By Richard Livermore-Hardy, Waukesha Bearings
Published in Turbomachinery International, July/August 2014

An Alstom 450MVA hydrogen-cooled generator operating at 3,600 rev/min and equipped with a brush gear unit showed spiral vibration with a forward rotating unbalance vector.

Spiral vibration, also known as the Newkirk effect, can be observed on various types of turbomachinery and is caused by a vibration-induced hot spot on the shaft surface generated by friction.

Potential modifications were studied by Alstom using hot spot stability analysis with a rotor dynamic model of the generator rotor, and bearing supports. Based on the calculated results, a modification of the generator shaft line was implemented using tilting pad radial bearings at the generator non-drive end and exciter end locations to shift the slip ring shaft critical speeds well above the rated speed.

Read the article in the July/August 2014 issue of Turbomachinery International.