There are numerous advantages to high-speed balancing of generator and turbine rotors. These include:

  • Smooth operation through the entire speed range up to overspeed.
  • The ability to access optimal weight planes, which are not normally accessible during operation in the machine.
  • Verification of the mechanical integrity of the rotor and any assembled components—up to overspeed.
  • Electrical testing of generator rotors through their entire speed range can identify the existence of any speed related electrical faults.

Also, long and slender rotors may not be able to be balanced with the planes available in the field due to the reduced influence of these areas on the unbalance in the rotor.

What rotors are particularly suited for a high speed balance?

In general, rotors that have had a change in their mechanical condition are best suited for a high speed balance. The following list identifies some of these mechanical changes that have benefited from a high speed balance:

  • Changes made to the centers of rotation (also known as throwing journals).
  • Generator rotors that have been completely rewound.
  • Generator rotors that have been significantly disassembled, such as removal of retaining rings and some coils.
  • Rotors that have had vibration problems produced by and/or repaired for the following reasons:
    • Permanent bowing due to rubs or water induction
    • Loss of mass due to rubbing or other means
    • Cracking
    • Thermal Instability
  • Turbine rotors that have been re-bladed, especially if the blades were not moment weighted.
  • Turbine rotors that have had significant blade repairs.
  • Rotors that have had their journals, couplings or fits machined.

In general, long and slender rotors are the most well-suited for a high speed balance, but any rotor that has the aforementioned repairs or problems can benefit from high speed balancing.