Power plants alternating emf is generated by rotating

[prudhvi mohan]

In power plants alternating emf is generated by rotating loop in magnetic field which is directly proportional to angular velocity of turbine.I think it is highly impossible to maintain angular velocity of turbine constant(especially in hydro power plants).Then how are they supplying a constant rated current?

 

[Jobrag]

The EMF generated is independent of the turbine speed, all that turbine speed gives is frequency.

 

[prudhvi mohan]

but then how output frequency is held constant ?

 

[SirAskalot]

The grids constant frequency keeps turbine speed constant independent of torque on the tubine. 1000+ other generators share the same load and thus keeps a stable frequency.

If the power plant is not connected to a "infinite bus/grid" but operating alone, the frequency will drop if demanded real power exceeds supplied power.

Keeping a constant angular velocity (within acceptable limits) isn't that hard, big machines with large inertia is pretty stable. Small machines with less inertia can for a few seconds have a speed drop if a sudden power demand is connected. Hydro electric plants are ideal for this, since they can regulate the governor setpoint pretty fast, steam turbines on the other hand have slower regulator speed.

 

[Jobrag]

Have a look at this
http://en.wikipedia.org/wiki/Electrical_generator
Then come back if you have more questions.

 

[Astronuc]

In power plants alternating emf is generated by rotating loop in magnetic field which is directly proportional to angular velocity of turbine.I think it is highly impossible to maintain angular velocity of turbine constant(especially in hydro power plants).Then how are they supplying a constant rated current?

Turbines have governors to adjust the input of energy/torque according to the load.

Large turbines are usually base loaded on a grid, which as smaller gas turbines are used as peaking units because they are ramped up quickly in response to increased load.