Purpose of 110V 3 phase?

electricnova · Oct 27, 2022

Hi,

I have taken over a design engineering job for industry.

The design is using a 400V/110V transformer. Usually, the 110V is single phase. However, in this case it is giving 110V 3 phase 32A.

The 110v 3 phase is for use with 4P 110V socket to run a pump.

Being in the UK, I am used to seeing 110V single phase for this application.

Can someone explain why the 3phase option will have been chosen instead?

Any diagrams will be welcomed.

Thank you

snowhead · Oct 27, 2022

Is the pump something specialised that's only available 3ph 110v?
Or is it in a Special location where the customer has specc'd 110v 3ph?

electricnova · Oct 27, 2022

snowhead said:
Is the pump something specialised that's only available 3ph 110v?
Or is it in a Special location where the customer has specc'd 110v 3ph?

Hi, this information is not currently available - awaiting a customer reply. The pump is just a vacuum pump which we normally use single phase for.

I wondered if there were unknown reasons for use of 3 phase instead?

littlespark · Oct 27, 2022

110V such as power tools on building sites are 110V split-phase...Not single phase
ie, there is only 55V to earth, but 110 between the two.

James · Oct 27, 2022

is it 110v between phases or 110v from phase to N?

a lot of equipment from Japan runs on (don't hold me to the numbers here) about 200v phase to phase, that gives around 115v phase to N.
not unusual in machine building circles but i don't see a reason for using it to supply a pump unless there is not an alternative available for 400v

electricnova · Oct 27, 2022

littlespark said:
110V such as power tools on building sites are 110V split-phase...Not single phase
ie, there is only 55V to earth, but 110 between the two.

Thanks. On all manufacturers data and our equipment schedules it is referred to as single phase.

Split phase and single phase (3 wire) I believe are the same.

55v to earth is the usual configuration with centre tapped to earth

However you can have the neutral to earth to have the full 110v to earth instead

(this is the configuration in my original post)

James · Oct 27, 2022

Split phase is not the same as single phase.
split gives you 2 phases 180degrees apart.

single phase obviously has no phase difference angle.
3 phase has 3 x phase voltages 120degrees apart.

your original post is about 110v 3 phase
however you have just mentioned that you are talking about 110v from phase to earth is this 3 phase? If so then it would be about 200v phase to phase.

a drawing or spec sheet would be really useful at this point.

electricnova · Oct 28, 2022

James said:
Split phase is not the same as single phase.
split gives you 2 phases 180degrees apart.

single phase obviously has no phase difference angle.
3 phase has 3 x phase voltages 120degrees apart.

your original post is about 110v 3 phase
however you have just mentioned that you are talking about 110v from phase to earth is this 3 phase? If so then it would be about 200v phase to phase.

a drawing or spec sheet would be really useful at this point.

Sorry, I made an incorrect statement above.

I am looking to understand 3ph 110v.

However, this thread has made me question my understanding of 110v not 3ph (not sure what to call it at this point).

Why is it that manufacturers refer to 110v as single phase? I have attached examples

James · Oct 28, 2022

Three-Phase Power Explainer Video

Take a close look at three-phase power and receive an explanation on how it works.

www.raritan.com

the voltage makes no difference to how many phases there are.

loz2754 · Oct 28, 2022

That motor is 3hp not 3ph. Just to state the obvious...

electricnova · Oct 28, 2022

loz2754 said:
That motor is 3hp not 3ph. Just to state the obvious..

Yep, I used that as an example, it is not the one for my 3ph question.

electricnova · Oct 28, 2022

James said:
Three-Phase Power Explainer Video

Take a close look at three-phase power and receive an explanation on how it works.

www.raritan.com

the voltage makes no difference to how many phases there are.

Thanks for your time.

I understand more now. I will ask my university lecturer to give me a full explanation. I just checked through my uni notes and we havent gone over any 110v applications.

electricnova · Oct 28, 2022

To summarise my understanding.

The video explains a 400v 3 phase line will give the 230v single phase that we use in homes which i understand. And mentions the 110v single phase is from a 308v 3phase line (used in american homes).

So being in the UK with a 400V 3ph supply (230v single phase)... We add a transformer 400V 3ph/110V 1ph or 3ph, this means that the way we have achieved 110V is just through the step-down windings in the transformer with the secondary side either centre tapped to earth or neutral earthed.

Then we can either connect to one phase or three phase on the secondary side depending on the application?

Apologies for any complications along the way.

brianmoooore · Oct 28, 2022

You can connect any single phase motor of the appropriate voltage to a 3 phase supply, either by connecting it across two of the phases or between one of the phases and neutral (if present).
There is actually no such thing as a single phase motor, since it would not start. Single phase motors use a capacitor to create a different phase and feed that to a second winding to provide a starting torque. After the motor is running the second winding as capacitor are often disconnected.
Single phase motors tend to be less reliable, more expensive and have inferior starting characteristics to three phase ones, so three phase is normally used when available.

electricnova · Oct 28, 2022

brianmoooore said:
You can connect any single phase motor of the appropriate voltage to a 3 phase supply, either by connecting it across two of the phases or between one of the phases and neutral (if present).
There is actually no such thing as a single phase motor, since it would not start. Single phase motors use a capacitor to create a different phase and feed that to a second winding to provide a starting torque. After the motor is running the second winding as capacitor are often disconnected.
Single phase motors tend to be less reliable, more expensive and have inferior starting characteristics to three phase ones, so three phase is normally used when available.

ah yes, I recall this. I have only ever learned about 3 phase and so any mention of single phase I feel I don't have much understanding in a practical or theoretical sense. All I learned was how we achieve the standard 230v single ph really.

As for motors, again, only learned the 3 phase theory. Which coincides with your explanation of single phase motor as the rotation will need to be initiated. I imagine it to be similar to requiring a DC supply to a synchronous machine, in the sense of something being needed to start rotation.

Cheers

Purpose of 110V 3 phase?

electricnova

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snowhead

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James

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Three-Phase Power Explainer Video

loz2754

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Three-Phase Power Explainer Video

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