Re: buying a pole pig, wye and delta

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: "Gerry  Reynolds" <gerryreynolds@xxxxxxxxxxxxx>

Hi Jim,

Lets say you have a Y distribution going between points A and B with 
the center node also going between points A and B.  If the currents 
in each of the three phases are the same, the center node connection 
will carry no current.  If the load currents are not balanced, the 
three phase sum of the currents will be returned by the center connection.

Y connected source will make the absolute voltage (wrt ground) of 
each phase the same.  Delta connected source will make the difference 
of voltage between any two phases the same.  You can think of a delta 
sourced distribution as one of three loops for three phases A, B, and 
C.  Loop 1 involves the load between phase A and B.  Loop 2: phase B 
and C.  Loop 3: phase C and A.  Each loop current is dependent on the 
load for that loop. The total current in the wire for phase A will be 
the current for loops 1 and 3 since the wire is not only carrying the 
load current  for one loop but the return current for the other loop

Gerry R..

> Original poster: "Jim Mora" <jmora@xxxxxxxxxxx>
>
> Please explain what you mean by balancing being made up by the ground path
> in a wye configuration. Since wye can be connected two BTW 2 phases rather
> than to ground or for that matter a large load to any one ground. How does
> this "balance things out load wise?
>
> As you may know I'm build a three phase generator 20KVA delta 480v. This
> will feed a delta to wye 208/120v transformer. My understanding that this
> arrangement cleans up harmonics and make a closer to clean sine wave output.
>
> This in turn can be used for emergency power or what I'm building it for is
> a wye input configured 3 phase HV transformer.
>
> I fail to see how load balancing is accomplished however.
>
> Thanks for your input,
> Jim Mora
>
> -----Original Message-----
> From: Tesla list [mailto:tesla@xxxxxxxxxx]
> Sent: Tuesday, June 06, 2006 11:10 PM
> To: tesla@xxxxxxxxxx
> Subject: Re: buying a pole pig
>
> Original poster: "Gerry  Reynolds" <gerryreynolds@xxxxxxxxxxxxx>
>
> Hi David,
>
> If the delta system was 12470 across two of the three phases, this
> would be identical to a Y system that had 7200V in each leg
> (referenced to ground) in that the voltage across two of its three
> phases would also be 12470V. Sounds like if the pig were hooked to
> 7200V across its 2 HV bushings and delivered 120Vac on the parallel
> LV configuration, then it would deliver 208 Vac in the same LV
> configuration when hooked across 12470V on the HV side. If one were
> to drive the LV with 240V in the parallel LV configuration, the
> output would be 14400V.  If the core can safety take the 12470/208
> without saturating then maybe there's hope for the 14400/240 operation.
>
> In terms of the sematics of the meaning of 12470Y,  one could connect
> the pig across two phases of a Y system just as easily as a delta
> system so maybe this nomenclature is just fine.  BTW, what is common
> in the USA, Y or delta or both??  With delta, the loads across each
> pair of phases needs to be balanced else the currents on one of the
> phases could be excessive.  In a Y system, any unbalanced currents
> are made up for by the ground path.
>
> Gerry R.
>
>
>
>
> >Original poster: DRIEBEN@xxxxxxxxxxxxxxx
> >Gerry,
> >
> >I am no EE or a specialist in electrical
> >power distribution but it is my understanding that
> >the "Y" rating is only for a 3-phase delta hookup
> >where the input HV bushings are just crossed between
> >two of three phases. I agree with what Mike Marcum
> >also stated in that the "Y" rating is actually the
> >"delta" voltage rating and it seems that pigs "Y"
> >rating should actually be the lower of the voltages
> >(12470/7200Y as opposed to 12470Y/7200) since the
> >12470 volts would only be seen in a delta cross
> >phase hookup.
> >
> >David Rieben
> >
> >----- Original Message -----
> >From: Tesla list <tesla@xxxxxxxxxx>
> >Date: Tuesday, June 6, 2006 1:55 pm
> >Subject: Re: buying a pole pig
> >To: tesla@xxxxxxxxxx
> >
> > > Original poster: "Gerry  Reynolds" <gerryreynolds@xxxxxxxxxxxxx>
> > >
> > > Hi David,
> > >
> > > Seems lik........