Selecting Between Nanocrystalline and Silicon Steel Cores for CT Designs

Nanocrystalline alloys offer initial permeability in the tens of thousands, far above silicon steel. For metering CT cores working at low flux density, that means fewer secondary turns and lower ratio error, which is why class 0.2S designs usually favour nanocrystalline.

Silicon steel has a higher saturation flux density, around 1.7 to 2.0 T compared with roughly 1.2 T for nanocrystalline. Protection cores that must carry large fault currents without saturating are therefore often built on silicon steel, or on a nanocrystalline core sized with a generous cross section.

Core loss behaviour differs too. Nanocrystalline shows lower loss at power frequency for a given flux density, while silicon steel remains economical at higher flux levels and in large window constructions where material cost dominates.

Temperature stability is another practical factor. Nanocrystalline keeps inductance stable across a wide range, which matters for outdoor meters and inverter mounted sensors. Silicon steel is more tolerant of mechanical stress during assembly.

In short: metering accuracy first, choose nanocrystalline. High current duty and cost per unit first, choose silicon steel. Many customers use both in the same product family, and we can quote a matched pair of designs from one drawing package.