Static Foundation Design for Eletrical Transformer

[karthikeyans3d]

I am in a need to Design a Foundation for Transformer. Please somebody help me out to find Documents or References to Seismic Design of Static Foundation. A Raft Foundation Design Sample / Example would be Great Help and Highly Appreciated

[gulilero]

Designing a foundation for a transformer should not be any different than the foundation of a heavy machinery which is distributed over a large footprint area but
without the dynamic effects (a transformer will not create dynamic effects). You will still need to consider the lateral load due to seimic effect or wind if this applies to your case.

My suggestion is to create a large enough base-pedestal extending beyond the footprint of your transformer. The pedestal or base should be solid or made with concrete knee walls around the perimeter of the transformer; you may need to include a shallow pool/container below the transformer to contain any potential liquid (oil) spill).
The pedestal for your transformer should extend down to the top of your footing at the foundation level where you have enough soil bearing capacity. The area of foundation should be controlled by the allowable soil bearing pressure. If the seismic lateral force is large enough you need to consider it in the design of your foundation in addition to the vertical loads due to the weight of the equipment and depending if the bearing capacity of the soil has been established based on gross or net stresses you will need to add the weight of the foundation itself. If possible keep the eccentricity (e=M/N) within the base-dimension/6 so that you don't have loss of contact between the base and the soil. Check design for adequate safety factor against: bearing pressure, overturning moment, and sliding (using soil/concre friction coefficient).

[karthikeyans3d]

Dear Er.gulilero Thanks for your Brief Answer.

As you said the Foundation design will be similar in lines with heavy machinery.

But in the foundation which i am design i don't have have have the Lateral Seismic Force directly below the Pedestals of transformer. A percentage of Vertical Load is to be applied at the CG of the Transformer for the Seismic Load. My query is about
1. How to distribute Seismic Load at CG of Transformer to Raft Foundation
2. I would Like to Know is there any ASCE codal provision available regarding the slope of the Pool /Soak Pit below the Transformer and its size calculation.

[avscorreia]

Hi.

Just my two cents on your questions:
1 - Check your local code provisions for the maximum seismic acceleration to consider and multiply it by the equipment mass. You'll get the seismic force that you can distribute easily by the equipment's supports (usually standing on rails, right?;
2 - The volume of the pit beneath the transformer should be able to receive the entire oil volume of the equipment plus a safety margin for additional water that may enter the pit (+10% of the total oil volume, for example). You should check with the equipment supplier for this information.
Regarding the pit slope, I guess that 1% or 2% should be sufficient, but check with the supplier again.

Hope it helped.