A furnace transformer is a transformer built around one unusual condition: the secondary carries a very large current at a very low voltage, and the load swings violently rather than sitting steady.
What separates it from a distribution transformer
Both step voltage down. The difference is the shape of the duty. A distribution transformer supplies a load that changes slowly and rarely exceeds its rating. A furnace transformer feeds an arc or a melt that overloads it hard for part of the cycle, drops to near nothing for the rest, and shorts out repeatedly along the way.
That single difference drives almost everything else in the design.
- Very high secondary current. Melting power is delivered at low voltage and high current, so the secondary winding and its leads have to be built for amperages that would be absurd on a distribution unit.
- Low secondary voltage. The voltage is set by what the arc or the melt can use, not by what is convenient to generate.
- Impedance chosen for arc stability. Furnace transformers run at higher impedance than distribution practice, because higher impedance limits the current when the electrodes touch the charge.
- Mechanical strength against repeated short circuit. The load is a repeated short circuit by nature, and each event puts a mechanical shock into the windings.
- Cooling sized for a cyclic load. The cooling has to handle peak losses during meltdown without being grossly oversized for the rest of the cycle.
Where furnace transformers are used
- Electric arc furnaces for steel melting.
- Ladle furnaces for secondary steel refining.
- Induction furnaces for metal melting and heating.
- Submerged arc furnaces for ferroalloy and silicon production.
- Resistance and heat treatment furnaces.
- Glass melting and other high-temperature industrial processes.
Why the duty cycle decides the rating
The rating of a furnace transformer is not set by the average power. It is set by the thermal duty, which comes from the melting cycle: charge weight, tap to tap time, power on time per heat, heats per day, and how far the furnace is pushed during meltdown.
A furnace driven hard for a short melt and then left idle needs a different design from one run steadily at moderate load, even when the average power works out the same. This is why selection starts from the process rather than from a kVA figure.
Regulation without stopping production
Furnace work has distinct phases, and each wants a different voltage. Meltdown needs maximum power and the longest arc. Refining needs less. Holding needs just enough to keep the bath at temperature. On-load tap changing is what lets the transformer move between those phases without interrupting the heat.
The number of steps matters more than it first appears. Finer steps give better control over arc length and electrode immersion, and that translates directly into electrode consumption and energy per tonne of metal.
What to send us
For a furnace application, the process information is as important as the electrical data.
- Furnace type, capacity in tonnes and the melting cycle.
- Number of heats per day and tap to tap time.
- Primary voltage and the system short circuit level.
- Secondary voltage range and the number of regulating steps required.
- Impedance requirement, or the furnace manufacturer’s recommendation.
- Cooling medium available and the ambient conditions.
- Applicable standard and whether type testing or witness testing is required.
See the furnace transformer and arc furnace transformer ranges, or contact us with the process details.
Related Products
Related Applications
- Transformers for Steel Industry
- Transformers for Electric Furnaces
- Transformers for Industrial Equipment
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