Furnace Series Industrial Furnace Transformer for Metallurgical Smelting

Product Overview

The Furnace Series is built for one job: feeding a melting or smelting furnace with the current profile that furnace actually draws. Instead of a general-purpose distribution unit, this furnace transformer is engineered around the furnace type and the melt cycle — arc furnaces in steelmaking, ladle refining furnaces, submerged arc furnaces for ferroalloy, silicon, calcium carbide and phosphorus, DC arc furnaces, induction furnaces and electro-slag remelting units.

Every unit is a project design rather than a catalogue item. Capacity, impedance, tap range, cooling and terminal arrangement are fixed against the furnace data you supply, which is why two plants ordering the same nominal rating can end up with two different transformers: a ferroalloy furnace running flat out for weeks is not the same duty as an arc furnace that restrikes its arc dozens of times an hour.

The units are oil-immersed and fitted with an on-load tap changer, with the core and winding assembly held by reinforced clamping structures. They are specified by steel mills and ferroalloy smelters, by EPC contractors building new melt shops, and by plants replacing a failed unit or uprating an existing line.

Furnace Types & Process Fit

• Arc furnace steelmaking (EAF) — the electric furnace transformer here is sized around the swings of arc ignition, melt-down and restrike, holding voltage while the electrode current moves across a wide range within seconds.
• Ladle refining (LF) — long holding periods at low power and steady voltage, so the design has to stay stable through hours of refining rather than through short bursts of melting.
• Submerged arc furnaces (SAF) — ferroalloy, silicon, calcium carbide and phosphorus duty runs at sustained high current with deep electrode immersion, so the secondary side is configured for continuous loading rather than a cyclic arc.
• DC arc furnaces — where the furnace runs on direct current, the supply passes through a rectifier transformer before it reaches the electrodes, which changes the harmonic profile, the electrode arrangement and the protection scheme the plant has to handle.
• Induction furnaces — the transformer feeds a medium-frequency power supply, and the load is steadier than an arc, so regulation and impedance are set for the inverter rather than for arc stability.
• Electro-slag remelting — very low secondary voltage at very high current, with the secondary winding and terminals configured for that low-voltage, high-current duty.

Specifications & Parameters

Figure-8 Winding Technology

On arc furnace models the low-voltage side uses an integrated dual winding laid out in a figure-8 configuration. Because the two halves are formed as one assembly, the heavy inter-winding connections that would otherwise carry the secondary current are eliminated — and on a furnace secondary, those connections are where a disproportionate share of stray loss and local heating tends to sit.

A separate regulation winding works alongside the figure-8 assembly. The arrangement keeps ampere-turns balanced across the winding, so the magnetic forces produced by the secondary current cancel more evenly instead of pushing the coils sideways. That balance is what gives the unit its short-circuit withstand: a furnace transformer meets near-short-circuit conditions every time an electrode touches the melt or the arc restrikes, and the winding has to absorb thousands of those events over its service life.

There is a maintenance side to it as well. Fewer inter-winding joints mean fewer places to inspect and fewer connections that can loosen over years of thermal cycling. The construction is specified for arc furnace models where the secondary current and the short-circuit duty justify it; other furnace types are wound to their own load profile.

Voltage Regulation & Grid Connection

• Tap-by-tap control through the heat — an on-load tap changer adjusts the secondary voltage in steps while the furnace is live, so the operator moves from a high melt-down setting to lower refining and tapping settings without shutting the furnace down.
• A range that covers the whole cycle — melt-down, refining and tapping each want a different secondary voltage, and the tap range is set wide enough to cover that spread on your furnace instead of optimising for a single design point.
• Direct connection at transmission voltage — the high-voltage side can be specified for direct connection to a high-voltage grid, for example at 110kV, so the plant does not have to build an intermediate substation. On projects where this is used, the arrangement saves over 30% in infrastructure costs.
• Regulation on the secondary side — where the furnace type calls for it, regulation is applied as step-grade adjustment on the secondary side, which matches the way an arc or submerged arc furnace is actually operated.
• One tank for both functions on arc furnace duty — the main transformer and the series regulating transformer are often built into the same tank, so the regulating winding shares one oil system, one cooling circuit and one foundation with the main unit.

Efficiency & Loss Reduction

Loss performance on an electric furnace transformer is decided by how well the high-current secondary is handled. Counter-parallel conductor arrangements and electromagnetic shielding are used to keep stray losses away from the tank walls and structural steel, where they would turn into heat without doing any melting work.

The gain shows up against older designs. On a 31.5MVA/110kV model, load loss is 13% lower, no-load loss 17% lower and no-load current 26% lower than the legacy designs it replaces. Load loss is the figure that tracks the furnace current during a heat; no-load loss and no-load current matter between heats and through the long holding periods a refining furnace runs.

For your own rating, ask for the loss figures together with the efficiency at the load points your furnace actually works at — 25%, 50%, 75% and 100% — and for the measurement method and tolerance behind them. A furnace rarely sits at nameplate load, so a figure quoted at one point can hide a different picture at another.

