Transformer Core "Bluish" Discoloration

[ghostbuster7]

2 mva. transformer at 10 % max load recently failed (tertiary delta winding connection opened).

After removing the coils from the core,a partial bluish colour was noticed on the core leg vertical steel plate on each side of this leg.

Question:What could cause this discoloration at such low load levels?

 

[prc]

Was it a dry or oil filled transformer? Did the failed tertiary winding buckled and touched the inside steel plate to cause a current flow through the core ? The blue clour is only on one side ? In all phases or in the phase where tertiary opened out ?

 

[ausphil]

Is the plate in the picture the core steel on its edge, the top layer of core steel, or a separate "steel Plate" of non transformer core steel?

Did you take an oil sample for gas analysis, and if so, did it show overheating?

Also, there seems to be marks underneath the bands around the core. Were these made form the tertiary winding or is it arcing underneath these bands? Are they metallic?

Was there the same discolouration on the horizontal yoke of the core, or was it the same as the rest of the transformer?

Just a guess from what we can see from the photo, it looks like you may have had high circulating current in the steel from what looks like arcing points below the middle band, to the area a bit below the top band.

If you have a shorted turn, or are shorting core steel sheets together, it won't matter too much what the load is, you will be getting high currents.

We'd probably need a bit more info to make a better guess.

Ausphil

 

[ports394]

Typically steel turns blueish color if you set it on fire. So high heat from arcing etc could do that, i think.