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Simplification algorithms for large-scale power system transmission grids

Kruijer, Tomas
Master thesis
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URI
http://hdl.handle.net/11250/2368104
Date
2015
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  • Institutt for elkraftteknikk [2669]
Abstract
The simulation of large-scale power system models including transmission grid

representations is limited by available computation power and time. Therefore, the

reduction of transmission grid models is of paramount importance. This report proposes and

tests a new method of reducing power grids. This method allows to reduce an existing

transmission grid model to any desired size, however, at the cost of accepting increasing

levels of inaccuracy.

An algorithm is developed that reforms the total number of nodes in the full grid

representation into a smaller number of clusters, which are then connected by equivalent

power lines. The algorithm is designed in such way that those power lines remain in the

transmission grid that are likely to form a bottleneck, thus restraining power flows.

The accuracy of this method is measured by comparing the power flows in the reduced

power grid to the flows from the original grid. The power flows of the full and reduced

model are calculated by applying linear approaches based on PTDF matrices. PTDF matrices

are commonly used in transmission grid analysis, linking node injections to power flows. The

power flows are calculated based on a pre-defined set of injections, which represent cases of realistic power plant dispatches. The PTDF matrix for the reduced matrix is derived with the method proposed by Shi et al. The reduced matrix is operating point dependent, based

on a set of reference injections.

The results show that every country can be reduced up to 37.5% of its original size, when

maintaining an allowable error of 20% of the available transfer capacity of a power line.

Most countries can even be reduced further before they exceed the set accuracy

benchmark.

In addition to this, the report researches whether guidelines can be identified to which

extend power grids can be reduced within preset limits of accuracy. Power grids in countries

have different properties like topologies and grid characteristics, possibly leading to differing error behavior. The results show that no clear relation can be identified between the properties of a country s power grid and its error behavior, but is dependent on case specific situations in which node injections play a particularly decisive role. As the node capacity and node generation are random though, so are the occurring errors.

Finally, the relation between accuracy and gained computation time in optimization

simulations is identified. The relation between the number of variables in an optimization

model and required computation time is exponential. This relation shows that without

exceeding the preset boundaries of accuracy significant gains in computation time can be

acquired. A grid reduced to 22.5% of its original sizes does not exceed the error limit in

power lines, while the computation time reduces by a factor of 261.
Publisher
NTNU

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