If you’ve got high voltage and need high current – we have the solution.
Furnace Transformers
Introduction
Electric Arc Furnace (EAF) transformers supply the power needed for steel production and special ferroalloys. These applications demand very high power levels and operate under severe conditions, including frequent overcurrents and overvoltages caused by short circuits in the furnace and the operation of HV circuit breakers.
To meet these requirements, many installations use three single-phase furnace transformers rather than a single three-phase unit. Transformers in such service must withstand extreme thermal, mechanical, and electrical stress. The EAF transformer built as a shell-type design is a well-proven technology, recognized for its strength and reliability over decades.
An EAF transformer requires exceptionally high secondary current (often 10 kA or more) with adjustable current and voltage. A shell-type or core-type transformer equipped with an on-load or off-load tap changer on the primary winding allows operators to optimize furnace performance.
For compact and cost-efficient installations, a series reactor can be integrated into the same tank as the EAF transformer. The reactor itself may also be equipped with a tap changer to fine-tune operating values.
Shell-type or Core-type?
There are two fundamental construction principles for furnace transformers, based on the configuration of the magnetic core and windings:
Shell-type (Fig. 2a):
Features a rectangular core cross-section with windings of matching shape. High-voltage (HV) and low-voltage (LV) discs are interleaved with insulating shields. Selected HV discs are tapped for voltage regulation. The LV coils are made of solid copper plates and divided into parallel groups that match the bus-bar system feeding the furnace.Core-type (Fig. 2b):
Built with two legs of roughly circular cross-section. HV and LV windings are mounted concentrically on the core legs, typically with the LV winding placed outside the HV winding. LV windings consist of multiple disc coils connected in parallel to bars leading to the LV bushings.
Advantages and Disadvantages
Both construction concepts can be adapted to furnace applications, but they differ in electrical characteristics:
Shell-type advantages:
Low reactance (2–3 %), typically two to three times lower than a comparable core-type transformer.
Greater flexibility in voltage steps and more uniform voltage distribution.
High mechanical strength of the active part, ideal for heavy-duty furnace service.
Core-type characteristics:
Higher reactance (commonly 4–9 %).
Simpler concentric winding layout, which can suit certain installation constraints.
Because furnace operations generally require low reactance, shell-type transformers are usually preferred.
Contact Us
Looking for a furnace transformer?
Contact us and tell us how we can help meet your power and performance requirements.