Furnace transformers for AC EAF operation have a large area of applications. From the very demanding and cyclic AC steel furnace operation, with frequent short circuit conditions in the furnace, to the submerged arc operation in ferroalloy and similar furnaces.
These transformers have to be adequately protected against harmonics and frequent overvoltages (HV and LV sides) generated by the operation of the process, and the very high mechanical and thermal stresses have to be contained by a rigid design.
Design Requirements for AC Arc Transformers:
Managing very high secondary currents - for steel up to 90 kA and for ferroalloy up to 160 kA electrode current - and a wide secondary voltage range.
The secondary voltage is normally regulated by means of an on-load tap changer (OLTC), either directly in the HV winding or in an intermediate circuit of a two-core design (booster regulation) within the transformer tank.
Other two-core regulation options are also available, as well as the use of no-load tap changers (NLTC).
For extended arc operation in steel furnaces, an additional series reactor with NLTC or OLTC is optional for improved arc stability. The reactor may be built into the transformer tank or installed separately.
An additional option for steel furnace operation is closing the secondary phases inside the transformer tank.
Technical Data of AC Arc Furnace Transformers:
- Ratings - up to ca. 200 MVA
- Secondary voltages - up to ca. 1500 V
- Reactor ratings - up to ca. 60 MVAr