by Jessica Whalen and Richard Livermore-Hardy. Published in International Power Engineer, May 2010.
By Richard Livermore-Hardy, Waukesha Bearings
Published in Turbomachinery International, July/August 2014
An Alstom 450MVA hydrogen-cooled generator operating at 3,600 rev/min and equipped with a brush gear unit showed spiral vibration with a forward rotating unbalance vector.
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.
Potential modifications were studied by Alstom using hot spot stability analysis with a rotor dynamic model of the generator rotor, and bearing supports. Based on the calculated results, a modification of the generator shaft line was implemented using tilting pad radial bearings at the generator non-drive end and exciter end locations to shift the slip ring shaft critical speeds well above the rated speed.
Read the article in the July/August 2014 issue of Turbomachinery International.
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 Power identified a phenomenon of spiral vibration close to the trip level on one of their 450MVa hydrogen-cooled generators, our proprietary predictive tools and extensive industry experience on equipment of this size made Waukesha Bearings 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.
In the May 2010 issue of International Power Engineer, Jessica Whelan and Richard Livermore-Hardy look at new large tilting pad radial bearings designed to further improve safety margins.
It is difficult to pick up an industry publication without seeing an article or viewpoint covering the trend away from coal toward natural gas as part of the global power generation mix.
Whether climate-change legislation happens this year, in 2011 or in 2020, project owners and financiers at the very least are ‘cautious on coal.’ This shift toward cleaner energy is creating increased focus on alternative fuel sources; nuclear energy and the many forms of renewable energy are the targets of technology development, investment and new business ventures.
However, in the short to mid-term, natural gas-driven power generation is the obvious substitute for coal as the economy recovers…as GDP grows, so does the demand for energy.
This move toward natural gas as a primary source of energy has placed new demands on the makers of gas-fired combustion turbines. Larger, lower emission, and more reliable and efficient machines are required if turbines are to play a more vital role in the global power mix.
In anticipation of these market demands, Waukesha Bearings, a leader in hydrodynamic bearings and magnetic bearing systems, has developed the next generation of large tilting pad radial bearing designs to further improve safety margins and provide superior performance to address the challenges associated with these machines.
The next generation technology was applied to Waukesha’s existing ball and socket tilting pad radial bearing with Directed Lubrication, which has been used successfully over the past 25 years in large frame gas turbines, steam turbines and turbo-generators. Throughout the development cycle, Waukesha engineers worked closely with leading original equipment manufacturers to translate turbine performance requirements into improved bearing designs using a combination of field experience, testing and advanced analysis techniques.
In order to directly address requirements for improved machine efficiency, Waukesha’s latest design uses an efficient 4-pad arrangement to minimise power loss and reduce the number of components.
As a result of the trend towards larger machines, higher bearing loads and surface speeds, the design also includes an optimised pad and hydrostatic jacking groove design to further reduce pad temperatures, leading to increased safety margins and machine reliability.
The latest technology compliments Waukesha’s proven ball and socket pivot design, which, due to the proprietary design and materials, has excellent dynamic alignment capability typically required on ‘hot’ machines during the transition from cold to hot conditions plus high stiffness for assured bearing dynamic characteristics.
Waukesha engineers used proprietary predictive tools and testing to design and verify the performance of the next generation of large tilting pad radial bearing designs, which have now been in service for several years on numerous gas-fired combined cycle turbo-generator applications.
The knowledge gained during this process will allow Waukesha to further adapt their technology for the ever increasing requirements for improved performance and reliability in the gas-fired power generation market.