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Special Furnace Transformers vs AC and DC Electrical Arc Furnace Transformers

Aug 07, 2020 Source: DanCarbon Writer: Yvonne
Special Furnace Transformers vs AC and DC Electrical Arc Furnace Transformers
Special Furnace Transformers
Furnace load cycles vary widely, depending on size and metallurgical requirements. Many furnaces have load cycles falling within the range of several hours, varying depending on whether the supply is for melting or refining. The melting period is characterised by heavy current fluctuations caused by arc instability and movement of the charge, with less fluctuations occurring during refining.
Utilities supply power at very high voltages which must be converted to low voltages suitable for the furnace arcs. EAF transformers receive the primary low current, high voltage current, high voltage power and transform this to a high current, low voltage power for use in the EAF.
AC and DC Electrical Arc Furnace Transformers
Reliable industrial operations totally depend on the quality and reliability of the EAF transformers, many of which are rated above 100 MVA.  
The AC furnace transformer must be specially designed to withstand frequent short circuits on the secondary side. Currents drawn in the arc furnace are characterised by wide fluctuations and unbalanced conditions, leading to voltage drops, harmonics, etc. These effects can be reduced by supplying furnaces directly from a high capacity, high voltage transmission line through a furnace transformer, while also taking suitable measures to protect the secondary winding from transferred voltages from the HV primary winding. DC furnace transformers have a higher efficiency and the added advantage that there are less disturbances returning into the supply system.

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