Maxalign® Bearings Reduce Spiral Vibration on Turbo-generators
With over 100 years of experience, Alstom Power is a leading provider in the power generation industry. Close to 25% of the world’s power production capacity depends on Alstom technology or services. With the industry trending toward improved efficiency, in both new and existing equipment, higher demands are placed on the equipment and the bearings.
When Alstom identified a phenomenon of spiral vibration close to the trip level on one of their 450 MVa hydrogen-cooled generators, Waukesha Bearings’ proprietary predictive tools and extensive industry experience on equipment of this size made us the clear choice to design and manufacture a drop-in bearing replacement.
More than 13 generator sets have been commissioned since the initial phenomenon was detected in 2003. In total, the Maxalign bearings have seen 600,000 cumulative operating hours with these particular Alstom generators.
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.
The Maxalign design offers additional benefits to OEMs and end users alike. The ball and socket pivot design is highly adaptable to shaft misalignment caused by mechanical loading or thermal effects in large rotating equipment. The ball and socket pivot design eliminates pivot wear commonly associated with traditional pivot designs, thus providing a zero maintenance bearing.
In addition, Waukesha’s ‘Directed Lubrication’ reduces the amount of oil needed, reduces power loss, and keeps operating temperatures within the acceptance range.
Hydrostatic jacking grooves in the lower pads not only reduce friction during start up but increase safety margins and machine reliability. The bearing also includes a provision for instrumentation to match original equipment fittings as well as the ability to directly measure electric resistance of each insulating layer when assembled.
Overall, the benefits point to an increase in availability and reliability in the field.
Maxalign Bearing Advantages
- Phenomenon of spiral vibration eliminated
- Critical speeds shifted to well above the rated speed
- Drop-in bearing replacement for fixed geometry bearing without pedestal modifications
- ‘Directed Lubrication’ controlled oil usage and power loss and achieved acceptable temperatures
- Ball and socket design provided superior stiffness and dynamic alignment capability
The Maxalign Bearing
The first Maxalign bearing was installed in 1983, in a 130 MW turbo-generator application to overcome a new misalignment condition. Since then, Waukesha Bearings has provided more than 150 different Maxalign designs in over 2,000 applications for turbo-generator, gas turbine, steam turbine, and synchronous clutch OEMs. The Maxalign bearing is a proven, versatile design available from 300 mm (11.8″) upwards and in combination with thrust bearings, giving customers the benefit of a complete machine set.