[TCML] Re:Pros and cons

[uhvsystems@xxxxxxxx]

Steve,

Calculated and simulated average currents in considered  tesla coil primary circuit  are well below  max average current rating of the IGBT  (=600 A).
Other dynamical characteristic satisfy as well.However,I'm not sure it is safe to stress the thing repetitively by peak currents higher than 20x rated one.
If you ask IGBT manufacturers or distributers what they think of that idea you'll get an  answer in a style "Run it on your own risk".
Specification of the IGBT module we are talking about you can also see online at:
  
http://www.datasheetarchive.com/datasheet-pdf/019/DSA00326011.html

Notice the guaranteed application only up to 1200 A.
It looks we will have to conduct some 15 kA impulse current tests and see if the IGBT module can withstand that.
Needless to say ,it always remains possibility to put 2 IGBT modules of the same type in series or parallel and lessen some of the design problems,but I dislike that idea becouse of other things.



Dex,

I know what high currents are capable of.Not only electrothermaly but electromechanicaly too.One more reason to pay special attention to design and construction details of tesla coil primary circuit under considerations.
On a side note,it doesn't matter if I like sparks or not.It is simply that the appearance of the spark on HV equipment usually means a bad thing:power arcing.We try to avoid that all the time,except in the places where is 
unavoidable or necessary (ex:ignitrons,contacts of HV circuit breakers etc).


David,

Making or ordering HF oscillator in 500-1000 kW range for our testing purposes is a bad idea.Unexceptable both  application-wise and money- wise.


Regards,

Fez Zaev       

Steve Ward <steve.ward@xxxxxxxxx> wrote:
 
Fez,
It sounds to me like you know what you are doing, to the point that it will
work.  the IGBT you have should be fine for the modulator approach you are
going for because the long turn-off tail is mitigated by turning off the
IGBT switch while the primary current is free-wheeling through the IGBT
anti-parallel diode (giving a huge window for zero-current turn off).  Those
IGBTs would NOT be very suitable for DRSSTC operation, where an H-bridge of
IGBTs must switch at the coils resonant frequency (its basically a big AC
drive to excite the primary system).
155J is an *impressive* energy.  Something on that size would have the
capacity of producing sparks in the 20 foot range (if optimized for spark
production), though i realize that is not your goal.
Steve Ward

Dex Dexter <dexterlabs@xxxxxxxxxxx> wrote :
 
Fez,
20 microfards and 4.4 kV will give bang size of aprox 193 J!
At F ~ 25 kHz you will have primary characteristic impedance
only 0.3 ohms and really high peak primary current ( 13 kA +).
I doubt anybody has ever worked with  tesla coil primary currents
of this magnitude.One thing is certain,your coil will not be a very
efficient one.I doubt it would be able to reach efficiency like 80%.
Pay your attention to this fact.
I hope IGBT HV module you refered to will be useful for the coil.
BTW,interesting standpoint about efficiency issue I must admit.
Reminds me of the view of coiler Peter Teren (aka Tesla downunder),
except in one big difference.He wants and likes sparks,you don't.
Dex 


David Rieben <drieben@xxxxxxxxxxx> wrote:
 
Sounds like you don't want a "Tesla coil" at all then, but instead a 
large, high powered oscillator circuit, like for a multi-kilowatt radio 
transmitter.? 
 
David 

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