About furnace transformers

[tsknan]

Anybody tell me about which transformer Star-Delat or Star-Star is more suitable for supplying power to furnace transformers?
Any specific requirements for power system (Fault level,voltage level etc.)for supplying power to furnace transformers?
recently one power transformer(in a bank of 50MVAX3) connected to furnace tr. of 42 MVA rating failed ,while in service.during the failure the furnace tr. feeder also had fault,the furnace tr. was feeding from 33KV level,delta connected system,with zig-zag gr. transformer in service.
Please help

 

[DanDel]

I suppose you should check with the manufacturer of the furnace transformer for the recommended supply.

 

[slavag]

100% agree with DanDel

 

[tsknan]

one thing i forgot to mention,ours is power transmission system,we are supplying power to the consumers,one of the consumer is having furnace tr.

 

[DanDel]

I think my first post still applies.

 

[prc]

As Dandel said, Furnace manufacturer will normally give guide lines.You can also refer to J&P transformer book ( 12th edition page (Page 739) which give some details.
A major requiremenmt is that this feeding trf to furnace trf should be connected to a strong grid ie with high short circuit level.So in your case for 42 MVA size of furnace transformer, it will be better to use a feeding transformer connected to 220 kV grid.Transformer should have good short circuit current with stand capability.

 

[TurbineGen]

tsknan, consider the nature of the loading of an arc furnace. When they begin a melt, the transformer delievers many high current surges, often exceeding the nameplate rating for a few cycles at a time, then dropping. These surges are also not at all balanced! In every mill I have seen, the operator controls each electrode idividually, and often adjusts the current by the height of the electrode on the fly against a volley of arcs and flying steel and changing conditions inside the furnace. Many of the switchyards I saw had Star-Star connected transformers to supply their furnace transformers. Admittedly, I don't know why.

I would also suggest not only looking into the connections, but also the construction. This might be a time where a shell form transformer is a better option than a core form.

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If it is broken, fix it. If it isn't broken, I'll soon fix that.