I am unsure about how to word this question properly and I assume that it might take two directions probably because of the unknown variables involved but here goes...

On the actual physical power generator in a coal power station...

  1. How much force does it take to start to move the generator shaft from a "stationary/motionless" state?
  2. How much force does it take to to keep the generator moving at the required speed after it reached that speed already?

I am ignorant about the dimensions of these generators so this might turn into a "how to calculate" answer unless someone knows more about the actual generators used in the industry.

  • $\begingroup$ I don't know how much but I've spun a power turbine by hand, it wasn't particularly hard. It was a journal bearing, tho, so not recommended to do this much. Running torque would be probably 5-10% more than electrical output equivalent. $\endgroup$
    – Tiger Guy
    Commented Aug 2, 2022 at 18:26
  • $\begingroup$ The trouble with this question is all coal power stations are different. They have different capacities & different sizes of equipment & newer stations may have different types of equipment to older stations. The best you can hope for is for someone to tell you how to calculate the numbers you are asking about, $\endgroup$
    – Fred
    Commented Aug 2, 2022 at 23:14
  • $\begingroup$ Dinorwig, they keep the rotors spinning using power until they need to generate then they get full output in about 6 seconds, not possible from stationary. $\endgroup$
    – Solar Mike
    Commented Aug 3, 2022 at 6:43

2 Answers 2


It is common practice to "motor" a turbine/generator assembly slowly in the absence of steam or water flow, while maintaining full lubricating oil pressure, so the sheer weight of the blade wheel and rotor do not deform the bearing surfaces while the system is off-line. So, the system almost never comes to a complete stop.

The process of bringing one of these fully on-line takes many hours of slowly bringing up the temperature and rotor speed so all parts of the system are at the same temperature at every step of the process- all while carefully monitoring oil pressure, torque, and temperature in hundreds of spots.

This means that a meaningful answer to your question will be hard to get because the power-up process is not power-limited (i.e., turbine torque x RPM).

If you did know the rotary inertia of the whole shebang, and the stall torque of the turbine disc at full steam flow conditions, you could in principle solve for the angular acceleration rate- but the system would never, ever be operated in that manner.


The turbine is not the generator. So you could be asking about the generator on its own or the turbine linked to the generator. Assuming you are asking about just the generator:

  1. You can't know this without knowing really specific things about the generator because this is about static friction which is related to the exact construction rather than their fundamental theory of operation.
  2. This is just $\text{Power} = \frac{\text{Torque} \times \text{Angular Velocity}}{\text{Efficiency}}$, (sort of) neglecting the friction from #1
  • $\begingroup$ I was assuming that the device applying the force would automatically not be included in the equation. In this case the turbine. $\endgroup$ Commented Aug 2, 2022 at 13:50

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