Transient Stability During Asymmetrical Faults
This research project has been conducted at RTE in order to study the transient stability after
asymmetrical faults. When three-phase short-circuits occur in a network, almost all the electrical
power is lost on the relevant line(s). Among all short-circuit types, it is the most drastic event and the
issue has to be solved very quickly. But oddly, it is also the easiest problem to solve mathematically
speaking. This comes from the fact that the system stays balanced, and equations can be simplified.
However with line-to-ground faults this is no longer the case, and transient stability analysis becomes
Until now, unbalanced situations have not been studied much. Since this kind of trouble is less
serious than losing all three phases, every protection devices on the network have been sized to
counter three-phase faults in time and avoid severe consequences. They will then also work for onephase
Despite this, there is a desire from RTE to understand
– physically and mathematically – what
happens when one-phase faults occur, and it is the mission behind this master thesis. First, a
mathematical theoretical model was derived to examine a
network’s stability without running any
simulation. Then, once simulation software programs were taken in hand, several tests were run on a
very simplified network, and compared with the theory developed previously. Finally, these
experiments were carried out on a much larger scale.
It is important to understand that, except for the theoretical model, all the results and conclusions in
this document come from simulations. Even if a lot of tests and models led to them, these
conclusions must be handled with care. The goal of this work was also to have a better
understanding of unbalanced systems, of the Fortescue representation and thus, understand more
clearly the parameters required by simulation tools like Eurostag© for future studies.
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