# Is it require to run fault on every branch in the model and determine the stability of the generator?

Hello All, I have a task to run 3-phase fault on every line that is over 100 kV in the footprint of the Transmission Operator and determine if the generators near by the line will be stable or not.

My questions on this task are below: 1. Why is it necessary to run the analysis on every single line? Isn't it the case that generator is more severely impacted by the 3-phase fault on the lines exiting from Generator Step Up Transformer (GSU) than the fault on any other line that is far away from the generator in the network? In other words if the generator is stable for a 3-phase fault on the lines connected to GSU then can't we say that the generator will be stable for 3-phase fault on any other line farther away from the generator.

1. Will there be a case where the generator (assumingly a big generator) is stable for a 3-phase fault on the line next to it's GSU but a small generator which is electrically close to the big generator is not stable for the same fault?

1. If the reasoning in #1 is correct then it will greatly reduce the channels (in other words number of buses and parameters that I need to monitor will be limited to just 3 buses around the generator) that I need to monitor and save and thereby reduces the time taken to perform transient stability analysis of the entire network.

2. I understand that impedance of the network during the fault also plays key role in determining the stability of the generator and I believe that limiting the analysis just to the lines connecting to GSU is sufficient.

3. Is there something else that might impact this approach or something that I'm missing in my analysis?

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If rotor angle stability is the issue here then it is sufficient to just add system angles statistics channels and monitor the angle spread in each simulation.

If any generator goes out of step in the simulation the angle spread will increase. Angle spread is therefore a good indicator of rotor angle instability. If angle spread is high (<300-400 deg) the bus number of the most unstable generator is seen in the channel with bus number of maximum rotor angle.

It is thereby possible to identify unstable generators without adding channels for individual generators.

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The task should require: "run 3-phase fault on every line that is over 100 kV in the footprint of the Transmission Operator and determine if EACH generator will be stable or not."

In dynamic studies, anything is possible, as far as unexpected results is concerned. A fault away a generator X could be severe enough such nearby generation or load trips and the network reach a weaker state or even worse, a cascade condition could occur.

I recommend that at least once, run an exhaustive fault test over the whole network, and identify/rank each fault effects on the system response. Some faults causing minimal effects on the network could not be run the next time. Using parallel processing will help reduce study times.

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