Interesting inductor observation

[ghub005-at-xtra.co.nz (by way of Terry Fritz <twftesla-at-uswest-dot-net>)]

Something that might be of interest...

I was talking to a transformer specialist today. 
Although not an EE, he has been designing and 
manufacturing transformers and inductors for the 
last few years. He says that when designing an 
inductor for a current limiting application, it 
is not enough to simply specify the inductance 
and the line voltage for the inductor.

Apparently, different inductors with the same 
inductance (but different physical designs) will 
often behave completely differently when placed 
into a live circuit.

He said that an example is when you tune a TC's 
input current with an variac-inductor, measure 
the inductance of the variac, and build a fixed 
inductor with the same inductance. It seems that 
you will invariably get different performance 
results from the coil when you switch between the 
inductors.

This effect does not apear to be attributable to 
core saturation in the inductors. Also, the 
impedance of the two inductors is measured as 
being (almost) the same.

Does anyone out there know why this effect 
occurs? Presumably it is a magnetic effect - 
possibly to do with the flux density or 
magnetising currents? Or maybe it is just a 
tuning phenomenon that is peculiar to the TC.

I would be interested to know what others think 
about this, or if anyone else has experiences 
this.

Safe coiling,

Gavin Hubbard