: Article
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p.
373
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(10)
The electrical load pattern representing the residential consumption is subject to different types of uncertainty, depending on family composition, lifestyle, number and type of use of the electrical appliances, thus requiring a dedicated analysis within a probabilistic framework. A comprehensive approach to the probabilistic characterisation of aggregated residential consumers supplied by the same feeder or substation, from the point of view of the electricity supplier, is presented. Starting from the result of a statistical study carried out on single-house extra-urban residential consumers, the time evolution of the average value and the standard deviation of the aggregated load power are presented. In addition, a dedicated goodness-of-fit analysis has been carried out to identify the most suitable probability distributions representing the daily aggregated load pattern at different times, referred to a set of typical days. This analysis includes a novel characterisation of the critical error of the Kolmogorov–Smirnov test on various probability distributions (beta, gamma, Gumbel, log-normal, Rayleigh and Weibull) for which the critical errors are not specifically available in publications. The gamma and log-normal probability distributions have emerged as the most promising solutions for several time intervals of analysis and for different numbers of aggregated consumers. - Author(s): M.-Y. Huang ; C.-S. Chen ; C.-H. Lin ; M.-S. Kang ; H.-J. Chuang ; C.-W. Huang
- Source: IET Generation, Transmission & Distribution, Volume 2, Issue 3, p. 383 –392
- DOI: 10.1049/iet-gtd:20070206
- Type: Article
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p.
383
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The immune algorithm (IA) is proposed to derive the rephasing strategy arrangement of laterals and distribution transformers to enhance three-phase balancing of distribution systems. The multi-objective function is formulated by considering the unbalance of phasing currents, the customer service interruption cost (CIC) and labour cost to perform the optimal rephasing strategy. For each feasible rephasing strategy, the number of customers affected with total interruption load demand and outage duration time are used to calculate the impact of system reliability because of rephasing engineering works. To demonstrate the effectiveness of the proposed methodology, a practical distribution feeder in Taipower with 271 customers is selected for computer simulation. By minimising the objective function subjected to the operation constraints, the rephasing strategy has been derived by selecting the laterals and distribution transformers for phasing adjustment. It is found that the neutral current of test feeder has been reduced to be less than the neutral overcurrent limit by executing the rephasing of laterals and distribution transformers. - Author(s): D.J. Swaffield ; P.L. Lewin ; S.J. Sutton
- Source: IET Generation, Transmission & Distribution, Volume 2, Issue 3, p. 393 –401
- DOI: 10.1049/iet-gtd:20070142
- Type: Article
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p.
393
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To manage a cable network effectively it is desirable to rate cable assets precisely. To investigate the conservatism of cable ratings provided by accepted modelling approaches several models have been employed to provide comparative continuous ratings for a directly buried cable group arrangement. Operational ratings are performed using expedient cable rating calculations, typically employing analytical or one dimensional (1D) finite difference (FD) methods. The case for a directly buried cable group is considered; ratings are obtained using three methods including the international standard analytical approach (IEC 60287), 1D FD and a 2D finite element analysis (FEA) approach. A continuous equation for resultant heat-flux has been derived to more precisely model the dielectric loss in 2D and 3D FEA models. Comparing results shows that all the models have good agreement when modelling an isothermal ground surface condition and validate the 2D FEA model against established approaches. The FEA model developed has been used to investigate more realistic ground surface boundary conditions. Results for different cable burial depths and ground surface boundary conditions show that using the established methods can lead to overestimation of cable ratings in the case of shallow buried cables. - Author(s): M.W. Mustafa ; S.N. Khalid ; H. Shareef ; A. Khairuddin
- Source: IET Generation, Transmission & Distribution, Volume 2, Issue 3, p. 402 –413
- DOI: 10.1049/iet-gtd:20070354
- Type: Article
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p.
402
–413
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A novel method to identify the reactive power transfer between generators and load using modified nodal equations is proposed. On the basis of the solved load flow results, the method partitions the Y-bus matrix to decompose the current of the load buses as a function of the generators' current and voltage. Then it uses the load voltages from the load flow results and decomposed load currents to determine reactive power contribution from each generator to loads. The validation of the proposed methodology is demonstrated by using a simple 3-bus system and the 25-bus equivalent system of south Malaysia. Next part here focuses on creating an appropriate artificial neural network (ANN) to solve the same problem in a simpler and faster manner. The basic idea is to use supervised learning paradigm to train the ANN. Most commonly used feedforward architecture has been chosen for the proposed ANN reactive power transfer allocation technique. Almost all system variables obtained from load flow solutions are utilised as an input to the neural network. Moreover, tan-sigmoid activation functions are incorporated in the hidden layer to realise the nonlinear nature of the reactive power transfer allocation. The targets of the ANN corresponding to the previously developed reactive power transfer allocation method. The 25-bus equivalent system of south Malaysia is utilised as a test system to illustrate the effectiveness of the ANN output compared with that of the modified nodal equations method. The ANN output provides promising results in terms of accuracy and computation time. - Author(s): M. Basu ; S.P. Das ; G.K. Dubey
- Source: IET Generation, Transmission & Distribution, Volume 2, Issue 3, p. 414 –423
- DOI: 10.1049/iet-gtd:20060317
- Type: Article
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p.
