what is the reasons of increasing vibration ?
why increasing of MVAR increases the vibration ?  

        

           HELP SYRIA

the copper in the field must be able to expand with the tempurature changes from IR.  Changing MVAR would be changing current in the field

It is possible that one of the copper bars (turns) is not doing so from the designed fixed point and thus changing the center of mass.

It could also be posible that the rotating forging that holds the copper bars has a localized area with different materal charecteristics to the majority, thus being a thermally sensitive rotor and developing a slight bow with tempurature

I have experance expnading end turn that would cause extreme vibration if VARs got excessive and vibration would not dimenish with reduction of field current.  the unit could be returned to turning gear, the end turn reseat without centrifical and return to operation with acceptable vibration

A shorted turn on the rotor can cause a thermal bend due to differential heating of the rotor forging. As the excitation current increases the vibration typically worsens, but not always.

Can you trend vibration against excitation current? There is a long thermal lag due to the mass of the rotor forging, so you may well see a change in vibration develop over a period of time following a change in excitation.
  

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