RE: OLTC update - primary IGBT loss

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Malcolm Watts by way of Terry Fritz <twftesla-at-qwest-dot-net>" <m.j.watts-at-massey.ac.nz>

Hi Gary,
        I'd like to make some comments although this is addressed to 
Terry:

On 3 Sep 2002, at 12:23, Tesla list wrote:

> Original poster: "Lau, Gary by way of Terry Fritz <twftesla-at-qwest-dot-net>"
<Gary.Lau-at-hp-dot-com>
> 
> Hi Terry:
> 
> While primary circuit Q has always been viewed as important, I recall many
> considered opinions suggesting that secondary Q was not so critical.

I think that if I have been guilty of making such statements in the 
past, it was based on the assumption that the de-facto standard 
guidelines for building the coil were being met (e.g. a thousand 
turns or so, h/d 3 - 5, and so on. In the past, I have deliberately 
wound bad secondaries to gauge their effect and always, without 
exception, found them to suffer difficulties ranging from very high 
losses to serious over-volting with moderate amounts of Ep. 
Sometimes, one can get the most bizarre effects from them by driving 
them way off tune (e.g. corona looping from  the top to 1/3 way down 
the winding) but for serious coiling, they were never going to hack 
it.
      Secondary Q *is* important - prior to breaking out at each 
bang, you want the output voltage to go as high as possible and in 
the case of a heavily toploaded coil, it can mean the difference 
between being able to breakout and a bad case of racing arcs. 

> Suggestions were made to wind secondaries with Litz wire, and the
> prevailing response was that secondary losses (in disruptive coils) were
> not worth fretting over.  Please help me to reconcile this with your
> secondary situation.  Is your secondary just outrageously more lossy than a
> typical secondary coil?

IMO, yes. I've seen bad performance from low-L coils and very high-L 
coils. There is definitely a happy medium to be found for a given 
physical coil size.

Regards,
malcolm