Tranformer Bank Busted

[nightfox1925]

Hello folks, there is one situation I got and I am into it as a matter of technical interest. A transformer was operated at Open wye - open delta operation. The bank of 3-333kva transfo was busted. An explossion was heard and it shut down the whole plant. After visually inspected and tested, found out that one of the transfo terminal was lossen. They asked a contractor for repair and rewind and it is going to cost them $4,500. What can you suggest about this situation? For any development. This bank 3-333kva transformer is an aged old installation of this industrial plant.

GO PLACIDLY, AMIDST THE NOISE AND HASTE-Desiderata

 

[LionelHutz]

It would be nice to know what connection failed in the transformer bank and how it was left connected after the failure. We don't know what actually failed.

Having said that, I'm guessing that the bank ended up with only 2 transformers working which changed the bank from being a 1MVA to a 666kVA transformer bank. Then, the operating transformers were overloaded and eventually one failed. If this is the case, a better protection scheme for the individual transformers would be in order.

 

[itsmoked]

Sounds like a regular thermal inspection would've headed this problem off before it got expensive.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[stevenal]

Do I understand that one transformer of a three phase wye delta bank failed, leaving the remaining two to operate open why open delta? Even if the load was 666kVA, this will overload the remaining two.

This is one of the reasons why the primary neutral is generally left floating on these installations. Failure of one unit or primary fuse will cause the voltage to collapse, and load will drop.

 

[burnt2x]

OMG! My take is that those guys thought with 2-333kVA transformers in, you still have 666 kVA cap. With no info posted as to the loading prior to the event, they should have shed load to 577 kVA max(sum of nameplate ratings of equipment loads connected, though 80% loading is safer- 462kVA).
Old taps/ connectors heated-up, transferred heat to the tank, and boom!! Not a good call from the guys at site, I think.