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What will happen if transformer core is made of aluminium which is a paramagnetic material?

I know transformer core is made of iron which is a ferromagnetic material. The reason is a small amount of magnetizing current can produce a thousands of times magnetic field inside the core.

This was asked in a interview. Please clarify this.

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  • \$\begingroup\$ You wouldn't have saturation and no hysteresis \$\endgroup\$
    – Voltage Spike
    Jun 10, 2018 at 3:10
  • \$\begingroup\$ So, what will happen then ? Current will continuosly increase and will burn the winding right ?? \$\endgroup\$ Jun 10, 2018 at 3:21
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    \$\begingroup\$ I think the most important thing is that aluminum is a conductor. It will not act as a transformer core, it would more likely act as a shorted secondary winding of an air core transformer. \$\endgroup\$
    – user80875
    Jun 10, 2018 at 3:25
  • \$\begingroup\$ @NikhilKashyap Yes, if your source resistance is zero, your coil resistance is zero and your voltage source is ideal \$\endgroup\$
    – Voltage Spike
    Jun 10, 2018 at 3:40
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    \$\begingroup\$ @NikhilKashyap then your current is limited to the resistance of the coil \$\endgroup\$
    – Voltage Spike
    Jun 10, 2018 at 3:45

4 Answers 4

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There is no significant difference between the magnetic susceptibility of aluminium, and of free space. If that of free space is normalised to 1, transformer iron is in the 2000 to 5000 range, aluminium is 1.000016. So magnetically, the transformer might as well be air-cored.

Aluminium is a good conductor however, better than iron. Even transformer iron has to be formed into insulated laminations, wires or powder to reduce the losses caused by the effective shorted turns that loops of conductor within the core cross-section at right angles to the flux would cause. The same would need to be done with the aluminium core.

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  • \$\begingroup\$ Wiil it behave as a transformer ? \$\endgroup\$ Jun 10, 2018 at 6:58
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    \$\begingroup\$ @NikhilKashyap You've got a clear, verbatim answer to your first question ("will it behave as a transformer") in this answer. You need to read the answers, and understand them. If you can't understand them, ask about what words you specifically don't understand. Your second comment makes even less sense. \$\endgroup\$ Jun 10, 2018 at 11:25
  • \$\begingroup\$ sorry I think due to my weak english I was not able to understand in the first read. I got it now. \$\endgroup\$ Jun 10, 2018 at 14:24
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A solid aluminium core will act as a shorted turn. If made from insulated laminates of the same thicknesses as a regular power transformer's iron laminates, it will still act like a fairly good shorted turn because aluminium has an electrical conductivity that is much smaller than silicon steel.

But there is no point because aluminium brings nothing to the party; it has no beneficial magnetic properties that can magnify the inductance of a winding (important in power applications); in fact it reduces the inductance because of it acting as a fairly conductive shorted turn.

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  • \$\begingroup\$ Does your graph have a source and context? \$\endgroup\$
    – HarryH
    Jun 10, 2018 at 11:46
  • \$\begingroup\$ @HarryH Try this \$\endgroup\$
    – Andy aka
    Jun 10, 2018 at 11:49
  • \$\begingroup\$ Thanks. I was taken aback a bit by your graph which shows Alu-Cu-Fe. Not in the order that I expected, but that's of course because iron has that \$\mu_r\$ in the denominator of \$\delta\$. \$\endgroup\$
    – HarryH
    Jun 10, 2018 at 12:17
  • \$\begingroup\$ I think skin depth is of less relevance here in a traditional transformer region (50 - 440 Hz). The core (iron) losses are due to current loops in cross section of the laminations. So if your lamination is 0.5mm thick the current forms a look with current flowing 0.25mm in one direction and 0.25mm in the other direction. This is smaller that the skin depth and likely not to be affected by that characteristic. Bulk conductivity effects will likely dominate. An interesting thing to research though. \$\endgroup\$
    – KalleMP
    Jun 10, 2018 at 14:15
  • \$\begingroup\$ Yes, it's not about skin depth rather than electric losses due to the eddy currents which increase when the thickness of the iron increases. Indeed, at thicker iron laminations, the area of the loop through which the flux goes is larger, and so the induced voltage and 'short circuit' current. \$\endgroup\$
    – HarryH
    Jun 10, 2018 at 18:16
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What will happen if transformer core is made of aluminium which is a paramagnetic material ?

It will act like an air-core transformer with the characteristic low magnetic coupling between the windings and the very high magnetizing current but it will have a much higher core loss, also compared to the iron core transformer.

It will be quite useless for traditional applications.

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The ideal magnetic circuit should have high permeability and low resistance. This property is present in the magnetic material of Ferro.

Now, coming to the issue above, the aluminum is nowhere near ferromagnetic properties. It's a paramagnetic material, so there's no need of aluminum.

In reality, raw iron is not used, Grain-oriented electrical steels are used. These are iron-silicon alloys that have low core losses and high permeability required for more powerful and economical electrical transformers.

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