# Question on power plant generators

## Main Question or Discussion Point

I'm trying to understand exactly how power plant generators increase power output. So I will explain what I think is right.

To increase the power output of a generator more torque from the prime mover is required to increase the torque angle between the voltage impressed on the stator from the grid with the voltage impressed on the stator from the rotor field. As the torque angle increases up to 90 degrees the two voltages will be more in phase and be additive which will result in a larger amount of current produced in the stator. Thus increasing the power output.

Can someone correct me, and what happens with the phases between the voltage and current when the torque angle is increased. Is there still a lagging power factor or does the current align with the sum of the two voltages.

I'm probably wrong in my thinking but some clarification would be very much appreciated.

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turbo
Gold Member
You might want to spend time studying steam turbines. In power plants, power output can be increased or decreased by adjusting the pressure-drop across the turbine, including auxiliary systems like steam-hoggers and condensers that allow the steam to exit the turbine at lower than atmospheric pressure. Good luck with your studies.

Sorry but I'm more interested in the electrical side of it and less on the actual mechanical side of the operation. I have been trying to find info in the internet but so far not successful.

jim hardy
Gold Member
2019 Award
Dearly Missed
You have it pretty nearly right.
The phase of the current is largely affected by the excitation, and what the load will accept.
Power plant generators are all in parallel so can exchange lots of imaginary(out of phase) current.
You haven't said whether you're assuming constant field or constant terminal volts....
The sad truth is the voltage regulator gets into the act and controls excitation.

Here's an animation I found with a quick Google search:
http://www.ece.umn.edu/users/riaz/animations/syncmotpd.html

It's for a motor, but only difference is sign of torque and in-phase current.

We had some interesting threads a couple years ago with a really cool student named Bassalisk.

May you find them interesting, or a cure for insomnia.

Do you have a machinery lab in your school? It is a lot of fun to watch the angle of a shaft with a strobe light synchronized to terminal voltage. And it gives you that "feel" for what is going on.
http://www.ece.umn.edu/users/riaz/animations/smswing.html

old jim

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