Circular vs Square Power Transformer 3

[tefaber]

I was asked a question about which transformer design is best for a plant using large induction motors (no plug stop)...the largest is two 1250HP motors. The question was whether a circular-design power transformer or traditional rectangular design power transformer is best suited for this industrial application. The transformer in question will step the voltage from 34.5 to 4kv (69kV to 4kV at a later date). I heard that the circular design gives better voltage performance, but the rectangular design is more robust in regards to faults/etc. Has anyone dealt with this question or does anyone know of where I can find information regarding?

 

[Barry1961]

All the circular transformers I have seen have exposed power connections. Don’t know if this would be a problem where they will be.

Barry1961

 

[tefaber]

These are installed in a plant substation separate from the plant, so I think we're okay there.

 

[Laplacian]

Supposedly, the circular or eliptical core transformers are better for captive duty (or large motor duty). We specify this for our captives. The idea is during inrush, the circular or elptical windings are better supported or there is less mechanical stress. I think this came from a manufacturer that builds only circular core transformes though.

 

[dpc]

I think the issue is the shape of the core/coil, not the tank. The manufacturers who make circular coil units will tell you that the this design is much better able to withstand the mechanical forces associated with through-faults (or motor starting) than rectangular core units.

If you get competitive bids on large transformers, my experience has been that the lowest bids will be rectangular core.

From my limited experience, I have never seen or heard of a circular unit failing on a through-fault. I know of a few rectangular units that have failed. But that's not really a statistically significant sample.

 

[ScottyUK]

Thinking about how a coil behaves under fault conditions where the windings are trying to 'burst', the circular coil is already in its fully expanded state, whereas a square winding will have more scope for movement. This lends some credibility to the claims for better fault survivability for this type of transformer.

Most cores aren't true squares, except very small ones, regardless of the shape of the tank. The core has a quasi-circular shape by virtue of the laminations decreasing in width toward the outside of the core structure. The larger the core, the closer the approximation to a circle. The windings are often circular because it is easier to wind them that way - the circular form avoids discontinuities and sharp angles which raise electrical and mechanical stress which then have to be dealt with.


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One day my ship will come in.
But with my luck, I'll be at the airport!

 

[coconutalley]

Contact Dynapower in Vermont. They make the circular type
transformers. They built a 4 MW AC/DC power supply for a customer not too long ago. They claimed the circular was better through more modern design techniques.