Operating Economy & Safety

• Low-voltage switching instead of HV breakers — a tertiary winding lets the furnace be switched on the low-voltage side, where long-life low-voltage breakers do the work. Those breakers cost less to buy and less to replace than the high-voltage gear that would otherwise be needed.
• Fewer operations on the plant's HV switchgear — moving switching to the tertiary side keeps the most expensive switchgear in the substation out of the daily furnace cycle, which matters on a furnace that is switched many times a day.
• Fault clearing close to the load — switching and protection on the tertiary side keep the interruption near the furnace, so a trip disturbs less of the surrounding supply.
• Constant flux density operation — the core is designed to work at constant flux density, so the active material is matched to the real operating condition rather than over-built around a worst case.
• Power factor correction readiness — capacitor banks for power factor correction can be connected where the plant needs them, without adding a separate transformer for the purpose.

Construction & Design Validation

Furnace duty is not steady duty. A unit in a melt shop absorbs arc flicker, repeated electrode short circuits, thermal cycling between heats and the mechanical vibration that comes with all of it. The core and winding assembly is held by reinforced clamping structures, so the winding block stays where it was built while magnetic forces push against it, heat expands it and the furnace keeps cycling.

Before a design is released it is validated for the three stresses that decide service life: the electrical stresses in the insulation system, the thermal behaviour at the duty cycle the furnace will actually run, and the short-circuit forces generated during a fault or an electrode strike. That work is what keeps a unit in service in a workshop where dust, heat and continuous load are normal.

One practical point to settle at design stage: the low-voltage terminals have to meet the short-net connection to the electrodes. Give our engineers the busbar arrangement and the electrode layout, and the terminal position, phase spacing and clearances are built to match rather than adapted on site.

Testing, Standards & Documentation

Ordering, Delivery & Site Support

1. Start with the furnace: tell us the furnace type, the material being melted, the secondary voltage levels your furnace team works to, and whether the control strategy is constant power or constant current. Whether the process runs on AC or DC matters here, because a DC arc furnace is fed from a rectifier transformer and the duty data is different.
2. Fix capacity and overload: rated capacity and the overload window — continuous or short-time — are agreed against your melt cycle and tap-to-tap time, with the capacity verification basis written into the technical agreement rather than assumed.
3. Confirm the electrical environment: nominal frequency and the deviation your grid allows, phase configuration and whether the load is balanced, the high-voltage connection available at site, and the insulation level and partial-discharge conditions your market requires.
4. Approve the design: drawings, loss data and the tap range are issued for your review before the tank is built.
5. Arrange testing and inspection: routine tests run on every unit — tell us early if you or a nominated inspector want to witness the factory tests so it can be scheduled into the build programme, and confirm which special tests your specification calls for.
6. Packing and shipment: the core and windings are held by six-side rigid locating inside the tank, the unit is shipped filled with processed oil under a nitrogen blanket, and detachable coolers, conservators and control cabinets travel in their own crates. The main tank sits on a heavy-duty steel skid built for rolling, lifting and sea freight.
7. Installation and commissioning: documentation and engineering support cover installation, commissioning and integration with your furnace control system. Check the tank, bushings and crates against the packing list before unloading, and keep the unit as advised until the foundation and the short-net connection are ready.
8. Warranty and after-sales: units carry a 12-month warranty from the date of commissioning or 18 months from shipment, whichever comes first, covering defects in materials and workmanship, with extended support available for critical components such as the OLTC. Lead time, payment terms and shipping arrangements are confirmed with your sales contact for the project.

Capacity & Supply Conditions

Spares & Maintenance Planning

• On-load tap changer parts — the tap changer is the most mechanically active item on the unit and the component covered by extended support, so diverter contacts, drive parts and its gaskets are the first items we recommend holding locally.
• Bushings and sealing components — HV and LV bushings, gaskets, seals and valve packing. They are low-cost, but a damaged bushing or a weeping seal can hold a furnace down while a replacement is in transit.
• Insulating oil and oil-handling consumables — keep processed oil of the same specification used at filling, together with the filter elements and consumables your oil treatment set needs. Units ship filled with processed oil under a nitrogen blanket.
• Cooling system parts — fan motors, pumps, radiator accessories, valves and seals for ONAN, ONAF or OFAF units. Cooling is what limits output on a heavily loaded furnace transformer, so a failed fan or pump is a rating problem as much as a maintenance task.
• Temperature and protection devices — temperature gauges, sensors and gas relay accessories. Small in value, but their failure takes the unit out of service.
• Routine oil testing — sample and test the oil at the interval agreed for your unit. It is the earliest low-cost indication of moisture, oil ageing or a developing internal problem.
• Tap changer inspection — inspect the diverter switch and drive mechanism on the schedule set for your duty cycle. A tap changer that will not step stops the furnace even when the transformer itself is healthy.
• Building your spares list — send the rating, cooling mode and duty cycle, and our engineers confirm which items we recommend you hold locally for your model.

Technical Support & Model Matching

Every project starts with our engineering team. Share your duty conditions, drawings or existing nameplate data, and we help confirm the right rating and configuration before production begins — selection assistance, model matching, and troubleshooting before and after delivery. Backed by more than fifty years in transformer manufacturing, our engineers travel to site for installation and commissioning guidance and stay reachable remotely once the unit is energised. Functions and parameters can be customised to your project, and our quality system holds ISO9001 with IEC, CSA and CTQC testing.

FAQ