In its simplest form an induction generator is simply an induction motor that is rotated above synchronous speed. Unlike a synchronous generator, the field in the rotor is created by drawing large amounts of reactive current from the line.
Synchronization is automatic because line frequency is applied to the stator once the prime mover has accelerated the rotor to near synchronous speed. Remember, unlike a synchronous generator, there is no rotating field on the rotor until it is attached to the grid so the normal matching of voltage, phase angle and speed is reduced to speed alone.
The fact that there is no field until grid connection (and hence no voltage produced) also means that an induction generator is generally incapable of isolated operation, though there are special designs involving capacitors at the terminals, but that is a totally separate topic.
The rating is limited by the size of the prime mover and the ability of the grid to supply the significant inductive current required for excitation without creating destroying the grid voltage profile and/or creating instability.
Another issue to be aware of: induction generators operate at variable speeds, function of the slip-torque characteristic of the machine. This means that the shaft speed of the induction generator will vary with the active power output of the generator and even with the voltage at its terminal. Therefore, make sure that the steam turbine is capable of working at off-nominal frequencies.
Induction generator mostly works in wind energy generation, induction generator synchronizing with gird by soft starter with help of PLC. When induction generator start rotating its draw reactive power from grid to create magnetic field on its starter, its draw power from grid until machine goes in generation, when machine goes to generation, the PLC match voltage and frequency to grid of alternator. If parameters match by pass contactor closed, these smooth operation done by soft starter.