# Heavy Industry Process Transformers: Electric Arc Furnace (EAF) & Green Hydrogen Rectifiers

> Electrodynamic short-circuit forces from 100 kA arc furnace currents, cyclic thermal stress, OFWF water cooling, and 24-pulse phase-shifting rectifier bridges for electrolysers.

- **Category:** Special Process Transformers
- **Author:** Voltformer Heavy-Industry Engineering Group
- **Publication Date:** 2026-07-14
- **Reading Time:** 9 min read
- **Key Tags:** #EAF, #Arc Furnace, #Green Hydrogen, #Rectifier Transformer, #OFWF
- **Canonical URL:** https://voltformer.com/articles/eaf-arc-furnace-and-green-hydrogen-rectifier-transformers
- **Markdown Source:** https://voltformer.com/articles/eaf-arc-furnace-and-green-hydrogen-rectifier-transformers.md

### 1. Extreme Process Duty in Steelmaking & Hydrogen Production

Process transformers endure severe mechanical and electrical stresses far exceeding standard distribution equipment:
- **EAF Transformers:** Low secondary voltage ($400 - 1200\text{ V}$) with massive currents up to **$120\text{ kA}$**.
- **Green Hydrogen Electrolysers:** Continuous high-current DC supplies via multi-pulse rectifiers.

### 2. Technical Comparison: EAF vs Hydrogen Electrolyser Transformers

| Parameter | Electric Arc Furnace (EAF) Unit | Green Hydrogen Rectifier Unit (PEM / Alkaline) |
|---|---|---|
| **Secondary Current** | **$60\text{ kA} - 120\text{ kA}$ AC** | $10\text{ kA} - 40\text{ kA}$ DC per bridge |
| **Short-Circuit Frequency** | **10 to 20 dead short-circuits per heat** | Smooth continuous DC load |
| **Cooling Method** | Forced Oil-Water Heat Exchangers (**OFWF**) | Forced Oil-Air (**ONAF / OFAF**) |
| **Pulse Configuration** | Direct furnace electrodes | **24-Pulse ($\pm 7.5^\circ$ phase-shifted)** |

### 3. Electrodynamic Short-Circuit Force Formulation

Electrodynamic radial and axial forces on transformer windings scale with current squared ($I^2$):

$$ F_{radial} = \frac{\mu_0}{2} \cdot \left(\frac{N \cdot I_{sc}}{h_w}\right)^2 \cdot 2\pi R_w $$

To withstand $120\text{ kA}$ short-circuit forces, EAF coils use hardened copper conductors clamped under $10\text{ MPa}$ hydraulic pressure.

### 4. 24-Pulse Harmonic Cancellation in Electrolysers

Electrolyser transformers split secondaries into four phase-shifted systems ($+22.5^\circ, +7.5^\circ, -7.5^\circ, -22.5^\circ$), canceling all harmonic currents up to the 23rd harmonic and achieving **THD-I $< 4.0\%$**.

*Reference: IEEE Std C57.18.10-2021; IEC 61378-1:2011.*

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