Transformers to feed Electric Arc Furnace steel plant

[Elec777]

Dears,
we have 2X20MVA power transformers 66/33 KV WORKING IN PARALLEL TO FEED AN ELECTRIC ARC FURNACE
(WORKING THROUGH INVERTER )AND ITS AUXILURIES&UTILITIES, THE TOTAL LOAD IS 35MVA, WHAT ARE THE RISKS AND POSSIBLE DANGEROUS
INVOLVED IN CASE OF ONE OF THE TWO TRANSFORMERS FAIL, AND WHAT'S THE BEST SCENARIO TO OPERATE THE TRANSFORMERS.
THANK YOU

 

[electricuwe]

At first let me note that I'm surprised about you statement "working through inverter". Usually arc furnace are feed either by a furnace transformer with 3 phases (furnace with 3 electrodes) or via a rectifier transformer and a rectifier (sometimes called converter) with DC (furnace with 2 electrodes).

In both cases the transformer (furnace transformer or rectifier transformer) has to be designed specifically for the stress of this application. If there are upstream transformers only feeding the furnace the will be exposed to comparable stress and should also be specifically designed for this purpose. A standard distribution transformer will rarely be suitable for this purpose.

When designing on white sheet of paper of cause the best solution is to order the furnace or rectifier transformer with a primary voltage directly matching to the available voltage.

What is in you case the reason for stepping down to an intermediate level of 33 kV first ? Maybe you can share some schematics or other more detailed information.

 

[Parchie]

In my early life, we have three small furnaces(electric) and it is not a problem for as long as we follow the "rated" amperage of the units. There are taps on the transformer that supply the electric furnaces such that depending on the requirements of the process, we just "turn down" the current if too much and vice versa! If you put the taps too low, the furnace arc might not melt the shredded metal load/ pig iron at the sides but just burn through, even damaging/ making a hole on fire clay base of the furnace!