Specialty: Quill shaft Replacement
Applies to: MS5001 and 6001 GE gas turbines

GE gas turbines like the models listed above have reduction (load) gears.  The turbines run at approximately 5100 rpm at rated speed.  A speed reducer is required to operate the generator at synchronous speed (for 2-pole generators that would be 3600 rpm) to generate power at 60 cycles per second.  A typical reduction gear is shown below in Fig. 1 (2 views).

Fig. 1: Two views of a typical Reduction (Load) Gear

There are two gears inside the gearbox: a high-speed pinion gear and a low-speed bull gear.  Inside the bull gear, there is a special “quill shaft” that protects the gearing against inadvertent synchronizing of the generator to the power grid “out of phase.”  If an event of this nature occurs, the quill will likely “twist,” resulting in an out-of-roundness condition.  However, the gears will be protected.  The result, however, will be a high-vibration condition that can only be rectified with replacement of the “quill shaft.”

Fig. 2: Bull Gear with Quill Shaft Installed

Knowledge of how to properly disassemble, inspect, check for runout (twist), reassemble and align should not be entrusted to inexperienced engineers or untrained millwrights.

Fig. 3: Quill Shaft removed from Bull Gear

The alignment process for reduction gears having a “quill shaft” is very complicated.  The quill drop check, bearing centralization check and generator rotor/bull gear “crank” check are crucial to proper alignment and for the 3-bearing set. 

Fig. 4: Alignment procedures for various model reduction gears

For the best results, we suggest you contact Pond and Lucier, LLC so that an experienced engineer with the correct alignment data can be sent to technically advise during the change out of the quill shaft.