Special Transformers for Industrial Applications

A number of industry applications require specific industrial transformers due to the usage of power (current) as a major resource for production. Electric arc furnaces (EAF), ladle furnaces (LF) and high-current rectifiers need a specific design to supply the necessary power at a low voltage level. These transformer types, as well as transformers with direct connection to a rectifier are called special-purpose or industrial transformers, whose design is tailor-made for high-current solutions for industry applications. 4-1 Electric arc furnace transformers EAF and LF transformers are required for many different furnace processes and applications. They are built for steel furnaces, ladle furnaces and ferroalloy furnaces, and are similar to short or submerged arc furnace transformers (fig. 5.6-1). EAF transformers operate under very severe conditions with regard to frequent overcurrents and overvoltages generated by short-circuit in the furnace and the operation of the HV circuitbreaker. The loading is cyclic. For long-arc steel furnace operation, additional series reactance is normally required to stabilize the arc and optimize the operation of the furnace application process. Specific items EAF transformers are rigidly designed to withstand repeated short-circuit conditions and high thermal stress, and to be protected against operational overvoltages resulting from the arc processes. The EAF reactors are built as 3-phase type with an iron core, with or without magnetic return circuits. Design options Direct or indirect regulation On-load or no-load tap changer (OLTC/NLTC) Built-in reactor for long arc stability Secondary bushing arrangements and designs Air or water-cooled Internal secondary phase closure (internal delta).