Balancing With the Presence of a Rub

During commissioning of a cogeneration plant the air cooled generator can not 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. Article 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 article discusses the differences between Newkirk and Morton type thermally induced bows as they can be observed in the machinery diagnostics during field analysis