Re: Interesting inductor observation

["Malcolm Watts" <M.J.Watts-at-massey.ac.nz> (by way of Terry Fritz <twftesla-at-uswest-dot-net>)]

Hi Gavin,
          Very interesting post:

On 20 Jul 00, at 20:51, Tesla list wrote:

> Original poster: ghub005-at-xtra.co.nz 
> 
> 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.

My first question is what differences are there in the cores? 
Are we talking about gapped vs ungapped? Then there is core 
shape. E-I, CC etc.? Core material also figures.?  Then there 
is effective core area and mean length to add as well. ?

    You say "nearly" the same impedance. If the impedance is 
primarily inductive (like a high L), differences in resistance 
will affect the Q somewhat which will affect the resonant 
behaviour if the choke is coupled with a cap as invariably 
happens in a TC charging circuit. I can believe what he says 
but in order to explain the differences answers to these 
questions are needed.

Regards,
Malcolm