AC Generator Cooling Air Flow

hi all,

i am working on ac generator 100kva 380v 3phase 50hz, the engine is perkins but the generator is italian made. when i open it and took out the main rotor, i noticed that there is plastic round closing at the exciter side and its opened from the middle size same as the generator rotor, the rotor goes through it, the cooling air will go through this opening only, the plastic was tied to the main stater winding with some tie wraps.

i asked the owner of this genset and he said no repairs was done on this generator and he bought it as new set since year 2000, in other meaning this plastic was fitted in the factory but as it tied to the main stater winding with tie wraps i dont think so, i dont think they will fit it this way in the factory.

my question is: should this plastic closing be there or not ? with this plastic fitted, the cooling air will not flow behind the stater winding but only through the rotor side! is it normal or should i remove it ?

please advice me guys if some one has an idea?

thanks