During commissioning of a cogeneration plant the air cooled generator cannot be run up to
synchronization speed because of high 1X vibration during startup. Several attempts were
done by the commissioning team to balance the rotor but proven ineffective. This paper
presents the vibration analysis performed by GE MDS Engineer. As a result of the analysis
it was concluded the high levels of synchronous vibration are caused by thermally induced
bow because of rub in the new type of seals installed in generator casing. The seals were
removed for test and the generator was started successfully. The next part of the paper
discusses the differences between Newkirk and Morton type thermally induced bows as they
can be observed in the machinery diagnostics during field analysis.