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Online ISSN 1751-8695 Print ISSN 1751-8687

IET Generation, Transmission & Distribution

Volume 3, Issue 4, April 2009

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Volume 3, Issue 4

April 2009

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    • Low-loss HVDC transmission system with self-commutated power converter introducing zero-current soft-switching technique
      • Author(s): T. Senjyu ; K. Kurohane ; J. Miyagi ; N. Urasaki
      • Source: IET Generation, Transmission & Distribution, Volume 3, Issue 4, p. 315 –324
      • DOI:  10.1049/iet-gtd.2008.0078
      • Type: Article
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      • p. 315 –324 (10)
        In recent years, application of self turn-off devices for the HVDC transmission system is very important for flexible and high efficient power transport and supply. However, for self turn-off devices that are applied to high-power system, excessive switching losses due to voltage/current surges occurred on hard switching and the current tail characteristics on turn-off lead to the considerable switching loss. Therefore switching-loss reduction by using a soft-switching technique is very effective for improvement of the considerable switching losses. A self-commutated HVDC circuit topology with soft-switching characteristics is discussed. The proposed topology is able to achieve a zero-current switching in self-commutated power converters. In order to examine the effectiveness of the proposed system, the system is analysed in terms of the characteristics of switching losses through a theoretical approach and computer simulations.
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      Self-adaptive radial basis function neural network for short-term electricity price forecasting
      • Author(s): K. Meng ; Z.Y. Dong ; K.P. Wong
      • Source: IET Generation, Transmission & Distribution, Volume 3, Issue 4, p. 325 –335
      • DOI:  10.1049/iet-gtd.2008.0328
      • Type: Article
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      • p. 325 –335 (11)
        Effective and reliable electricity price forecast is essential for market participants in setting up appropriate risk management plans in an electricity market. A reliable price prediction model based on an advanced self-adaptive radial basis function (RBF) neural network is presented. The proposed RBF neural network model is trained by fuzzy c-means and differential evolution is used to auto-configure the structure of networks and obtain the model parameters. With these techniques, the number of neurons, cluster centres and radii of the hidden layer, and the output weights can be automatically calculated efficiently. Meanwhile, the moving window wavelet de-noising technique is introduced to improve the network performance as well. This learning approach is proven to be effective by applying the RBF neural network in predicting of Mackey–Glass chaos time series and forecasting of the electricity regional reference price from the Queensland electricity market of the Australian National Electricity Market.
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      Binary-arithmetic approach to observability checking in state estimation
      • Author(s): C. Solares ; A.J. Conejo ; E. Castillo ; R.E. Pruneda
      • Source: IET Generation, Transmission & Distribution, Volume 3, Issue 4, p. 336 –345
      • DOI:  10.1049/iet-gtd.2008.0248
      • Type: Article
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      • p. 336 –345 (10)
        An efficient and robust technique for observability checking in power system state estimation based on Gaussian elimination and binary arithmetic is provided. Since the proposed technique uses binary arithmetic, no rounding error, numerical instability or zero identification problems occur. In some cases, the technique may not identify all observable state variables, requiring an additional numerical analysis over a matrix of dimension that is highly reduced. An illustrative example of small size and a realistic case study are used to demonstrate the features of the proposed technique. Adequate conclusions are finally drawn.
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      Learning-based strategy for reducing the multiple estimation problem of fault zone location in radial power systems
      • Author(s): J. Mora-Flórez ; G. Morales-España ; S. Pérez-Londoño
      • Source: IET Generation, Transmission & Distribution, Volume 3, Issue 4, p. 346 –356
      • DOI:  10.1049/iet-gtd.2008.0164
      • Type: Article
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      • p. 346 –356 (11)
        A learning-based strategy that uses support vector machines and k nearest neighbours is proposed for locating the faulted zone in radial power systems, specifically in distribution networks. The main goal is to reduce the multiple estimation of the fault location, inherent in those methods that use single end measurements. A selection of features obtained from the fundamentals of voltages and currents, measured at the power substation, are analysed and used as inputs of the proposed zone locator. Performance of several combinations of these features considering all fault types, different short-circuit levels and variation of the fault resistance, and the system load is evaluated. An application example illustrates the high precision to locate the faulted zone, obtained with the proposed methodology. The proposal provides appropriate information for the prevention and opportune attention of faults, requires minimum investment and overcomes the multiple estimation problem of the classic impedance based methods.
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      Study on AC pollution flashover performance of cap-and-pin and rod insulators at high-altitude sites
      • Author(s): X. Jiang ; J. Hu ; J. Yuan ; Y. Zhang ; F. Mao
