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I know that after a sudden generation/load variation there is an imbalance between mechanical power and electrical power at the borders of generators which causes a frequency change according to the swing equation. The first thing that changes is the electrical power (or also the electrical torque) and the governors change the mechanical power (or torque) accordingly to stop the imbalance and so the frequency drop/rise (so the mechanical torque is starting to follow the electrical one.)

I have always studied during my bachelor the transient behavior of a generator considering the electrical torque as constant (like the dashed blue line) but running a generator outage in my simulation tool I noted that the electrical power changes too. One consideration that jumps into my mind is: ok, rotating loads change their absorbed power according to the frequency change so it is true that the electrical power changes, too. The problem is that I imposed the loads as constant power PQ, so there is at least one more cause for the change of the electrical power/torque. What is it? Is it the mechanical power itself that changes the electrical one, too?

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JRE
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  • I think a fault would be defined as a short circuit and modeled as a sudden change in load impedance. The initial impedance would be modeled as the impedance that satisfies the initial complex power. The machine would be modeled as a voltage source and a source reactance that would initially be the direct axis subtransient reactance. I have not studied the transient performance of synchronous machines, There is a chapter in Fitzgerald, Kingsley, Umans Electric Machinery 4th ed. that is intended to provide a basic understanding and an introduction to analysis. You probably need a similar source –  Apr 15 '22 at 14:53

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