Re: pole pig chart (fwd)

---------- Forwarded message ----------
Date: Fri, 24 Apr 1998 10:52:03 -0700
From: Eric Davidson <edavidson-at-icva.gov>
To: Tesla List <tesla-at-pupman-dot-com>
Subject: Re: pole pig chart (fwd)


The kVA rating of a distribution transformer (pole pig) is a measure of
the total volt-amperes the transformer can supply on a continuous basis
(100% duty cycle).  Since many factors can effect the load current, its
doubtful you would find a chart. Distribution transformers are not the
same as NSTs or other constant current transformers. That is, a 10 kVA
pole pig will not current limit a 10 kVA, it will keep supplying current
until an over current device opens or the unit self destructs.  The
maximum short circuit current can be determined from the percent
impedance spec on the units tag.  You can easily determine the draw on
either side of the transformer using Ohms law (for unity power factor
i.e. resistive loads) and the ratio of transformation (be sure to take
the tap setting into consideration). On pole mounted, small kVA
transformers the tap changer is inside the can, it is usually labeled a
thru d, for 12.47, 13.2, 13.8, 14.4 kV. An example: if you had a 13,800
ohm resistive load (maybe several Calrod electric stove elements in
series) across a pole pig tapped for 13.8 kV, it would deliver 1 ampere
to the load and draw 13.8 kW (plus core and copper losses which may add
a couple hundred watts). The line draw would be 13,800 W/240 V = 57.5
amperes. A 10 kVA pole pig could probably supply this load all day long.
The load presented to the transformer by a Tesla coil is quite complex,
with capacitive and inductive components, definitely not a unity power
factor load.  It would be very difficult to determine the load on the
transformer and what it would draw from the 240 volt input.  My advice
is to wire the pig with 6 AWG wire and use a 60 ampere circuit breaker.
Assume that the maximum current draw would be roughly equal to an
electric stove/oven with all of the burners and the broiler on. You will
definitely want to use some inductive ballast to limit the current. Im
sure you already know this but be VERY careful with a pole pig. If you
get yourself across the HV bushings of an energized pig the best you can
hope for is deep burns, but will most likely be electrocuted. Its
nothing like the 'grab onto a spark plug wire' type shock you get from a
NST. Hope this helps! 

Eric Davidson

> ---------- Forwarded message ----------
> Date: Thu, 23 Apr 1998 23:39:57 -0500
> From: Jeff Corr <corr-at-enid-dot-com>
> To: tesla list <tesla-at-pupman-dot-com>
> Subject: pole pig chart
> I am just curious...
> does anyone have a chart showing the relationships
> between kVA of the pig, with the current it pulls on
> the 220 side if it has an output of 13.8kv or 14.4kv for
> Tesla Coil use, ex :
> size |  120 | 220 | output current
> -------------------------------------------------
> 1kVA |  12a|  6A  | 14.4kv at 120ma
> 2kVA | ??  |  ??? ??????????????????
> ....
> ...
> ...
> 15kVA
> Obviously these probably aren't the right
> values, I'm just using this as an example...
> Thanks...
> Jeff Corr
> 2114 Monitor
> Enid, OK 73703
> http://www.harvestcomm-dot-net/personal/corr/