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Re: Ballast for pole pigs or potential transformers.




From: 	Adam[SMTP:absmith-at-tiac-dot-net]
Sent: 	Tuesday, November 18, 1997 2:37 PM
To: 	Tesla List
Subject: 	Re: Ballast for pole pigs or potential transformers.


>> * What does an inductive ballast and resistive ballast do?
>
>The ballast is placed in series with the primary of the transformer.
>Because the current reaching the transformer must flow through the ballast
>first, the total current available to the transformer is limited by the
>current used by the ballast device.  For example, if you use a 1500 watt
>electric heater as a ballast, then the maximum power which will flow through
>the transformer is limited to 1500 watts.

Well, the math doesn't work quite like that- the 1500W is what the heater 
dissipates when connected directly to the mains, and is not an intication 
of how much power the transformer is using.  If you have a 1500W heater 
meant for 120VAC service, you want to figure this into your circuit as 
approximately a 10 ohm load.  Unfortunately though, putting this heater 
in series with a transformer changes things a bit.  The heating element 
is really only a 10 ohm load when it is connected across 120VAC by 
itself.  If there is less than 120V across it (e.g. when it is in series 
with a transformer), the element may run cooler and have less resistance 
(resistance of heating elements go up with temperature).

Thus, in order for you to know the exact effect the heater is having on 
your transformer, you have to put the two in series (with the pig's 
secondary hooked to the tesla circuit) and measure the current through 
the two for different applied voltages from 0 to maximum, and make a 
little graph or something.  Measuring the current through and the voltage 
drops across the heater and transformer, you can find out how many VA the 
pig is using.  Volts(rms) times Amps(rms) is known as 'apparent power', 
which is what tesla coiler's usually quote for the rating of their 
systems (in kVA).  For anything other than a purely resistive load, this 
is different from 'true power' in Watts, for which you are being charged 
(True Power = V x I x Power Factor).

>BTW, Richard, pole pigs are not for the inexperienced coiler.  A potential
>transformer or pole pig is not likely to just shock you - it will kill you.
>These are the things that burn the legs and arms off linemen who
>accidentally get across one of them.

Yup, there was a boy a few grades ahead of me in high school who climbed 
up the pole down the street from me, to "get a good view of the city" and 
ZAPPP! It cost him both his arms, and he has since written (um, dictated) 
a book about his experience.  The title was something like "Don't feel 
sorry for me" if I remember correctly.  Definitely fear and respect the 
pole pig, this is one fear that is healthy.

-Adam

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