Re: OLTC

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

Original poster: "Terry Fritz" <twftesla-at-qwest-dot-net>

Hi Sean,

A good and vital question,  Easy to answer...

http://hot-streamer-dot-com/temp/irg4pf50wd.pdf

The IGBTs have two die in them, the IGBT itself, and one big honk'n ol'
high-teck HEXFRED diode in the reverse direction ("co-pack" since the
TO-247 package contains two devices).  It will take the full IGBT load in
the reverse direction with ease.  Since the coil is basically DC, the big
reverse diode only comes into play during the reverse direction of the
firing ringdown.  I first heard of this idea from Antonio.

IGBTs (and HEXFRED diodes) also have one vital characteristic.  Unlike FETs
that "look like" resistors when on, IGBTS look like diodes when on.  I.e.
they only drop like 5 volts at 200 amps!  So 1000 watts peak loss...  A
good FET with 0.5 ohm loss at 200 amps looses 20,000 watts (100 volts)!
This is the neat thing about IGBTs, they can conduct giant currents with
very low voltage drop and very low loss.

Pole pig systems are "old", OLTC systems are "bleeding edge"...  Lots and
lots of nice pole systems...  Zero OLTC systems...  Of course, there was a
day when that was true of MMCs too, and suddenly oil/poly caps became
extinct...

Exciting isn't it ;-)))

Cheers,

	Terry

BTW - I'll copy the list on this since it is a basic good question that
others must be wondering..


At 11:45 PM 8/17/2002 -0700, you wrote:
>Here's a question for you Terry . . .
>
>I don't know a whole lot about IGBTs, but from what I understand, they're
>basically a BJT, but have an insulated gate (IGbt, duh . . .) like a FET, so
>very little (next to none) current into the gate at DC.  However, (here
>comes the question) aren't IGBTs "one-way" devices?  I.E. Won't they conduct
>current in only one direction?  When the ringdown occurs, current will try
>to flow in both directions of course.  Are the intrinsic diodes taking care
>of this?  What am I missing in the OLTC?  Maybe I should have posted this to
>the list, rather than bother you, and take you away from working on it :-)
>Anyway, hope it goes well, I'm excited to see this thing work, except that I
>was looking forward to get a pig system running, now I don't know if I
>should spend the money on one! :-)
>
>Sean Taylor
>