Power transformer with cubical core

[m.s.j]

A power transformer manufacturer decided to decrease their production budget by reduction of material amount used in transformer construction.
In that country, transformer core material is an expensive portion of power transformer because it shall be supplied by foreign companies. Therefore they began it by saving material used in core construction.
Generally, the power transformer core plates are cut in rectangular form with different sizes (same length, different width) to shape a cylindrical core. In the mentioned company because of traditional product procedure, this method caused a lot of material loss due to plate cutting. Therefore they decided to use cubical shape instead of cylindrical core; they thought the rectangular path surface of magnetic flux is important and circular shape of core cross section couldn't cause any technical benefit. Finally they made power transformers with cubical core with less material because they didn't have any waste cut plates. All electrical tests consist: no load and on load electrical power losses, transformer impedance voltage, percentage of transformer magnetizing current and their harmonic effects were done on new transformers and everything was very well.
However in practice, the new power transformers used in actual power systems couldn't withstand against mechanical stress of sever short circuits.


What is your opinion? How core shape selection influenced the transformer withstand against short circuit current?

 

[dlgoff]

When a power transformer is switched into the circuit, the instantaneous current can cause the coils to move (jump). Could the core shape make it harder for the coils to move and cause damage?

 

[berkeman]

I'm having trouble visualizing the transformer core geometries that you are referring to, m.s.j. Could you possibly post a couple sketches, or post links to pictures/drawings of these transformers?

 

[m.s.j]

I'm having trouble visualizing the transformer core geometries that you are referring to, m.s.j. Could you possibly post a couple sketches, or post links to pictures/drawings of these transformers?

PLEASE FIND ATTACHED

 

[berkeman]

Hm. It looks like you are saying that the old transformer design had a laminated core with a circular cross-section, and the new design uses a laminated square cross-section, presumably with the same cross-sectional area, correct?

If so, then my guess would be that the extra leakage inductance of the square cross-sectional core is causing the problems. The wire windings conform more closely around a round core cross-section, so the leakage inductance of a transformer with a round core cross-section will be lower than with the square cross-section core.

I'm not sure how that translates into the problem that you are seeing under short-circuit load conditions, though.

 

[m.s.j]

In transformers winding it will be seen that anyone coil, either primary or secondary, carries current so that the currents in opposite sides flow in opposite directions, and repulsion forces are thus set up between opposite sides so that the coil tends to expand radially outwards in just the same way as dose a revolving ring or other structure due to centrifugal force. The coil thus tends to assume a circular shape under the influence of short circuit stresses, and therefore it is obvious that a coil which is originally circular is fundamentally the best shape, and is one which is least liable to distortion under fault conditions ( similar to cylindrical or spherical pressurize vessels) .

From this point of view the advantages of the circular core type of construction are obvious.

Why? Why we can not have cubical core and cylindrical coil in a transformer? Are there any electrical reasons?