The core is where a transformer spends energy doing nothing — its no-load loss runs 24/7 for 30+ years. Two materials dominate the choice: conventional grain-oriented silicon steel (CRGO) and amorphous metal. The right pick depends on loss economics, application and supply, not on one being universally "better."
CRGO is a crystalline silicon steel rolled so its magnetic grains align with the flux — decades of refinement (high-permeability, laser/plasma domain-refined grades) have driven its losses steadily down. Amorphous metal is a glassy iron-boron-silicon ribbon, frozen so fast it has no crystal structure at all, which slashes hysteresis loss.
| Factor | CRGO silicon steel | Amorphous metal |
|---|---|---|
| No-load (core) loss | Low | Very low — typically ~60–70% lower |
| Load (copper) loss | Comparable | Comparable (winding-driven) |
| Core size / weight | Compact | Larger & heavier for same rating |
| Noise | Lower | Higher — needs design attention |
| Saturation flux density | Higher (~1.9 T) | Lower (~1.5 T) |
| Cost / unit | Lower upfront | Higher upfront |
| Manufacturing | Mature, widely tooled | Specialist; brittle ribbon, fewer makers |
Amorphous excels wherever no-load loss is the dominant cost — distribution transformers that sit lightly loaded for most of their life, on grids where energy is expensive or carbon is priced. Over a long service life the energy saved can outweigh the higher purchase price and bigger footprint. It's why several countries with strong efficiency mandates pushed amorphous distribution transformers hard.
CRGO remains the default for power transformers and most heavily-loaded units, where load loss and size matter more, higher flux density keeps the core compact, and lower noise is valuable. It's also the pragmatic choice when capital cost, delivery and a deep, mature supply base are decisive — and modern high-permeability grades have narrowed the loss gap considerably.
There's no single answer — the best core is the one that minimises total owning cost for that specific duty, on that grid, within the size, noise and delivery constraints of the project.
Learn core design in the full course → Read: the lead-time crunch
Educational overview; simplified for clarity. Always confirm material grades and loss guarantees with the manufacturer and the applicable IEC/ANSI standard.