What are the causes of vibration on gas turbne?

Could be several causes, one of the most common is the rotor plastic flexture. If you leave a long rotor within the machine or outside and don´t rotate on a regular basis, it will bend and when installed, it will develop vibrations.

The rotors tend to flex under their own weight and if left unnatended enough, this flexion could be permanent so it is highly advisable to rotate them ia 180º pattern.

1 foundation Bolts  & grouting problem

2 misalignment & casing bolts loos or broken 

3  turbine bearing wear tear due to lubrication failure 

4 uneven burning due to air  fuel  ration 

5 turbine & compressor rotor  blades damage  

6 due to  generator  load variation & turbine run at over  speed 

7 rotor bends or Bow 

8 rotor balancing  issue 

9 Exhaust pressure  issue  

There are many causes but most common are these

Missallignment 

Loosing of Foudation Bolts

Rotor Unbalancing

Wear tear of rotating part

Bearing Problem

bad shaft alignment and bad flame dynamics 

Please be aware of the natural frequency of the rotor. I mean wheather the equipment is running above the first critical speed. so always there may be high vibration while the machine croses its natural frequency.