In-situ trim balancing

Rotors are normally balanced at low speed (400 r/min) and weight adjustment made in two convenient planes, one at each end of the rotor. This adjustment may be by varying screwed plugs in tapped holes, or by adding balance weights at specific circumferential positions. Often after the rotor is balanced at low speed and installed in the machine,  imbalance is detected when the turbine is run up to full speed (6000 + rpm).  An in situ trim balancing can be carried out to take out any calculation errors that are very often made during low speed balancing.