Self Lm of transformer

[Abdelwakil]

Hi.
What is the range of self induction (magnetizing) of ferrite trans, specially the smps one ? Is it greater than the steel trans ?

 

[marconi]

Ridley Engineering | - Transformer Measurements - http://www.ridleyengineering.com/hardware/ap310-analyzer/ap300-application/transformer-measurements.html

If by self-induction you mean Lm, you need to measure the frequency response of the transformer to estimate/measure the magnetising inductance (Lm). The article above shows you how. Measuring Lm at a single frequency is no good because a SMPS uses pulse waveforms with a wide frequency band (sinx over x shaped). You need to measure Lm over the band of frequencies at which the the SMPS transformer operates.

If by 'range' you mean frequency range then steel laminated cores are used in power transformers operating at low frequencies 1-100 to 1000Hz say - I don't know the exact upper figure -whereas ferrite is used at high frequencies 1-100kHz because its hysteresis and eddy current losses are much less than steel cored transformers. Hysteresis loss is related to the areas inside the BH curve times frequency. Steel is a soft magnetic material (easily magnetised but not easily saturated) and has a 'fat' hysteresis curve whereas ferrite, a hard magnetic material, has a 'thin' curve' see attachment (hard to magnetise but easily saturated). A thin BH curve is required for energy efficient operation at high frequencies hence the use of ferrite transformers in SMPS applications.

Research Center for Magnetic and Spintronic Materials - https://www.nims.go.jp/mmu/tutorials/soft&hard.html

In a transformer the eddy current loss is proportional to frequencysquared - ferrite cored transformers have higher resistivity than steel ones which reduced the magnitude of the eddy currents and hence Ohmic losses (IsquaredR).

This is about as much as I can remember from my degree but hopefully will give you some pointers on further reading.
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https://www.eeweb.com/tools/coil-inductance?utm_source=AspenCore&utm_medium=ELECTRONICS TUTORIALS

Permeability (electromagnetism) - Wikipedia - https://en.wikipedia.org/wiki/Permeability_(electromagnetism)

The loop inductance is:

Lloop≈μoμr(D/2)⋅[ln(8⋅D/d)−2]

The permeability (uour) of steel is higher than that of ferrites (see table in second reference) so the loop self inductance of similar sized single turns (same diameter d of wire, same diameter D of loop) is higher for steel than ferrites.