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Re: Pole Pig Question: (fwd)
Original poster: List moderator <mod1@xxxxxxxxxx>
---------- Forwarded message ----------
Date: Mon, 28 May 2007 12:55:36 -0500
From: Jim <branley1@xxxxxxxxxxx>
To: Tesla list <tesla@xxxxxxxxxx>, Tesla list <tesla@xxxxxxxxxx>
Subject: Re: Pole Pig Question: (fwd)
Thank you for the effort:
I believe that I am starting to get it. Picture 1 - primary alternating
at 60hz, picture 1 - secondary outputting 240volts or 2 - series
secondaries each outputting 120volts or both of the ends tied together
at one end and the other two ends outputting 240volts. They are in phase
with each other? The 2 - secondaries are out of phase because they are
wound differently?
Thank you once again,
Jim
Tesla list wrote:
> 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
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>
>>>>
>>>
>>>
>>
>>
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