Normal Magnetisation Curves

Thread Starter

leodavinci90

Joined Oct 22, 2014
57
Hi,
So I am reading about the B-H curve and I came across a term called the "Normal Magnetisation Curve".
It just says that it connects the tips of B-H curves of different materials together. Is that correct? and how does that relate to the Hysteresis Loops of materials?
A link to a tutorial explaining this would also be appreciated!
 

recklessrog

Joined May 23, 2013
985
You asked for a tutorial, below is a quote from this forums own tutorial under the heading "Education" in the forum toolbar. Take a look at transformers under the "A.C" tutorial. Once you have read the tutorial, scan the internet for articles on inductors, transformers, B/h curves, Hysteresis, and a hundred other things that make working with electromagnetism a very fancinating subject. The variables make designing very complex, and without a good understanding of the fundamentals is often the reason that results from a design do not turn out as expected. Real world variations in the materials used can sometimes cause extreme differences between two otherwise apparently identical devices. ( I've been working with them since a very young age, and now at 70, still don't know it all. far from it)

It should be mentioned that the current through an iron-core inductor is not perfectly sinusoidal (sine-wave shaped), due to the nonlinear B/H magnetization curve of iron. In fact, if the inductor is cheaply built, using as little iron as possible, the magnetic flux density might reach high levels (approaching saturation), resulting in a magnetizing current waveform that looks something like Figure below



As flux density approaches saturation, the magnetizing current waveform becomes distorted.


When a ferromagnetic material approaches magnetic flux saturation, disproportionately greater levels of magnetic field force (mmf) are required to deliver equal increases in magnetic field flux (Φ). Because mmf is proportional to current through the magnetizing coil (mmf = NI, where “N” is the number of turns of wire in the coil and “I” is the current through it), the large increases of mmf required to supply the needed increases in flux results in large increases in coil current. Thus, coil current increases dramatically at the peaks in order to maintain a flux waveform that isn’t distorted, accounting for the bell-shaped half-cycles of the current waveform in the above plot.


The situation is further complicated by energy losses within the iron core. The effects of hysteresis and eddy currents conspire to further distort and complicate the current waveform, making it even less sinusoidal and altering its phase to be lagging slightly less than 90o behind the applied voltage waveform. This coil current resulting from the sum total of all magnetic effects in the core (dΦ/dt magnetization plus hysteresis losses, eddy current losses, etc.) is called the exciting current. The distortion of an iron-core inductor’s exciting current may be minimized if it is designed for and operated at very low flux densities. Generally speaking, this requires a core with large cross-sectional area, which tends to make the inductor bulky and expensive. For the sake of simplicity, though, we’ll assume that our example core is far from saturation and free from all losses, resulting in a perfectly sinusoidal exciting current.
 
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