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IEE Proceedings C (Generation, Transmission and Distribution)

Volume 138, Issue 2, March 1991

Volumes & issues:

Volume 138, Issue 2

March 1991

Effects of abnormal operating conditions on electrical utility planning
  • Author(s): G.I. Dodds  and  W.C. Beattie
  • Source: IEE Proceedings C (Generation, Transmission and Distribution), Volume 138, Issue 2, p. 113 –120
  • DOI:  10.1049/ip-c.1991.0014
  • Type: Article
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  • p. 113 –120 (8)
    Many forecasters have examined normal electricity consumption on long and short time scales, on both a national and an individual basis. This analysis is adequate for normal operating conditions but does not contain any information on the response to an uncertain supply or the effects of energy source depletion. The paper expands the information available by examining the usage of electricity by domestic consumers under uncertain supply conditions. From these usage patterns, disconnection strategies that optimise energy output and service to customers are proposed. The loss of an alternative energy source (town gas) is also examined, and predictions of future demand changes are made.
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Theory of transformer modelling using modal analysis
  • Author(s): D.J. Wilcox
  • Source: IEE Proceedings C (Generation, Transmission and Distribution), Volume 138, Issue 2, p. 121 –128
  • DOI:  10.1049/ip-c.1991.0015
  • Type: Article
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  • p. 121 –128 (8)
    The paper proposes a new structure for transformer models aimed at compact accurate representation of multiwinding transformers under general transient conditions. The paper shows how the fundamental integro-differential equations describing a general transformer may be handled numerically, to give a matrix form corresponding to the Fredholm form of classical transformer analysis. Numerical manipulation of the matrix form, by means of straightforward linear transformations, allows general solution of the transformer equations without the limitations and restrictions of classical analysis. In particular, unlike classical work, the method allows full account to be taken of the frequency-dependent effects and losses arising from transient flux penetration into the transformer core. There is no restriction on the number of windings, and the theory is completely independent of how the windings are eventually connected. The advantage of the method is that a robust solution structure emerges that creates possibilities for very considerable reductions in computational requirements compared with existing alternatives.
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Worst case studies of short-circuit making-currents
  • Author(s): W.F.J. Kersten  and  W.M.C. van den Heuvel
  • Source: IEE Proceedings C (Generation, Transmission and Distribution), Volume 138, Issue 2, p. 129 –134
  • DOI:  10.1049/ip-c.1991.0016
  • Type: Article
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  • p. 129 –134 (6)
    Short-circuit peak currents exceeding the testing value according IEC standards can be caused by the nonsimultaneous closing of the poles of a circuit breaker during switching or reclosing while the network is in short-circuit state and by the successive involvement of the three phases during the development of a three-phase fault as well. The paper treats the theoretical relations of the short-circuit currents during non-simultaneous pole closing or fault development in a network where either the source or the fault is ungrounded. In a network satisfying the IEC test circuit the peak current may reach a value up to 2.1 p.u., this is well above the maximum prospective value of 1.8 p.u. achieved during testing with simultaneous closing of the three phases. The chance of peak currents occurring above 1.8 p.u. have been investigated by TNA (transient network analyser) tests. Parameters are the dispersion in the closing times of the CB poles and the prestrike characteristics of the breaker. The tests indicate that these chances are quite high in modern circuit breakers. The paper also considers the resulting short-circuit current when a short-circuit happens during the energisation of a capacitor bank. In this situation, the chance of peak currents occurring well above 1.8 p.u. is rather small as the required coincidence of conditions is less probable.
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Role and objectives of control for wind turbines
Value of variable sources on power systems
  • Author(s): M.J. Grudd
  • Source: IEE Proceedings C (Generation, Transmission and Distribution), Volume 138, Issue 2, p. 149 –165
  • DOI:  10.1049/ip-c.1991.0018
  • Type: Article
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  • p. 149 –165 (17)
    The paper examines the value of variable power sources, such as wind and tidal energy, on electricity supply systems. A statistical approach is developed for assessing the operational impacts, including thermal plant cycling and operating reserve requirements. It is shown from this analysis that operating penalties are negligible when the capacities involved are small relative to the overall system, as long as reserve is optimally scheduled. Simplified equations are also presented for estimating operating penalties from limited data. The paper then discusses the impact of variable sources at higher system penetrations, and uses modelling studies to examine the possible economic value of wind energy up to very high capacities. The possible technical characteristics of future power systems are discussed in this light. Finally, the paper examines the contribution of variable sources to system reliability and the nature of capital savings arising from this. The capacity contribution in many circumstances is equivalent to conventional sources, but in general the importance of capacity issues is much less than generally believed. The overall conclusion is that for a given energy output, variable sources are often as valuable as equivalent conventional sources when the capacity is small, and their contribution can be very large before the penalties of variability become significant.
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Modified loss coefficients in the determination of optimum generation scheduling
  • Author(s): D. Hazarika  and  P.K. Bordoloi
  • Source: IEE Proceedings C (Generation, Transmission and Distribution), Volume 138, Issue 2, p. 166 –172
  • DOI:  10.1049/ip-c.1991.0019
  • Type: Article
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  • p. 166 –172 (7)
    A modified method has been evolved to form the loss coefficients of an electrical power system network by decoupling load and generation and thereby creating additional ficticious load buses. The system losses are then calculated and co-ordinated to arrive at an optimum scheduling of generation using the standard co-ordination (λ iteration) equation. The method presented is superior to the ones currently available, in that it is applicable to a multimachine system with random variation of load and it accounts for limits in plant generations and line losses. The precise nature of results and the economy in the cost of energy production obtained by this method is quantified and presented.
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