Transient Stability During Asymmetrical Faults

University essay from KTH/Elektroteknisk teori och konstruktion

Author: Nicolas Couturier; [2015]

Keywords: ;

Abstract:

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

tricky.

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

problems.

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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