Single Phase Theroy

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jim dungar

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Wisconsin
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No place in the US is intentionally setting up SWER systems.
You are correct in the present tense.

However, there was a time they were used, but normally only on very rural systems. It is possible, but extermely unlikely to currently find one in a major urban area.
 

iwire

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Location
Massachusetts
Well there's only one wire up there and the lights still come on... so if you can tell me what else it could be i'm listening
I assume you have not seen one of the conductors.

If you can find any evidence of public utility owned, intentionally set up SWER systems in the US I would be listening. :)
 

LarryFine

Master Electrician Electric Contractor Richmond VA
Well there's only one wire up there and the lights still come on... so if you can tell me what else it could be i'm listening
There may be only a single distribution conductor between poles, but there should also be a grounded conductor. It may be the neutral of a triplex, but it should be there.

Where in B'more are you? Got pix?
 
I assume you have not seen one of the conductors.

If you can find any evidence of public utility owned, intentionally set up SWER systems in the US I would be listening. :)
You a cop or sumpthin?

:D

We are looking at SWER to use to provide power to Alaska's widely dispersed rural villages. Unfortunately, the National Electric Safety Code does not allow single wire earth return for AC or DC over extended periods.
From: http://www.ruralpower.org/index.php?option=com_content&view=article&id=22:swer-frequently-asked-questions-1&catid=9:faq&Itemid=11
 

jcormack

Member
Location
Pennsylvania
Power

Power

I have always used this argument when asked about single -vs- two phase on 120/240.
Yes, the current waveforms are 180 degrees out of phase with each other when using neutral (ground) as the reference - but so are the voltage waveforms. The resultant POWER waveforms though are identical (neg * neg = pos)- The POWER is in the same time phase in both legs of the 120/240.
 

nicholaaaas

Member
Location
Baltimore
There may be only a single distribution conductor between poles, but there should also be a grounded conductor. It may be the neutral of a triplex, but it should be there.

Where in B'more are you? Got pix?
I most certainly isn't triplex... as there is only one bare metallic wire going to this transformer. And it being ascr wouldn't explain a metallic return if there is only one wire up there. It could be possible they share a ground with the telco services. But i highly doubt that.

The area I'm talking about is in Catonsville. The primary feed runs from a street about a quarter mile away. and runs between the rear property lines of houses on two separate streets. the house were built in the 50's so maybe they would have been allowed back then to run short swer lines off their standard distributions back then?
 

jim dungar

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I most certainly isn't triplex... as there is only one bare metallic wire going to this transformer. And it being ascr wouldn't explain a metallic return if there is only one wire up there. It could be possible they share a ground with the telco services. But i highly doubt that.
It is possible that the transformer has only a single bushing, one hot wire, and the other connection is to a ground on the pole (this is probably an MGN or multi-grounded neutral system). The key to it actually being an SWER is how many conductors are strung from one pole to the next.
 

nicholaaaas

Member
Location
Baltimore
It is possible that the transformer has only a single bushing, one hot wire, and the other connection is to a ground on the pole (this is probably an MGN or multi-grounded neutral system). The key to it actually being an SWER is how many conductors are strung from one pole to the next.
One bare conductor
 

hurk27

Senior Member
One conductor on insulators and absolutely no other continuous wire, even pole to pule 'guy' wires, is definitely rare. Can you post pictures?
I have seen in other states where the telco or cable company will use the MGN for their messenger wire to hang their cable from, and make it look like there is no MGN, and I'll bet this is the case as shown high lighted in red below:

I most certainly isn't triplex... as there is only one bare metallic wire going to this transformer. And it being ascr wouldn't explain a metallic return if there is only one wire up there. It could be possible they share a ground with the telco services. But i highly doubt that.

The area I'm talking about is in Catonsville. The primary feed runs from a street about a quarter mile away. and runs between the rear property lines of houses on two separate streets. the house were built in the 50's so maybe they would have been allowed back then to run short swer lines off their standard distributions back then?
 

rattus

Senior Member
Half right!

Half right!

Hello everyone btw. One day a co-worker and I were talking and he asked why do they call it single phase when there are two hot wires. I though about it for a minute and answered because it actually IS only one phase. It comes from your power supplier on only one line, It goes through a transformer the secondary coil is connected between the two outer taps, and the middle of the coil is center-tapped to get a mid point. Therefore it is single phase 240 with a grounded mid point.

When I asked my apprenticeship teacher he started drawing a picture of two sine waves 180? apart. And insisted it really was two distinct phases.

Who's right?
Don't know what else has been said here, but the voltages, V1 and V2, on L1 and L2, relative to the CT, are indeed 180 degrees apart as the sine waves indicate.

However, it is incorrect to imply that this is a 2-phase system because the extra "phase" is created by a simple inversion--not a second generator.

In other words:

The voltages, V1n and V2n, in a 120/240V 1-phase sytem are separated by 180 degrees.

The separation in the obsolete 2-phase system is 90 degrees, and a minimum of 3-wires and 2 transformers are required.
 

buffnitup

Member
According to textbooks. Single phase is derived from 1 phase stepped down to 240V from about 7200V via a transformer. Once the transformer is center tapped(neutral/grounded) in the winding. The voltage is split. 120V on 1/2 of the winding and 120V on the other 1/2. These two are added using vector addition equaling 240V. These voltages are 180 degrees out of phase with each other. Not sure why they are opposite from each other but...
 
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jim dungar

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Location
Wisconsin
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Engineer
The voltages, V1n and V2n, in a 120/240V 1-phase sytem are separated by 180 degrees.
The voltages V1n and Vn2 are not separated by 180?.

So a 120/240 system is:
Two single-phase voltages connected in series so that the voltages add. The presence or absence of a neutral is immaterial.
 

wasasparky

Senior Member
Use the hill analogy:
You are standing at the bottom of a 240? hill. You are looking at one hill.

Walk half way up the hill. How many hills are there?
Some say one 240? hill that you are standing half way up.
Some say two hills? A 120? hill up, and a 120? hill down?

Now that I think about it, are you half way up the hill? or half way down the hill?
 

rattus

Senior Member
Yes and no:

Yes and no:

The voltages V1n and Vn2 are not separated by 180?.

So a 120/240 system is:
Two single-phase voltages connected in series so that the voltages add. The presence or absence of a neutral is immaterial.
You are half right Jim, but that is not what I said. I said V1n and V2n are separated by 180 degrees. This is easily demonstrated with a dual channel scope. I would not measure Vn2 with a scope because V2n would be shorted to the EGC.

But you are wrong on the neutral. If there is no neutral, then the subscript "n" is meaningless and we can only measure V12 and V21 which are also separated by 180 degrees.
 
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