Determine transformer weight at 4 corners for sizing spring isolators

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dowen

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Can anyone help with a formula to determine weight distribution of a transformer mounted on 4-spring isolators. The attached shows the center of gravity of a 112.5 KVA. I can use the percentage of one of the measurements to the center of gravity and apply that to the total weight giving something like a 36% 64% split, but I am not comfortable that is accurate.
 

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The picture shows a side view of the transformer. I will call the left side of the photo the front of the transformer. You can calculate the weight distribution (front to back) using this. Your moment arm method is correct: front = 249/688 * 1025#, rear = (688-249)/688 * 1025# However, this does not give you the left-right weight split because you need that center of gravity, too. If it is in the center, then the split is 50/50.
 
dowen said:
... I can use the percentage of one of the measurements to the center of gravity and apply that to the total weight giving something like a 36% 64% split, but I am not comfortable that is accurate.
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Slow poster - As bean says: You got it. 36% on the front and 64% on the back.

It is a sumation of moments problem. Looks like this: View attachment Moments.pdf

ice
 
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I'd think the manuf could help you with that. They should know all the forces at each support point and from there a spring constant, source of supply, etc...
 
If you want to size the support system exactly at the point to which it will fail + 10 or 20% you can use the classic statics formulas ie. sum of the moments = 0 etc. etc. but in reality you or whomever will end up installing it like all the other suspended transformers because it would be more expensive to do it any other way. Almost every transformer I see is suspended with (4) 1/2" threaded rods sitting on a unistrut. I would have to look but I have a detail if you need it?
 
Spring Isolators

Spring Isolators

You are probably safe assuming 25% of the weight on each isolator. When I look at spring isolators, they are all adjustable and have a range of allowable weight. With a 1025# transformer, four isolators rated 230-310# (5XR56 Grainger, Inc.) would seem to fit the bill.

I would worry if the center of gravity of whatever is being hung was way off center but for a transformer, that is unlikely.

Isolators are often required where the owner/builder/engineer is concerned about vibration/hum from the transformer. By isolating the transformer and using flex cable/conduit, the little bit of hum is not transferred to the structure to rattle and annoy the tenants.
 
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