Solving the Challenge
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. The relative shaft vibration at the generator non-driven end bearing was measured to be close to trip level and therefore a root cause analysis was initiated by Alstom to solve the problem.
Alstom sought Waukesha’s expertise to design and manufacture new bearings to resolve the spiral vibration and fit within an existing radial space to provide a drop-in replacement without modifications to the pedestal.
In terms of performance, the new bearings were required to have maximized stiffness coefficients, in particular in the direct coupled horizontal plane. Within the space constraints of the original fixed geometry bearings, the new design would need to produce acceptable load support and oil inlet flow velocity, with double insulation to prevent grounding of shaft currents via the bearings.
Waukesha Bearings engineered a Maxalign journal bearing with a 400 mm (15.75″) inside diameter to solve the challenges on this turbo-generator.
Using proprietary predictive tools coupled with 30 years of field experience, testing, and development, Waukesha was able to confidently predict bearing performance. This included optimization of pad geometry and lubrication method, as well as taking advantage of the superior stiffness qualities of the company’s patented ball and socket pivot design.
The installation successfully eliminated the vibration and shifted critical speeds to well above the rated speed, just as the performance testing predicted.