Re: Pole transformers wired for Three Phase (fwd)

["Tesla list" <tesla@xxxxxxxxxx>]

---------- Forwarded message ----------
Date: Tue, 7 Aug 2007 20:12:29 -0500
From: David Dean <deano@xxxxxxxxxxxxxxxx>
To: Tesla list <tesla@xxxxxxxxxx>
Subject: Re: Pole transformers wired for Three Phase (fwd)

Hi Jim

On Tuesday 07 August 2007 07:52:01 am you wrote:
> ---------- Forwarded message ----------
> Date: Tue, 7 Aug 2007 00:34:23 -0700
> From: Jim Mora <jmora@xxxxxxxxxxx>
> To: 'Tesla list' <tesla@xxxxxxxxxx>
> Subject: Pole transformers wired for Three Phase
>
> Hello All,
>
>
>
> I have seen several posts recently and in the past regarding conceptually
> how single pigs are wired while specified for single and three phase. I'm
> curious how three pigs would best be wire for 3 phase step up and what the
> ratings of the pigs should be. Reversing what the utilities do around here
> in California (three wire HV poly phase), it would seem the low voltage
> would be wired in a wye configuration and the high voltage should be delta
> connected?
>
Three pigs on a pole are wired Y-Y around here. Primary is 7200 or 14400 with 
7200 the most common.
>
> If that is the case, than should the transformers necessarily be dual
> horned and what is the appropriate transformer rating in reverse? I ask as
> I am now working in a facility that has three phase in most of the
> buildings and have a green light to pursue my Tesla coil experimentation. I
> have a 3P radar transformer with 24KV DC out but it is not as robust as 3
> pigs !!!
>
>
There are some single bushing transformers used, but the utilities like to 
keep primary as far from the pole and as far from each other as possible- 
hence the popularity of dual bushing transformers used for three phase 
services.
>
> On Richie Burnett's site he speaks of 3 phase discrete transformers using
> half and full "pulse" rectification but does not speak to the transformer
> ratings. http://www.richieburnett.co.uk/dcresist.html
>
> In this case the transformers are wired Wye to Wye which would allow me to
> use three of Dr. Resonance's transformers (the cases and one horn tied to
> ground in all three transformers). Here we have the (sqr)3 * (sqr)2 * RMS
> of a single transformer or 35Kv given 14400v transformers, yes? The
> disadvantage of the wye to wye is the PS +/- must float, isn't that so?
>
>
I don't know what half and full pulse rectification means, but the standard 
six pulse full wave three phase rectifier that gives 360Hz ripple and not 
needing a filter cap would give 20365 volts DC (+10k, -10k) and be referenced 
to ground through the windings. (and diodes I should say) The advantage to 
using 3ph to make DC is very low ripple and good regulation (so no filter 
cap) not higher voltage.

If you wanted to ground one end of the DC power supply you could leave the 
center of the "Y" ungrounded. Lets say you want to ground (-).
(-) = 0V + grounded
center of "Y" = +10kV = "floating"
(+) = +20kV = "hot"

I think most folks would consider the center of "Y" grounded safer. 


>
> So, I'm curious what would be the most desirable transformer configuration
> and voltage rating to get three phase six pulse quasi DC sans filter cap!
>
>
>
> Thanks,
>
> Jim Mora


later

deano