Circular vs Square Power Transformer 2

[tefaber]

I posted this question in the motor forum, but may be more appropriate here...

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?

 

[IRstuff]

crossposted from thread237-135119

TTFN

 

[cuky2000]

I showed several decommissioned large circular design power transformer manufacturer by Asea (before the merge with BBC). The maintenance personnel interviewed where not to happy with those transformers because they were prone to leak oil.

I guess the transformer core and winding are similar for both designs. However, they may be some advantage from the natural cooling point of view and possible fewer losses in the tanks do to better symmetry on the distribution of the magnetic field inside the circular vessel.

Since the vast majority of transformer are rectangular design, this make me suspect that there is cost advantage for the manufacturer to choose this configuration.

 

[rcw retired EE]

Here's what I was taught:

Circular windings have more inherent strength against short circuit forces. A square winding can bend in the middle of one (or all) sides during a short circuit and needs additional bracing. A loop or circular winding distributes the mechanical forces around the loop and supports itself. (This only applies to radial forces. Vertical forces are the same for square or circular shapes.)

But a well-braced square winding is better than a poorly braced circular winding. An adequately braced square winding is as good as any circular winding.

The square shape may allow better use of space inside the tank = lower costs.

The true test of a winding shape and bracing is a full short circuit test with measurement of transformer impedance before and after. Movement of winding components during the test shows up as a change in impedance. If there is only minimal change in impedance, the winding design is considered adequate. (A full short circuit test is usually only done as a design verification or type test.)