      • Source: IET Generation, Transmission & Distribution, Volume 3, Issue 4, p. 357 –364
      • DOI:  10.1049/iet-gtd.2008.0198
      • Type: Article
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      • p. 357 –364 (8)
        The external insulation of electrical equipments is affected by the atmospheric parameters in high-altitude regions. However, there is a lack of studies conducted at the high-altitude sites of 3000 m and above worldwide so far, in contrast to many fruitful ones carried out in the artificial climate chamber. The authors investigate AC pollution flashover performance of cap-and-pin and rod insulators at high-altitude sites with a view to bridging the gap and enriching our understanding in the aspect. The AC artificial pollution tests are conducted at three high-altitude sites of 2820, 3575 and 4484 m, respectively. The results show that the exponents characterising the influence of salt deposit density, non-soluble deposit density and air pressure are 0.297–0.352, 0.122–0.142, 0.535–0.580, respectively; ambient temperature has an obvious effect on the pollution flashover voltages; there is no obvious relation between the insulator profiles and the influence exponents of salt deposit density, non-soluble deposit density, air pressure or ambient temperature.
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      Differential evolution algorithm for static and multistage transmission expansion planning
      • Author(s): T. Sum-Im ; G.A. Taylor ; M.R. Irving ; Y.H. Song
      • Source: IET Generation, Transmission & Distribution, Volume 3, Issue 4, p. 365 –384
      • DOI:  10.1049/iet-gtd.2008.0446
      • Type: Article
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      • p. 365 –384 (20)
        A novel differential evolution algorithm (DEA) is applied directly to the DC power flow-based model in order to efficiently solve the problems of static and multistage transmission expansion planning (TEP). The purpose of TEP is to minimise the transmission investment cost associated with the technical operation and economical constraints. Mathematically, long-term TEP using the DC model is a mixed integer nonlinear programming problem that is difficult to solve for large-scale real-world transmission networks. In addition, the static TEP problem is considered both with and without the resizing of power generation in this research. The efficiency of the proposed method is initially demonstrated via the analysis of low, medium and high complexity transmission network test cases. The analysis is performed within the mathematical programming environment of MATLAB using both DEA and conventional genetic algorithm and a detailed comparative study is presented.
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      Probabilistic technique for sizing FACTS devices for steady-state voltage profile enhancement
      • Author(s): S.O. Faried ; R. Billinton ; S. Aboreshaid
      • Source: IET Generation, Transmission & Distribution, Volume 3, Issue 4, p. 385 –392
      • DOI:  10.1049/iet-gtd.2008.0398
      • Type: Article
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      • p. 385 –392 (8)
        A novel and simple stochastic-based approach to determine the optimal sizing of multiple flexible AC transmission systems (FACTS) devices in a power system for steady-state voltage profile enhancement is presented. In this context, investigations have been conducted on a published test system taking into consideration the uncertainty of the system load and generator scheduling. Two FACTS schemes are considered, namely a Thyristor Controlled Series Capacitor (TCSC) and two static synchronous compensators (STATCOMs) and a unified power flow controller (UPFC) and a STATCOM. The TCSC and UPFC are employed in the system to adjust the natural power sharing of two different parallel transmission lines and therefore enable the maximum transmission capacity to be utilised. Risk indices to estimate the likelihood that the voltage magnitude at a certain bus falls below a desired value is also presented.
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      New spectral decomposition based approach for flicker evaluation of electric arc furnaces
      • Author(s): N. Köse  and  Ö. Salor
      • Source: IET Generation, Transmission & Distribution, Volume 3, Issue 4, p. 393 –411
      • DOI:  10.1049/iet-gtd.2008.0479
      • Type: Article
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      • p. 393 –411 (19)
        A spectral decomposition-based approach is proposed to estimate the light flicker caused by electrical arc furnaces (EAFs) where the system frequency deviates significantly due to the EAF operation. Analytical expressions of the instantaneous light flicker sensation are obtained beginning from a voltage waveform and these expressions are used to obtain a flicker estimation method based on the IEC flickermeter. In the proposed method, the leakage effect of the FFT algorithm due to fundamental frequency variation is reduced by employing a spectral amplitude correction around the fundamental frequency. The eye-brain weighting curve is realised comparing the voltage spectrum with the tabulated normalised IEC flickermeter responses for sinusoidal voltage fluctuations of the IEC standard. The proposed method is tested on both simulated data and field data obtained from three different EAF plants. The comparison with the digital realisation of the IEC flickermeter shows that the method gives satisfactory estimations of both the instantaneous flicker sensation and the short term flicker severity with low computational complexity. The method is especially useful for all other conditions such as disturbances and subsequent system transients where the system frequency deviates without the need for online sampling rate adjustment.
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