The doctoral dissertations of the former Helsinki University of Technology (TKK) and Aalto University Schools of Technology (CHEM, ELEC, ENG, SCI) published in electronic format are available in the electronic publications archive of Aalto University - Aaltodoc.
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A Method for the Probabilistic Security Analysis of Transmission Grids
Liisa Pottonen
Dissertation for the degree of Doctor of Science in Technology to be presented with due permission of the Department of Electrical and Communications Engineering for public examination and debate in Auditorium S4 at Helsinki University of Technology (Espoo, Finland) on the 8th of April, 2005, at 12 o'clock noon.
Dissertation in PDF format (ISBN 951-22-7592-9) [1440 KB]
Dissertation is also available in print (ISBN 951-22-7591-0)
Abstract
This thesis proposes a probabilistic method for evaluating transmission grid security after line shunt faults. The most efficient contributions to system reliability enhancement can be found in probabilistic methods applicable to real transmission grids. One aim of the research was also to get an estimate of the Finnish 400 kV transmission grid reliability.
The method developed in this thesis takes into account the effect of the following issues: frequency of line faults, fault location on the line, protection system, different substation structures, failure rates of substation components and the dynamic behaviour of the power system after different contingencies.
Mathematical modelling and computational methods were used in this research. Statistical analyses for the estimation of initiating events such as line faults were made. A failure mode and effect analysis was made for substation components using both the Finnish 400 kV device-failure database and expert judgments. Reliability analyses for substation post-fault operations were made with event and fault trees. Different event tree end states (fault duration and circuit breaker trips) were then simulated with a power system dynamic analysis program using a particular load flow and grid topology. The dynamic analysis results were classified as secure, alert, emergency and system breakdown. A special alert case 'partial system breakdown' was also classified. The event trees were then reanalysed, now focusing on the power system states rather than the substation consequences.
The method was applied to the Finnish transmission system and some quantitative estimates for grid reliability were obtained. Several grid-level importance measures (Fussell-Vesely, risk decrease factor, risk increase factor and sensitivity of parameters) for substation components and model parameters, as well as estimates of the total and partial system breakdown frequencies, were calculated. In this way, the relative importance of the substation components regarding the total and partial system breakdown was reached. Contributing factors to partial and total system breakdown after line faults were also found and ranked. On the basis of the results, some recommendations for improving the transmission grid reliability, in terms of maintenance planning and investments, were made.
Keywords: transmission grid, power system, security, reliability, substation, protection, importance
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© 2005 Helsinki University of Technology
Last update 2011-05-26