Reduction of Damaging Stator Core and Winding Vibrations in Large-Diameter Salient-Pole Synchronous Machines
Is it possible to substantially reduce harmful vibrations and noise caused by less-than-adequate electrical design of the stator winding and core without replacing major components?
Need and Benefit
-->Reclamation rewinds 1 to 2 generators each year. Anytime a rotating machine is rewound and the core is replaced,
a risk for electrical design issues resulting in vibration may exist. This risk increases if the winding design is changed
from multi-turn to Roebel bar (single-turn) design. About 30% of conversions have exhibited core vibration issues. It is
desirable to perform these conversions because life expectancy of Roebel bar windings is about 10 years longer than
multi-turn designs constitutes a significant amount of revenue. There are no IEEE or other standards that provide a
reasonable "acceptable level" of core vibration for a rewound unit. Existing standards that deal with vibration are
basically inadequate to protect the customer when a rewind is procured. Research of specific solutions to these
general vibration problems would benefit all regions as most already have units with vibration issues. Mitigating or
significantly reducing stator core vibration issues will extend the life of these units and protect future investment if
problems occur. Knowledge gained will help Reclamation, and the power industry, avoid these issues and correct
-->Currently core vibration issues typically cannot be fixed unless the unit is replaced/redesigned. The ability to
produce field-executable repair solutions for core vibration issues protects existing investments by decreasing O&M
costs and realizing the full expected service life from these machines. There are large costs associated with lost
revenue and labor to perform repair. This research aims to avoid these costs.
-->The research will provide information to update Reclamation's rewind specifications to screen and avoid
encountering these problems in the future. This is estimated to save a myriad of costs associated with analyzing and
diagnosing each case individually on top of increased future O&M costs.
-->It is assumed that Grand Coulee G9 and spare winding, Shasta G1 – G5, Hoover A5 & N7, and Yellowtail G1 – G4
will each take two outages over the lifetime of the units related to addressing vibration issues. If each outage lasts
two-weeks, the estimated cost associated with lost revenue, labor, and parts is approximately $40M.
-->In the case of Grand Coulee G9, two windings of the same less-than-adequate design were procured. One was
installed in G9 and the other is currently warehoused awaiting installation in the next unit that fails. Because there is
resistance to utilize this poorly designed spare winding, the project is considering replacing the winding in G9 unit and
not installing the spare. The ability to successfully modify the existing winding makes both existing and spare windings
viable and is estimated to save about $15M vs. replacing the existing and scraping the spare winding.
-->Hoover A5 and N7 exhibits damage caused by vibration. A5 and N7 were repaired in 2000 after a myriad of
studies. Both units were inspected between late 2016 and early 2018 and N7 was found to be in need of repair again
to avoid catastrophic failure (rotor-stator contact). N7 was found to have recurring problems It would cost an estimated
$1.2M to perform necessary repairs to N7 in 2018, including lost revenue during an outage, labor, and non-labor.
-->Reclamation has existing units with vibration problems which are degrading with every hour of operation. If these
issues are solved early in the life of these machines O&M costs associated with vibration damage repairs can be
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