Why so many transformers are using cores of amorphous instead of silicon steel? Because amorphous has higher permeability than silicon steel and much lower coercive force and remanence, although the material cost is higher.
Amorphous VS Silicon Steel
As a new kind of soft magnetic material, amorphous is becoming more and more popular in recent years. The typical model of iron-based amorphous is 1K101 (Fe78Si8B13, percentage of atoms), which has the highest saturation B value among all amorphous alloy materials commonly used. It has much higher permeability than silicon steel and much lower coercive force and remanence. It can be used as composite cores for DC immune current transformers and so on.
We can see the comparison between iron-based amorphous and laminated silicon steel as the below table.
| Items | Iron-based amorphous 1K101 | Cold-rolled silicon steel |
|---|---|---|
| Saturation magnetic induction (T) | 1.56 | 2.03 |
| Coercive force (A/m) | <4 | <30 |
| Max. permeability | 45×104 | 4×104 |
| Iron core loss (W/kg) | <0.2 (50Hz, 1.3T) | <1.2 (50Hz, 1.7T) |
| Excitation power (VA/kg) | <0.5 (50Hz, 1.3T) | <0.83 (50Hz, 1.7T) |
| Lamination factor | >80% | 95% |
| Magnetostriction | 27×10-6 | / |
| Resistivity (μΩ•cm) | 130 | 0.45 |
| Density (g/cm3) | 7.18 | 7.65 |
| Curie Temperature (°C) | 415 | 746 |
| Crystallization temperature (°C) | 550 | / |
| Hardness HV | 900 | 181 |
| Thickness (mm) | 0.018~0.035 | 0.3 |
Here we can see, choosing iron-based amorphous cores, instead of laminated silicon steel cores for middle & low frequency (50Hz~20kHz) transformers and inductors, we can get the benefit as below.
- High saturation magnetic induction: increase the cores’ working induction and make the cores size smaller.
- High permeability and low coercive force: decrease excitation current of primary windings.
- Low magnetic loss: temperature increase slowly.
The iron loss of amorphous is only a fraction of 1/5~1/3 to that of silicon steel, and permeability is much higher. Therefore, the distribution transformers with amorphous cores inside will have a 75% lower no-load loss than that with silicon steel cores inside. Including split amorphous cores, more and more amorphous 1k101 materials are consumed in the area of power electronics.