Phase-to-neutral voltage Uo calculation

[Mariaki]

Hi,

Could anyone please let me know how to calculate the phase-to-neutral voltage for a single phase circuit and a two phase circuit? Is it the same as for a 3-phase one, i.e. Uo=U/sqrt(3)?

Many thanks,

 

[DRWeig]

Hi Mariaki,

It depends on the configuration of the source.

If your single-phase circuit is made of two phases of a three-phase wye system, your calculation is correct.

If your single-phase circuit originates from two ends of a single-phase transformer with a center tap, the phase-to-neutral voltage will be half the phase voltage.

It would help to get a definite answer if you could post a diagram or describe your source in detail.

Good on ya,

Goober Dave

 

[Mariaki]

Hi Dave,

My question refers to the phase-to-neutral voltage for a 2 phase 500V power cable. I was also wondering what this would be for a single phase cable of 500V.

Hope this is more helpful.

Many thanks,

 

[ScottyUK]

A true two phase supply with the phases in quadrature? Or two phases from a three-phase group with a 120° phase displacement?



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If we learn from our mistakes I'm getting a great education!

 

[Mariaki]

Hi,

It is a two phase supply cable, not one from a three-phase group.

 

[davidbeach]

What does this supposed "two phase" cable connect to? What is the source. True two phase is practically non-existent. Two phases from a three phase source is vastly more common.

 

[Mariaki]

I believe it's connected to a three phase source.
Thanks in advance

 

[ScottyUK]

For a true two phase system the line-neutral voltage will be V_line/[√]2.

I agree with David - there's not much 2-phase stuff left. I think there was some in the outlying parts of north-east England but even that might have gone by now.


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If we learn from our mistakes I'm getting a great education!

 

[Mariaki]

thanks for this! Actually it is a cable within an umbilical powering a motor, if this makes more sense. I have not been given the exact source type though. However, the umbilical contains 3-phase cables as well so I would assume all cables should be powered from the same source. I've read about the Scott transformer, used to supply 2-phases from 3-phases. In that case, should I divide with the transformer ratio, i.e. 0.5*sqrt(3) (

http://en.wikipedia.org/wiki/Scott_connection)?

 

[waross]

I can think of three possible configurations from your description.
The term ground is often used to indicate neutral. Are you using the term neutral to indicate ground?
My best guess is that you have a single phase circuit fed from two phases. You don't have a neutral but the voltage to ground of either line MAY be (Line to line Voltage/Root Three)
or, for 500 Volts, 289 Volts.

Bill
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"Why not the best?"
Jimmy Carter