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Re: Pole Pig Question: (fwd)



Original poster: List moderator <mod1@xxxxxxxxxx>



---------- Forwarded message ----------
Date: Fri, 25 May 2007 19:14:17 +0000
From: David Rieben <drieben@xxxxxxxxxxx>
To: Tesla list <tesla@xxxxxxxxxx>
Cc: drieben@xxxxxxxxxxx
Subject: Re: Pole Pig Question: (fwd)

Hi all,

I suppose that would depend on how one defines "center-tapped".
I think what Aaron is saying is that a standard single phase, 120/
240 volt output, pole mounted distribution transformer i.e. "pole
pig" does NOT have a single 240 volt secondary winding that is
center-tapped inside the transformer's secondary coil from the
factory. It does have two seperate 120 volt secondary windings. 
However, if one serieses the two seperate 120 volt secondary
windings and grounds the common lead of the two secondary
windings (the way most residential service pole pigs are internally 
wired), it is "electrically" a center-tapped 240 volt transformer with 
the common lead grounded and thus 120 volts from each outer "hot" 
lead to the grounded common or 240 volts between the two "hot"
outer leads.


David Rieben

-------------- Original message -------------- 
From: "Tesla list" <tesla@xxxxxxxxxx> 

> Original poster: List moderator 
> 
> 
> 
> ---------- Forwarded message ---------- 
> Date: Fri, 25 May 2007 10:01:09 -0700 (PDT) 
> From: J. Aaron Holmes 
> To: Tesla list 
> Subject: Re: Pole Pig Question: (fwd) 
> 
> You really shouldn't refer to pole pig secondaries as 
> "center-tapped". For the average U.S. 120/240V pig, 
> that is simply not true. There are *two* 120V 
> secondaries configured in parallel or series according 
> to the service type, as I explained in my prior mail. 
> If there really was only a single center-tapped 
> secondary, this would not be possible. 
> 
> Actual "center taps" in distribution transformers seem 
> to be, in reality, a bit unusual. The most common use 
> of a center tap that *I've* seen is on 240V delta 
> three-phase transformers, where one of the 240V 
> windings is sometimes center-tapped to provide 120V 
> without the requirement of a separate transformer. 
> 
> Cheers, 
> Aaron, N7OE 
> 
> 
> --- Tesla list wrote: 
> 
> > Original poster: List moderator 
> > 
> > 
> > 
> > ---------- Forwarded message ---------- 
> > Date: Fri, 25 May 2007 10:40:53 -0400 
> > From: Jonathon Reinhart 
> > 
> > To: Tesla list 
> > Subject: Re: Pole Pig Question: (fwd) 
> > 
> > OK, I guess I was a *little* off... but the general 
> > idea was right... I 
> > think... :-P 
> > 
> > Sorry for any confusion... 
> > 
> > Jonathon 
> > 
> > On 5/25/07, Tesla list wrote: 
> > > 
> > > Original poster: List moderator 
> > > 
> > > 
> > > 
> > > ---------- Forwarded message ---------- 
> > > Date: Fri, 25 May 2007 08:24:11 -0400 
> > > From: Jonathon Reinhart 
> > 
> > > To: Tesla list 
> > > Cc: rrreinhart@xxxxxxxxx 
> > > Subject: Re: Pole Pig Question: (fwd) 
> > > 
> > > I always thought it was best to look at it first 
> > as just what you said: 1 
> > > Primary (HV) = 1 Secondary. 
> > > 
> > > X1 X2 
> > > O O 
> > > | | 
> > > vvvvvvvvvvvvvv HV 
> > > ========= 
> > > ^^^^^^^^^^^^^^ LV 
> > > | | | 
> > > O O O 
> > > L1 N L2 
> > > \ / \ / 
> > > 120 120 
> > > 
> > > Remember the secondary coil is center-tapped, so 
> > for now, just think about 
> > > the secondary coil as a whole. The voltage 
> > waveform across L1 and L2 will 
> > > look exactly like the waveform across X1 and X2, 
> > just as one would expect. 
> > > The tricky part comes in when you add that 
> > centertap, and the confusion is 
> > > this: Voltage is relative. Now without any 
> > grounds connected, all of 
> > > these 
> > > voltages on the LV side are simply relative to 
> > each other (I think they 
> > > might float at whatever actual voltage they wish). 
> > But L1-L2 is 240VAC, 
> > > L1-N is 120VAC and L2-N is 120VAC. 
> > > 
> > > Now, we ground one of the terminals so that the 
> > voltage is stable and has 
> > > a 
> > > reference point. We COULD (but don't), decide to 
> > ground L1. In this case, 
> > > we could get 120V to ground at N, and 240V to 
> > ground at L2. In this case, 
> > > when N was at +120V, L2 would be at +240V (and 
> > same for the negative 
> > > side). 
> > > 
> > > However, it makes much more sense to ground that 
> > centertap. Now the 
> > > difference between L1-N is 120VAC and L2-N is 
> > 120VAC, but at a given 
> > > instant 
> > > when L1 is at +120V to ground, and L2 is at -120V 
> > to ground, because they 
> > > are wound the same direction, but on opposite 
> > sides of the centertap. We 
> > > ground this center tap, because now, we can still 
> > get 240VAC by connecting 
> > > to L1 and L2, but we can never get more than 120V 
> > to ground, which is 
> > > safer. 
> > > The only way to get a 240V shock is to touch both 
> > L1 and L2, which is 
> > > well, 
> > > pretty unlucky. 
> > > 
> > > Hope this helped, 
> > > 
> > > Jonathon 
> > > 
> > > On 5/24/07, Tesla list wrote: 
> > > > 
> > > > Original poster: List moderator 
> > 
> > > > 
> > > > 
> > > > 
> > > > ---------- Forwarded message ---------- 
> > > > Date: Thu, 24 May 2007 16:14:32 -0500 
> > > > From: Jim < branley1@xxxxxxxxxxx> 
> > > > To: tesla-request@xxxxxxxxxx, Tesla list 
> > 
> > > > Subject: Pole Pig Question: 
> > > > 
> > > > 
> > > > Hi Folks: 
> > > > 
> > > > I have received from you a bucket truck load of 
> > insightful input on pole 
> > > > pigs that has helped me to better understand 
> > them, thanks. 
> > > > What seems to be evading me is How can a single 
> > primary feed create 2 - 
> > > > secondaries that are alternating in current. 
> > > > I always assumed that 1 - primary feed equals 1 
> > - secondary wave form 
> > > > not 2 - alternating wave forms. 
> > > > 
> > > > Your help is greatly appreciated, 
> > > > 
> > > > Jim 
> > > > 
> > > > 
> > > > 
> > > > 
> > > 
> > > 
> > > 
> > 
> > 
> > 
> 
> 
>