By Deron Jozokos with Shoreline Reliability,  LUDECA solutions provider for New England and Eastern New York

I recently helped a customer with an alignment issue they were having on a pump-gearbox-motor machine train.  The problem was that although the machines were aligned within spec,  after a short period of runtime the 16, 500 HP motor shaft began shuttling in and out, or “hunting” for the magnetic center, creating a fear that the coupling would break under the tremendous forces acting on it.  This would in turn shut down the nuclear plant, costing millions of dollars in lost production.  One theory was that the rotor was not level causing it to slide downhill while magnetic forces were drawing it back uphill.  With just a short window of time, the site engineers wanted to level the motor shaft without losing the excellent alignment tolerances.
pump-gearbox-motor machine train
To save time, we measured both machine train couplings simultaneously using the ROTALIGN® ULTRA’s multi-coupling expert level feature. We then used the INCLINEO® system to measure the angle of the motor shaft with respect to gravity.  We verified that the train alignment was still within excellent tolerances (See the ‘As-Found’ condition below) and measured a motor shaft angle of 0.489mils/inch.
As found
Since a hydraulic torque wrench was needed to loosen the 10 total bolts, it was imperative that the number of alignment corrections be reduced to the fewest possible, preferably just one.  Using the measured rotor angle of 0.489mils/inch, we calculated the correction at each foot that would level the shaft and keep the alignment within excellent tolerances.  We input the calculations into the Move Simulator on the ROTALIGN ULTRA to verify our calculations then proceeded with the actual shim corrections.
Alignment and levelness
We monitored the alignment and the shaft angle in real-time with both tools and were able to get the leveling and alignment completed all in a single move (See ‘As Left’ condition below.)
As Left
The millwrights worked as an experienced and organized team and got the shim corrections done quickly and safely.  We finished the job in 1/4 the time allotted and the plant was able to ramp back up to 100% much sooner than planned. Furthermore, the plant reported that the shaft shuttling has stopped.

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, by Ana Maria Delgado, CRL