Interesting inductor observation - follow up

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

Hello list members 

I am intrigued by the replies that have come to me both personally and through
the Tesla list. Perhaps I should have made the following point clear when I
made the original post: 

The statement about the different behaviour of various inductive ballasts was
only posted as an observation - not as a universal truth. I am quite happy to
accept that in a given circuit, two similar inductive ballasts will give a
similar current-limiting result. 

However, it has been observed (by an experienced transformer manufacturer) that
this equivalence is not always true - that for some circuits, ballasts with
equivalent measured inductances can have different current limiting effects.
There are obviously a large of possible reasons why this discrepancy may occur,
including (but not limited to) errors in the measuring equipment, the
non-linear charging current in a classical TC, and the 'fact' that real
inductors are almost always inherently 'non-ideal' (i.e. end effects, eddy
currents, core hysteresis etc). 

I do not claim an exact knowledge of why some inductive ballasts seem to behave
differently from others, neither do I propose a pseudo-scientific explanation
to account for it. Rather, I am merely reporting it as an observation - as is
often the case with TCs, "your mileage may vary". 

Best-regards and safe-coiling, 

Gavin Hubbard 



> 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. 
> 
> Safe coiling, 
> 
> Gavin Hubbard 
> 
> 
>