Mechanical forces or holding down a generator
Mechanical forces or holding down a generator
(OP)
A client of mine is installing an old 1966 2MVA 11kV 50HZ horizontally mounted synch generator. He wants to know what the forces are on the the holding down bolts for civil pad design. Does anyone have any typical information for a generator about this size. Unit is AEI manufacture, almost nothing else known






RE: Mechanical forces or holding down a generator
That torque acts on the feet. If feet are at distance x m, then force will be 13/x kNm or 6/x kNm. There are usually four feet, so divide with two (assuming torque load being taken up equally by the two pairs of feet) to get around 6/x or 3/x kN.
If x = 1 m, then forces will be 6 or 3 kN, or 600 respectively 300 kgf.
That is steady state force. Transient forces, when synchronising and if things like shorts happen on the line, will bring that load up around ten times. So, each bolt shold be able to hold down 6 or 3 metric tonnes of force.
Then, a good safety factor should also be used. A positive thing is that the weight of the generator helps keeping it in place. Still, I would contact a local consultant to get a second opinion.
Gunnar Englund
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: Mechanical forces or holding down a generator
As a reality check, what is the largest bolt that will easily pass through the holes in the mounting feet? Beware of overtorquing the hold down bolts and subtract the preload from the ultimate strength of the bolts.
Bill
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"Why not the best?"
Jimmy Carter
RE: Mechanical forces or holding down a generator
RE: Mechanical forces or holding down a generator
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Mechanical forces or holding down a generator
A change in external load causes an incremental change in bolt load which is given by:
deltaFbolt = deltaFexternal * Kbolt/(Kbolt+Kjoint)
where Kjoint is stiffness of the clamped component.
This relationship applies until joint separation occurs at which time bolt will see 100% of the external load...of course at the bolt load is the external load, still no need to subtract preload.
http://www.boltscience.com/pages/decomp1.htm
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RE: Mechanical forces or holding down a generator
RE: Mechanical forces or holding down a generator
After you have worked out the bolt loads you need to ensure your preload exceeds all the external loads and the method of how you preload your bolts is important, here is a link that gives accuracies of presetting bolt loads as well as theory on bolted joints.
h
desertfox