Excitation winding and fuction of AVR

[mars shaw]

I have a generator.
Single phase
220 volt A.C output
Frequency 50 Hz
2000 kVA

Rotor winding of my generator was burnt.
It was rewinded but it burnt again after 1 day.
There are 2 types of windings in stator one main winding which gives 220 volt A.C output and 2nd is excitation winding which is giving 135 volt A.C to AVR and then AVR is giving about 80 volt D.C to rotor winding for excitation.
But mechanic says that excitation voltage that are abtain from excitation winding to AVR should be about 70 volt A.C and the D.C voltage which is given to rotor from AVR should be 18 volt D.C.
According to him main winding and rotor winding are short to each other so that's why excitation winding is giving high voltage.

Now in this situation I think AVR is exciting the rotor after regulating voltage and main output is still 220 because of AVR.
But AVR is between excitation winding and rotor winding so it shoult burn first. Why rotor winding is burning again and again?
Now where is the fault in AVR, stator winding, excition winding or complete stator winding.

 

[mars shaw]

sorry it is 2kVA