Re: CD 942 failure tonight

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

Original poster: "Gerry Reynolds" <gerryreynolds-at-earthlink-dot-net> 

Hi Terry (and John),

John using 4 strings of 9   0.15uf caps for a total of 66.7 nf.  My spice
simulation for that value indicated that 26KV could result if the safety
gaps didn't fire.   Given enough RMS current to make the primary hot and
potential for high voltage, I'm wondering if the failure was a combination
of the two.  I think John should increase the number per string and increase
the total capacitance to 83 nf.  Also set the safety gap at the SRSG and at
the NST to just not fire with the unloaded NST voltage.  It might be useful
to verify the Vs_oc and Is_sc values to make sure the NST isn't doing
something unexpected.  If the shunts were altered, or like you say are
saturating, I would think this could have the affect of raising the Cres of
the transformer.

I don't remember if John indicated 50 or 60Hz line.  I've been assuming 60Hz
in the calculations (John, maybe you can verify this).  If he does have
50Hz, then the Cp needs to be raised to 100nf.

Does seem like the Cp needs to be close to the primary and SRSG because of
the high current paths.

Gerry R


 > Original poster: Terry Fritz <teslalist-at-twfpowerelectronics-dot-com>
 >
 > Hi John and All,
 >
 > I looks at John's video and caps:
 >
 > http://hot-streamer-dot-com/temp/P3070026.jpg
 >
 > There is just a big hole in both about 3/16 inch deep.  It looks like it
 > just exploded...  There is not enough energy in a single cap to do that so
 > I don't know where all the energy came from.  There was no other arcing
 > inside.  It just looks like it got a single high energy over voltage that
 > blew a big hole in the cap.  Apparently John does not have the strings
 > cross connected or anything like that.
 >
 > I think he should set his safety gaps like this:
 >
 > http://www.pupman-dot-com/listarchives/2000/January/msg00044.html
 >
 > The resistors were very well attached, far from the cap, and checked out
 > fine.  So I don't see any obvious cause.
 >
 > There is a small chance the big 12/120 NST Transco is saturating the
shunts
 > and maybe putting out too much voltage/current but I have never seen that
 > before with a LTR rotary.
 >
 > One thing that does worry me.  He has his primary far away from the cap,
 > NST and all.  They are hooked up with about 6 feet of wiring.  I wonder if
 > that long primary wire's inductance is doing something odd and causing
high
 > voltages back on the caps or something?  I am not sure if that would do
 > something bad or not.
 >
 > So I don't know what is going on really :-(  but something sure is
 > strange.  He says the primary gets hot and the cap are heating some.  I'll
 > grind the cap through the center tomorrow and see if there is heat damage.
 >
 > Cheers,
 >
 > Terry
 >
 >
 >
 >
 >