Electric furnace is a broad term. It covers equipment ranging from a small resistance heat treatment unit to an arc furnace melting a hundred tonnes per heat, and the transformers behind them have very little in common beyond the fact that they step voltage down.
The shared electrical job
Every electric furnace transformer does the same thing at the top level: it takes a medium voltage supply and delivers low voltage at high current to the heating element or the electrodes. The furnace converts that current into heat, and the transformer is the interface between the supply network and the process.
Beyond that, the requirements diverge sharply with furnace type.
How the main furnace types differ
- Electric arc furnace (EAF). Melts scrap steel with an arc struck between electrodes and the charge. The load is violently variable, the electrodes short to the scrap repeatedly, and the transformer is built for repeated short circuit duty.
- Ladle furnace (LF). Refines steel after melting, with a more stable arc and a lower power requirement than the main EAF transformer. It still needs arc stability and high current, but not the same short circuit severity.
- Induction furnace. Heats metal by induced current rather than by an arc, so the load is more stable and the electrical requirements are different again.
- Resistance furnace. Heat comes from current through a resistive element. The duty is generally steady, and the transformer behaves closer to a conventional unit.
- Submerged arc furnace. Used for ferroalloys and silicon, where the electrodes are buried in the charge. The load is heavy and continuous, with its own electrode and tapping characteristics.
What the transformer has to be sized against
Because the furnace types differ so much, the transformer cannot be specified from the furnace rating alone. What actually determines the design is the melting cycle: how much material, in how long, at what power, and how often the cycle repeats.
The secondary voltage also has to be adjustable across the heat. Melting a cold charge wants maximum power and the longest arc; refining and holding want less. On-load tap changing lets the transformer move between those states without interrupting the process.
Short circuit duty
Furnace service is not a fault-tolerant duty, it is a fault-rich one. In meltdown, the electrodes make contact with the scrap constantly, and each contact is a short circuit that puts a mechanical force into the windings. The design response is mechanical: braced and banded windings, short and balanced low voltage leads to limit the electromagnetic forces, and verification against the short circuit requirements of the applicable standard.
If a specification for a furnace application does not mention short circuit duty, that is a gap worth raising rather than something to be assumed.
What to send us
- Furnace type and capacity, with the melting cycle.
- Primary voltage and system short circuit level.
- Secondary voltage range and required regulating steps.
- Duty cycle and the expected overload during meltdown.
- Cooling medium available and ambient conditions.
- Applicable standard and any testing requirement.
See the electric furnace transformer range, or contact us with the process information.
Related Products
Related Applications
- Transformers for Steel Industry
- Transformers for Electric Furnaces
- Transformers for Industrial Equipment
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