Re: [TCML] Re: Tesla Digest, Vol 26, Issue 7

["Dex Dexter" <dexterlabs@xxxxxxxxxxx>]

Constructing a low impedance primary with
a large bang size in the same time presents
a real challenge,doesn't it?
I don't know if you saw it ,but if you didn't
,here is the link where IGBTs are heavily
abused by 4 kw tesla transformer:
  
http://scopeboy.com/tesla/t4spec.html

Not the example of a very efficient coil,but
it works.The point is maybe it's not entirely
impossible you could drive your coil with
only 4 IGBT modules in parallel!

And I am curious too.Can you elaborate bit more
on the output impedance and the secondary circuit
test set-up (Q/A #3)?Sounds intersting but I am
not sure I quite understand.

Dex


--- uhvsystems@xxxxxxxx wrote:

From: uhvsystems@xxxxxxxx
To: tesla@xxxxxxxxxx
Subject: [TCML] Re: Tesla Digest, Vol 26, Issue 7
Date: Sun, 06 Dec 2009 12:11:58 -0500


Steve,

Your reply confirmed my fears.
The same thing about IGBT probable destruction by too high peak currents induced saturation I was told by my colleague Mayer.No need for the test of this sort.It would only unnecessarily destroy one IGBT module.If the limit of 1200 A is given by manufacturer one should respect that and stay within safe margins.Back to the drawing board..You asked some questions and it is my turn to answer.

Q: Why not to parallel these HVIGBT modules?
A:Paralleling 12 of them requires space and increases total parasitic inductance of the primary circuit.That is not a desirable feature having on mind 1 turn primary coil design.Another thing is that it looks we have only 4 of these modules in a stack,and would need ordering 8 more.Not so big problem for us,but anyway..

Q:What is OSIV?
A: OSIV= Oscillatory switching impulse (over)voltage.   Such transients occur as the consequence of HV switchgear (de-)energization activities,faults clearing,distant lightning events etc.GIS monitoring over years clearly shows OSIVs have high the potency of damaging insulation of HV equipment ,triggering restrikes during operative sessions of HV circuit breakers,and causing various sorts of other problems in  power networks.

Q:What is the impedance of the tesla coil concept under consideration?
A:The output impedance is the effective capacitance of tesla coil screening electrode and the tested objects attached to it.In the cases without insulation breakdown the energy gets dissipated in the form of the joule heat in secondary circuits,at decay rates dictated by secondary circuits' Q.

Regards,

Fez Zaev 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~



Steve Ward <steve.ward@xxxxxxxxx>

To:
Tesla Coil Mailing List <tesla@xxxxxxxxxx>

Subject:
Re: [TCML] Re:Pros and cons

Date:
Fri, 4 Dec 2009 19:34:30 -0600



Its obvious now that i did not inspect your proposed design :-)
Yes, 15kA will be too much for those dies (dont bother testing, it will be a
isappointment).  Im not sure how this higher voltage silicon behaves, but i
ound that a CM300 (1200V variety) module begins to de-saturate at about
200A when applying 30Vgs, at which point destruction is immediate.  Aside
rom the sure destruction via de-saturation, the pulse heating will fatigue
he thing eventually.  It should be somewhat easy for you to figure out the
ransient die heating based on a model of the Vce vs Ic.  If the delta T is
ore than 30 Celsius, then its probably not gonna last very long (i admit, i
ave no idea how long that is), but it sounds like 30 degree's is about the
imit that many pulse semiconductor applications like to run up to.
Why not parallel these modules?  It sounds like it would be pretty
uccessful as the di/dt is low at turn on.
But, come to think of it, im confused slightly about your requirements for
nergy.  I dont know what OSIV is, so maybe thats why im confused.  Anyway,
here is the energy going if you are not producing sparks?  More
mportantly, what is the impedance of your load?  I suppose i shouldnt be
uestioning you about this as you surely know more than me about it, but im
till curious.
Steve

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