414
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The unified power quality conditioner (UPQC) is one of the major custom power solutions, which is capable of mitigating the effect of supply voltage sag at the load end or at the point of common coupling (PCC) in a distributed network. It also prevents the propagation of the load current harmonics to the utility and improves the input power factor of the load. The control of series compensator (SERC) of the UPQC is such that it injects voltage in quadrature advance to the supply current. Thus, the SERC consumes no active power at steady state. The other advantage of the proposed control scheme is that the SERC can share the lagging VAR demand of the load with the shunt compensator (SHUC) and can ease its loading. The UPQC employing this type of quadrature voltage injection in series is termed as UPQC-Q. The VA requirement issues of SERC and SHUCs of a UPQC-Q are discussed. A PC-based new hybrid control has been proposed and the performance of the UPQC-Q is verified in a laboratory prototype. The phasor diagram, control block diagram, simulations and experimental results are presented to confirm the validity of the theory. - Author(s): D.Z. Fang ; L. Jing ; T.S. Chung
- Source: IET Generation, Transmission & Distribution, Volume 2, Issue 3, p. 424 –432
- DOI: 10.1049/iet-gtd:20070218
- Type: Article
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p.
424
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A new model describing the uncertainty of fault clearing time for probabilistic transient stability assessment of power systems is proposed. In this, a corrected transient energy function-based strategy is developed to evaluate the probabilistic instability index of systems. The advantage of this approach is that evaluations of critical clearing time in the system stability probability assessment are only conducted for very severe contingencies, an extremely small fraction of all considered contingencies. Hence, the computation efficiency has been remarkably enhanced. Case studies on a representation of the North China power system are reported to show that the proposed assessment strategy is effective and practical. - Author(s): B. Grčar ; J. Ritonja ; B. Polajžer ; A.M. Stanković
- Source: IET Generation, Transmission & Distribution, Volume 2, Issue 3, p. 433 –443
- DOI: 10.1049/iet-gtd:20070414
- Type: Article
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p.
433
–443
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Several new methods for faulted transmission line parameters estimation in phasor and time domain are proposed, that eventually improve the overall performance of numerical distance relays. The concept of dynamic phasors is introduced to accommodate the time-variant nature of the current and voltage signals during transients and faults. Based on dynamic phasor transmission line models, direct and indirect estimation methods are derived. For the proposed indirect estimation method, stability of prediction error dynamics is assured by using the Lyapunov direct method. Presented estimation techniques are compared with a conventional stationary phasor solution as well as with a recursive least-square estimator derived in the discrete time domain. In the evaluation, more realistic assumptions are considered with regards to distortion of the input voltage and current signals along with the variable fault resistance because of arcing faults. Simulation results and actual field measurements are included for performance evaluation of the proposed estimators. - Author(s): E.G. Carrano ; R.T.N. Cardoso ; R.H.C. Takahashi ; C.M. Fonseca ; O.M. Neto
- Source: IET Generation, Transmission & Distribution, Volume 2, Issue 3, p. 444 –455
- DOI: 10.1049/iet-gtd:20070174
- Type: Article
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444
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A genetic algorithm that is dedicated to the expansion planning of electric distribution systems is presented, with incremental expansion scheduling along a time horizon of several years and treated as a dynamic programming problem. Such a genetic algorithm (called dynamic programming genetic algorithm) is endowed with problem-specific crossover and mutation operators, dealing with the problem through a heuristic search in the space of dynamic programming variables. Numerical tests have shown that the proposed algorithm has found good solutions that considerably enhance the solutions found by non-dynamic programming methods. The algorithm has also shown to work for problem sizes that would be computationally infeasible for exact dynamic programming techniques. - Author(s): J. Quispe Puma and D. Graciela Colomé
- Source: IET Generation, Transmission & Distribution, Volume 2, Issue 3, p. 456 –467
- DOI: 10.1049/iet-gtd:20070170
- Type: Article
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p.
456
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A methodology is presented to identify parameters of non-linear models of excitation systems (ESs). Based on the use of genetic algorithms (GAs), the proposed methodology carries out simultaneous parameter identification of linear and non-linear model components. The computational algorithm allows to adequately identify model parameters and it is not affected by the noise present in the measurements. The application of this methodology was developed to identify and validate ES models of different technologies that are used in stability studies through dynamic simulations. First, model parameters of DC1A and ST1A type ES were determined in a simulation environment. The performance of two identifiers based on a GA paradigm is analysed: GA with arithmetic and intermediate recombination operators (GA-BASE) and GA based on differential evolution (GA-DE) mutation. Then the GA-DE identifier is applied to estimate parameters of a static ES (EXE) model of a Brazilian hydro power plant utilising measurements corrupted by noise and registered during field tests. The results obtained are satisfactory and the responses of the identified models are close to real system measurements.
Power system damping from real and reactive power modulations of voltage-source-converter station
Comparison of reliability worth analysis methods: data analysis and elimination methods
Modelling distributed generations in three-phase distribution load flow
Nonlinear predictors and hybrid corrector for fast continuation power flow
Neural networks for adaptive control coordination of PSSs and FACTS devices in multimachine power system
Probabilistic characterisation of the aggregated residential load patterns
Three-phase balancing of distribution feeders using immune algorithm
Methods for rating directly buried high voltage cable circuits
Reactive power transfer allocation method with the application of artificial neural network
Investigation on the performance of UPQC-Q for voltage sag mitigation and power quality improvement at a critical load point
Corrected transient energy function-based strategy for stability probability assessment of power systems
Estimation methods using dynamic phasors for numerical distance protection
Power distribution network expansion scheduling using dynamic programming genetic algorithm
Parameters identification of excitation system models using genetic algorithms
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