Why is a motor’s stator a stack of thin, insulated steel sheets? This lesson builds the answer from typical data for 0.35 mm non-oriented electrical steel (M270-35A class): magnetic domains and saturation, the B–H curve and how permeability collapses above the knee near 1.5 T, what saturation does to the magnetic circuit of Lesson 3, the hysteresis loop (Jiles–Atherton model) and why its area is energy per cycle, eddy currents and the classical lamination formula P = π²t²f²B²/6ρ, a fitted loss-separation model, the stator frequency and iron loss of the series’ reference motor, and a bench B–H loop tracer with an RC integrator.
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Chapters
0:00 Thin sheets of steel
0:20 Answers from Lesson 3
0:51 Why iron is easy to magnetise
1:23 The B–H curve of motor steel
2:01 Permeability depends on B
2:32 When the gap stops dominating
3:17 Hysteresis
3:51 The loop’s area is energy
4:36 Eddy currents and laminations
5:25 Separating the losses
6:01 What the stator sees
6:41 Bench: trace a B–H loop
7:25 Predict, then check
Predict before the next lesson
1. Halve the lamination thickness at the same frequency and flux density. What happens to the classical eddy-current loss?
2. Double the frequency at the same peak flux density. By what factors do the hysteresis and eddy-current losses change?
3. The reference motor has 8 poles. What is the electrical frequency in its stator iron at 5000 rpm?
Sources
• Cogent Power Ltd (Surahammars Bruks), Electrical Steel – Non Oriented Fully Processed: M270-35A typical data (peak H vs J at 50 Hz, specific loss 50–2500 Hz, coercivity, resistivity, density) and EN 10106 limits
• Surahammars Bruks, Typical data for SURA M250-35A (2008): used to confirm the 100 Hz / 200 Hz loss tables
• G. Bertotti, General properties of power losses in soft ferromagnetic materials, IEEE Trans. Magn. 24, 621 (1988)
• D. C. Jiles and D. L. Atherton, Theory of ferromagnetic hysteresis, J. Magn. Magn. Mater. 61, 48–60 (1986)
• C. P. Steinmetz, On the law of hysteresis, Trans. AIEE 9 (1892); dates per Encyclopaedia Britannica and the Linda Hall Library; exponent 1.6 as summarised in ABM Proceedings (2014), maximum induction and hysteresis energy in non-oriented steels
• M. Dems, K. Komeza, Z. Gmyrek, J. Szulakowski, The Effect of Sample’s Dimension and Cutting Technology on Magnetization and Specific Iron Losses of FeSi Laminations, Energies 15, 2086 (2022)
Code, captions and transcript (lecture-forge):
Narration is a synthetic voice (Kokoro-82M). Visuals and calculations are generated from code.
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