Turbine speed remains constant at rated speed once the m/c is synchronised....during change in load the governer issues command for opening/closing of nozzle/deflector which means mech. i/p (water/steam)to the turbine is varied accordingly.....however the turbine speed has to remain at rated speed despite the mech. i/p....the question is how does the load(power o/p) vary at constant rated speed???

To answer your question: There's more to power than speed alone. There's also torque. When the load increases, the mechanical input to the turbine increases to add more torque.

If you look at the attached generator, you will see a change - not in speed, but in pole angle - and in current, of course.

Power = rotational speed times torque. If rotational speed is constant and power increases, the only factor that can change is the torque. And that is exactly what happens.

After sync the generator is locked to the grid and the grid maintains the speed. The governor responds to speed changes and there should be no speed changes when sync'ed to the grid. The governor may be placed in droop mode and then used to set power supplied to the prime mover. A smaller machine on the grid will usually be running at a fixed power output and the governor does not control except to set the throttle opening and to prevent a runaway in the event of a load loss.
PS
Hi kixs84;
Skogs speaks several languages fluently including Boolean.
However I don't think that he is fluent in tx. We do our best to overcome the language barriers inherent in an international forum but not many of us older members are NOT comfortable communicating in tx. Can you repost in English with capitalization?/Safety valves

In a synchronous motor/generator, the torque on the rotor is proportional to the sine of the angle between the magnetic fields of the rotor and stator -- think of the rotor as a glorified compass needle. In reasonable zones of operation, this is close to being proportional to the angle itself. So as waross points out, the effect is analogous to that of a spring or elastic band.

If you want to analyze this more formally, the angle will be proportional to the arcsin of the torque, and at constant speed, to the power.

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