240volt Single Phase Transformer

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  #1  
Old 07-30-06, 09:09 PM
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240volt Single Phase Transformer

Would it be wrong to think that a single phase transformer feeding the premises could be rated at 12,470 volts primary 240volts line to line/480 volts phase to phase on the secondary?

The secondary voltage reading is what I am curious about since I was told this was possible?

Thanks,
 
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Old 07-30-06, 10:59 PM
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Isn't "line to line" and "phase to phase" the same thing? What am I missing?

Did you mean 240V line to ground?
 
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Old 07-31-06, 04:45 AM
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I have never seen such a transformer. In every 277/480 three phase service I have seen there have been three 277v secondary transformers.
 
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Old 07-31-06, 02:38 PM
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Originally Posted by eeee
Would it be wrong to think that a single phase transformer feeding the premises could be rated at 12,470 volts primary 240volts line to line/480 volts phase to phase on the secondary?

The secondary voltage reading is what I am curious about since I was told this was possible?

Thanks,
I have never seen it but theoretically it is possible. with the exception of the 240 should read line (or phase but this is a misnomer) to ground.

line and phase are generally interchangable in general meaning. Boy, isn;t that a generalization of a general statement??

On a single phase system, there is only one phase but multiple lines or legs.
 
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Old 07-31-06, 04:40 PM
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If you have a 480 volt transformer with a center tap (such as would be used on a 3 wire delta hookup) then yes, you can have a 12470 volt primary with a 240 volt to neutral, 480 volt leg to leg. It's not likely you would have one on a residence though.
 
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Old 08-01-06, 04:23 AM
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Single phase transformer

Yes I had an error.

I meant to say single phase 12,470 volt primary, 240 volt line to ground/480 volt line to line secondary for the single phase transformer.

I am not talking about a 3 phase transformer. I know the 3 phase delta can be 480 volts or 240 volts using center taps, corner ground, open legs or whatever. Its been a while since I read about 3 phase deltas and never really understood it.

I was told you could have a single phase transformer with secondaries at 240vl-g/480vl-l and 277vl-g/480vl-l??? Maybe these applications are not for servicing a home, but are more industrial in nature. the line to line, l-l represents leg to leg voltages since single phase tranformers can deliver 2 legs to the facility.
 
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Old 08-01-06, 07:23 AM
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I can see that the math does work for your example. If you had a single phase secondary of 480 with a center tap neutral then line to neutral (the code would require the neutral to be grounded) would be 240.

If this animal exists, it is not common in the US. Certainly not in industrial enviornments where most systems are three phase.

If you had one of these nothing in the system would give you 277volts.

A three phase 480v delta with a center tap on one side would give you 240 from two of the three phases to neutral and I am not up at the moment to do the math for the third leg to ground, but it would be close to 480. These also may be out there, but I have never seen one.
 
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Old 08-01-06, 10:53 AM
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In 1906, Westinghouse engineered , for the New Haven Railroad, the World's first "main-line" locomotive with traction motors that operated on Alternating Current.This became known as the "single-phase" railroad electrification system which today is "standard" thruout the World.

The locomotive was equipped with a transformer with a single coil Primary winding energized with 11,000 volts.

Because a rail traction motor at rest is equivalent to a "dead" short-circuit, a reduced voltage had to be applied to the traction motors during starting. The Secondary winding of the single-phase transformer was wired with "taps" of different voltage values.

The motors at starting were switched to the transformer tap with the lowest voltage-value, and then switched to taps of sucessively higher values as the motors accelerated to full-speed.
 
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Old 08-01-06, 02:58 PM
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Originally Posted by eeee
I meant to say single phase 12,470 volt primary, 240 volt line to ground/480 volt line to line secondary for the single phase transformer.

I am not talking about a 3 phase transformer. I know the 3 phase delta can be 480 volts or 240 volts using center taps, corner ground, open legs or whatever. Its been a while since I read about 3 phase deltas and never really understood it.
I was not talking about a 3 phase transformer either. I was talking about a type of single phase transformer 480/240 that would be typically banked with two other single phase transformers to form a 3 wire delta. This type of transformer does exist. If you used it single phase you would get 240/480.

277 volt transformers typically only have two low side bushings and only supply 277 volts as a single phase device. Again, you would not typically find this unit in a single phase application. It is usually banked with two others to form a 4 wire wye, 277/480 volt bank.

On the other hand, there are rewind shops all over the U.S. and I'm sure they've all had oddball requests for unique transformers from time to time.
 
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Old 08-01-06, 03:18 PM
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You just cannot exceed the power rating of the transformer.

And you go by turn ratio. input can be anything

I don't see what is so difficult to under stand with single phase.
 
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