Re: Ok, what is an LTR cap.

["Barton B. Anderson" <tesla123-at-pacbell-dot-net> (by way of Terry Fritz <twftesla-at-uswest-dot-net>)]

Hi Ed, 

Tesla list wrote: 
>
> Original poster: Esondrmn-at-aol-dot-com 
>
> In a message dated 8/24/00 7:24:40 PM Pacific Daylight Time, tesla-at-pupman-dot-com
>
> writes: 
>
> << Original poster: "Mark Broker" <broker-at-uwplatt.edu> 
>  > 
>  > > Actually, PIG's are STR's (smaller than resonant). Typically, coilers 
> use a 
>  > 
>  > > 10kva, 14.4kv pig's. Resonant caps are 0.128uF (from memory). Obvisouly 
>  > HUGE! 
>  > > We typically use smaller than resonant caps (STR's) on our systems. 
> NST's 
>  > > however (and OBIT's), can use LTR's. Could you imagine the joules for a 
> pig 
>  > 
>  > > using an LTR? I see smoke, fire, wooosh!!! Well, for most of us, not 
> Greg, 
>  > > Bill, Hull, etc... or you Chris (yet?). 
>  > 
>  > Actually, Terry's MMC Calc gives me .351uF. 
>
>  For a 240/14.4kv, 694mA, 20,749 ohm pig? Terry is .351uF correct? I though a
>
>  matching reosnant cap size should be 0.128uF. Maybe my math is wrong here. 
>  Someone please clarify? 
>   >> 
> As I found out the hard way, you can also get into a 60 hz resonant condition
>
> with probabaly any cap by varying the inductance in the primary used as 
> ballast.  I am using .05uf with a 14.4  5 kva distribution transformer and it
>
> was resonant with the particular welder that I was using.  It was an 
> uncontrollable condition.  Maybe with a sync rotary gap, but not with my non 
> sync rotary. 
>
> Ed Sonderman




Yes, I remember the situation. Your transformer is resonant at .064uF, so you
are close to begin with. As I remember, you went to a 40A variac (uncut) and
that solved the problem. I still wonder why the welder resonated the way it
did? With the variac, you are still ballasting for V and I in-phase at longest
arc length. I guess even though this condition occurs, probably with every
coil, the welder must have had an internal winding capacitance capable of
causing the change in capacitance to cause the resonate condition. I dont'
know, I never measured the capacitance of a welder and applied it's effect on
the circuit. Still, it's an interesting condition that wasn't easy to solve. 

Bart