Furnace transformer cooling is not a matter of choosing a method and moving on. The cooling method determines how much power the unit can deliver in a given frame size, and on a cyclic load it determines whether the unit survives meltdown.
Where the heat comes from
Three sources matter, and they do not behave the same way over a heat.
- Copper loss in the windings, which scales with the square of the current and therefore tracks the load closely.
- Core loss, present whenever the unit is energised, roughly constant across the cycle.
- Stray and harmonic losses, which become significant on furnace duty because the arc load is rich in harmonics and the secondary currents are large.
The practical consequence is that losses peak hard during meltdown and drop sharply during refining and holding. Cooling sized against an average figure will run short at the point that matters.
Cooling methods
- AN, air natural. Convection only. Limited to smaller furnace units.
- AF, air forced. Fans move air across the cooling surfaces, raising capacity without the complexity of oil circulation equipment.
- OFAF, forced oil with forced air. Oil pumps circulate the oil through external coolers, and fans force air across the coolers. The standard approach for large furnace transformers.
- OFWF, forced oil with water cooling. Used where the heat load exceeds what air can remove. Heat is transferred through a water-to-oil heat exchanger; oil and water are not mixed.
Why cooling method matters more here than on a distribution transformer
On a steady load, cooling capacity can be sized with margin and forgotten. On furnace duty the load is cyclic and the peak is where the risk sits, so the cooling has to be evaluated against meltdown rather than against a nameplate rating.
Forced circulation also has a second benefit on furnace units: it evens out the temperature distribution across the windings, which reduces the thermal stress that cyclic loading imposes on insulation.
Redundancy
A furnace transformer cooler failure during a heat is not a minor event. On large units it is worth specifying two coolers, each individually rated for the full losses, so that the furnace can continue through a single failure. The second cooler costs far less than the lost production from one interrupted campaign, let alone the damage from an over-temperature trip.
What to state in the specification
- Cooling medium available on site: air, water, or both.
- Ambient temperature and, for water cooling, the inlet water temperature and quality.
- Expected cyclic load profile, so cooling can be sized against the peak.
- Whether redundant coolers are required, and the acceptable operating condition after a single cooler failure.
- Monitoring and protection: winding temperature indication and trip settings.
Send the load profile and the cooling medium available, and we can come back on the cooling arrangement and the frame size it supports. See the furnace transformer range, or contact us.
Related Products
Related Applications
- Transformers for Steel Industry
- Transformers for Electric Furnaces
- Transformers for Industrial Equipment
Request a Custom Quote
Need a custom transformer for your application? Send us your technical requirements and our engineering team will provide a custom solution within 24-48 hours.
Where this fits in a wider installation
Transformers rarely sit on their own. In most projects this equipment ends up inside a package that also carries the medium-voltage switching and the low-voltage distribution. That arrangement is described on our industrial power distribution, MV switchgear and transformer substation packages pages.
Frequently Asked Questions
What matters most with furnace transformer cooling?
It is the specification, not the equipment. Most of what goes wrong later traces back to a voltage, fault level or site condition that was assumed rather than confirmed. The questions below cover what comes up most often.
What makes a furnace transformer different from a distribution transformer?
The duty cycle and the load. Furnace duty brings repeated short-circuit and inrush events, very high secondary currents and frequent tapping under load. Windings, mechanical bracing and tap changer selection are all driven by that duty rather than by steady-state load alone.
How is the secondary current handled at these levels?
By designing the secondary for the current it actually carries, with the busbar or cable terminal arrangement settled at drawing stage. Conductor cross-section, support spacing and cooling are decided together, since the mechanical forces at high current are as significant as the thermal ones.
Which standard applies, and is it certified?
The applicable standard and clause set are agreed against your project specification before production starts. Where a project names IEC 60076 for the transformer, we work to those clauses and the routine test report ships with the unit.
What do you need from us to quote?
The single-line diagram or a description of the application, the voltages, the load with its duty, the site conditions, and any standard the project specifies. Send what you have – if something is missing, it can be worked out together rather than delaying the enquiry.