how does the steam turbine generatorsmaitain constant velocity with the changing load conditions

Dear Sushmita,

I only saw ur discussion board now, and I find U have received many clarifications....I will agree with what Mr.balasubramanya, of KIOCL Ltd: has written....there is a Mechanical accessory called the Governor' and an Electrical one called the 'AVR' which 2gether carry out the function of Speed-Control...regards....Sushil kumar.

steam turbine when not connected to grid rotate freely without any load tx by generator. in such case we can increase the speed of turbine upto any value, limited by any overspeed trip paramaters like 10% of the normal 3000rpm.

in case when we are connected to the grid, grid acts as a load where we can transfer the power at constant voltage and constant freq. we can transmit power upto our capacity (like capacity of 200MWe any plant say X) limited by the capacity of grid as a load. now the question is how much we can transmit.

now prime mover is steam and excitation to synchronous generator is provided via some excitation system. as synchronous gen is connected to the grid, it will rotate at given frequency (freq limited by load in grid, more is freq less is load and vice versa). if you go through the phasor diagram of the generator, Ef= Vt + IaXs
 where Vt is terminal voltage (output of genrator proportional to grid voltage) Ef is excitation voltage and Ia is armature current and Xs is armature resistance.

Ia is power limiting factor and remaining factors are constant.

as P = Vt* Ia cos@

@ will decide whether excitation is inductive or capacitive and can be adjusted to lagging power factor so as to avoid end heating of stator.

so @ is decided.

Vt is constant

so P is proportional to Ia, which is is decided by prime mover ie steam, rotating the rotor at fixed speed

torque is equivalent to force*distance

hello madam

the velocity of the turbine is maintained constant at all loads through the governor of the turbine.this governor is inturn controlled by an automatic voltage regulator or simply AVR.when there an increase in load the voltage drops anr AVR makes the govrenor to supply more steam to maintain constant voltage and vice versa.on no load there is no drop in voltage so the generator runs at rated speed.as the system works on closed loop system the generator will not overspeed.

Its a good question you have asked Mr.Geoffrey. I truly have a very faint idea on steam turbines but I'm sure my friends on this platform will help you out.