Explain the working principle of induction generator?

Answer 1

what i do then i press emrjancy batten in generator

Answer 2

its an induction motor rotaes at a speed above the synchronous speed nr>ns. and it needs reactive power for its excitation which supplies by the grid or by connecting capacitor bank in parallel with the stator (self excitation). self excitation technique uses in stand alone generator or to keep the the power factor of the grid when its connected to the grid.for successful self excitation process the stator windings should have residual magnetism to produce voltage  output.