-We verify and examine criticality in a 1000 bus network with an AC blackout model that represents many of the interactions that occur in cascading failure.At the critical loading there is a sharp rise in the mean b l a c kout size and a power law probability distribution of blackout size that indicates a s i g n i f icant risk of large blackouts.

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This paper details a methodology for investigating the reliability of different offshore grid design options for the connection of offshore wind power to shore. The methodology uses a sequential Monte Carlo based technique that allows investigation of realistic offshore phenomena such as the weather dependency of component repair times. A number of case studies are examined for the connection to shore of a cluster of far offshore wind farms and a cost benefit analysis is performed which compares the capital costs, electrical losses and reliability of each. There is shown to be clear value in options that have inherent redundancy and alternative protection strategies which avoid the use of expensive DC circuit breakers are shown to be potentially viable. It is also found that low probability, high impact faults such as transmission branch failures are a key driver behind overall grid reliability.

Power systems are operated with some margin of security to ensure that the most likely losses of plant will not cause interruptions to supply. However, this security margin has a cost that may not be justified by the benefit in terms of prevention of lost load. The authors argue that the level of security could be set on the basis of a cost/benefit analysis that balances the cost of operating the system against the expected outage cost. The expected outage cost is determined using a Monte Carlo simulation of the system operation in which random outages are simulated. Such a simulation should not be limited to small but relatively frequent outages but should also include major disturbances that affect a large part of the system. In order to achieve a sufficient degree of accuracy, the simulation models the actions taken to save the system during emergencies, the duration of the restoration process, and possible protection malfunctions. It is shown that sympathetic trippings due to protection malfunction can have a very significant impact on the probability of major incidents and hence on the value of security