Re: Considering Upgrading to Pole Transformer

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

Original poster: "by way of Terry Fritz <twftesla-at-qwest-dot-net>" <Tesla729-at-cs-dot-com>

In a message dated 12/15/01 5:57:15 PM Central Standard Time, tesla-at-pupman-dot-com
writes: 

Comments interspersed: 

>
> What are people using for caps with their pig systems? 



"I" am using a commercial High Energy Products brand 
capacitor consisting of 12 identical 27.5 nFD, 42 kVDC 
pulse caps inside one 3" X 5" X 25" long white plastic 
box unit and externally bussed for a 82.5 nFD, 84 kVDC 
unit. I got pretty lucky on this find though. Most people 
still use commercial pulse cap units for big pig coil sys- 
tems, although I think Robin Copini in Australia has suc- 
cessfully used an  MMC in large pig powered system. 
Often the cost of enough MMCs for a pig system outwiegh 
the cost of a single commercial pulse cap unit. Maybe 
since the Geek Group has now got us a bulk discount on 
MMCs, MMCs will start to become more feasible for 
larger high powered systems in the future. 


<?  I know LTR is easier on the NST's --- is  there any 
<need to use an LTR cap with a pole transformer?  And I geuss the answer 
<to that might depend on what type of spark gap I use (synchronous, async 
<rotary, or static). 

I use an asynch rotary gap at ~ 300 to 350 bps, so smaller 
than resonant (STR) is the way to go for me since I doubt 
that the pig could charge the cap(s) fully within the short duty 
cycle. I would recommend LTR caps only for SRSG or TSSG 
systems, whether at NST or pole pig levels. Higher bps, asynch 
systems need smaller caps. 

<Last, current limiting.  I have a variac rated 240 volts, 50 amps, but 
<don't want to modify it in any way - just want it for input voltage 
<control.  I've heard of people using arc welders for inductive ballast - 
<I don't have one.  Can NST's be used?  Could one use one or more 
<depotted 15/60 NST's, (perhaps with secondaries removed?), and add or 
<remove the NST's current limiting shunts to adjust current?   

I use a Lincoln 225 amp Arc Welder with the primary input to the 
welder in series with the pig's 240 volt terminals and short the 
welding leads of the welder. I turn the amperage selector switch 
all the way up (225 amps). This allows the pig to draw 40 to 45 
amps at the full 240 volts input, so that allows me to run up to 
approximately 10 kVA, which is what my pig is rated at. 

<I think I 
<also read that inductive ballast alone doesn't work too well, that there 
<should be a resistive element also.  Any pointers on how this is done, 
<or how necessary it is? 

I too have heard some pig coilers say that purly inductive 
ballast(s) are not suitable but need some resistive ballst 
in combo with the inductance, but I personally use only 
the welder's inductive ballasting for my pole pig and find 
that it works fine. Some people complain that purely in- 
ductive ballastin isn't as smooth as resistive/inductive bal- 
lasting. I don't like the power waste of big power resistors 
in the form of heat, especially in my un- A/C'd shop during 
the hot summer months. And you have to build some sort 
of fire proof housing for the resistors. I guess the inductive 
vs resistive ballasting debate comes down to a matter of 
personal preferance. 

<Are people using PFC caps with pole transformers? 

I don't use any PFCs with my pig and I think most pig 
coilers don't, as pole pigs seem to already have a good 
power factor in Tesla duty. I'll leave any further comments 
on this to the more knowledgable engineers of this list. 

<For my NST setup, I've been using a 240 volt 30 amp house line (electric 
<clothes dryer), stepped down to 120 volt with the variac, to power the 
<NST bank.  Would this be adequate for powering a pig? 

For powering your pole pig, you'll want to stay with the 
240 volts for its input. Most pole pigs have (3) secondary 
terminals (primary for our purposes) and the outermost 
primary low voltage terminals are for 240 volt input with 
the center low voltage terminal a center tap for 120 volts 
to each of the outer terminals (120-0-120 volts). I ran a 
60 amp, 240 volt circuit for my system. A 30 amp circuit 
is a little skimpy for a pole pig but you could make it 
work if you don't push it too hard. A 50 amp range circuit 
would be better. If you only run 120 volts into the pig, you'll 
have to run twice the input current to get the same output 
power that you would with 240 volts input. 

<Thanks, 
 <<  Bill Vanyo 

David Rieben