The generator doesn't hunt.
The generator prime mover's governor will hunt if not properly tuned. And we're supposed to be talking about properly acting governors. Not laboratory exercises.
When your plant is connected to the grid, if you start a large motor the grid will supply that power until such time as your operators increase the power produced by one or more prime movers to return the export to 2-3 MW. In fact, if one of the turbines trips, won't the refinery continue to run on grid power? (Even if there is some load-shedding scheme in place/required?)
When you are connected to a sufficiently large grid, there is no difference between turbine frequency and grid frequency. Your little 25 MW unit isn't likely to have much of an effect on a 2000 MW grid, or even a 1000W grid, or even a 600 MW grid. The frequency of all the machines connected to the grid is the same--because they are synchronous machines. Synchronized together.
Even on a grid composed of two 25 MW machines, the speed of both machines is identical and is directly proportional to the frequency. And if the power produced by the two machines isn't equal to the power being consumed by the load, then the frequency isn't going to be at rated.
Full stop.
The question remains: How much does the speed of the turbines at your site change when they are loaded while connected in parallel with a other machines on a grid of relatively stable frequency? Even if the frequency isn't 50.0 Hz, how much does it change when you increase the fuel to one of the turbines causing it to accept more of the load on the grid? And for how long does the speed change?
The generator prime mover's governor will hunt if not properly tuned. And we're supposed to be talking about properly acting governors. Not laboratory exercises.
When your plant is connected to the grid, if you start a large motor the grid will supply that power until such time as your operators increase the power produced by one or more prime movers to return the export to 2-3 MW. In fact, if one of the turbines trips, won't the refinery continue to run on grid power? (Even if there is some load-shedding scheme in place/required?)
When you are connected to a sufficiently large grid, there is no difference between turbine frequency and grid frequency. Your little 25 MW unit isn't likely to have much of an effect on a 2000 MW grid, or even a 1000W grid, or even a 600 MW grid. The frequency of all the machines connected to the grid is the same--because they are synchronous machines. Synchronized together.
Even on a grid composed of two 25 MW machines, the speed of both machines is identical and is directly proportional to the frequency. And if the power produced by the two machines isn't equal to the power being consumed by the load, then the frequency isn't going to be at rated.
Full stop.
The question remains: How much does the speed of the turbines at your site change when they are loaded while connected in parallel with a other machines on a grid of relatively stable frequency? Even if the frequency isn't 50.0 Hz, how much does it change when you increase the fuel to one of the turbines causing it to accept more of the load on the grid? And for how long does the speed change?