Environmental Engineering Reference
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but is very much more computationally demanding. Transient simulation is used to model
lighting and other fault conditions requiring very detailed analysis of systems with relatively
few nodes.
Many power system simulation packages now include facilities to model renewable energy
generators such as wind turbines and wind farms. A few years ago, the models tended to be
little more than a 'negative load', which is adequate for basic load fl ow calculations but not
much else. Today, the leading packages include much more sophisticated models of wind
turbines, intended for use in fault analysis and dynamic simulations. However, the dynamic
behaviour of wind turbines, particularly those using doubly-fed induction generators (DFIGs),
is very dependent on the detail of the generator control software. The turbine manufacturers
are reluctant to provide these details, which has hampered the development of software simu-
lation models. Some simulation software houses claim to have obtained suffi cient details, but
validation of these models remains an issue.
5.9 Reliability Analysis
The ability of an electrical power system to satisfy the demand with a reasonable probability
of continuity is a measure of reliability. Loss of electricity supply may result in signifi cant
economic and social impact to consumers. Maintaining a reliable supply is therefore of para-
mount importance to electric generators and distributors. The subject of power system reli-
ability evaluation is one that has been studied extensively for traditional generating systems.
The evaluation of reliability when distributed generators are also present complicates the
issues and is a topic that is gaining importance. Distributed generators possess variability that
may be benefi cial; for example their statistical output is correlated to local demand or the
converse, in which case they may contribute disbenefi t under certain conditions. The general
unpredictability that characterizes most RE sources requires that past reliability assessment
techniques based on deterministic principles must be modifi ed to account for the probabilistic
nature of embedded generation. This topic is beyond the terms of reference of this topic, but
more information can be found in Reference [4].
References
[1] National Grid Company (NGC) website www.nationalgrid.com/uk/. In particular, the 'Seven Year Statement'
is very informative and now includes a large section on 'Embedded and Renewable Generation'.
[2] Gross , C. A. Power System Analysis , John Wiley & Sons, Ltd, Chichester, 1986 .
[3] Wallis , E. A. (ed.), Modern Power Station Practice , Volume L, System Operation , Pergamon Press , Oxford ,
1991 .
[4] Jenkins , N. , Allan , R. , Crossley , P. , Kirchen , D. and Strbac , G. Embedded Generation , IEE Power and Engineer-
ing Series 31, Institution of Electrical Engineers , London , 2000 .
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