TWO PHASE MOTOR

[winston1]

I understand about the 220v 2 phase USA system,

You clearly don't, because as has already been explained it is 240v.

 

[JohnW2]

Such quibbling is only going to confuse the OP

 

[bernardgreen]

Incidentally, the Motor has 3 connections marked 240v - N- 240v and earth.

Any chance of a photo ? I assume the machine in the UK and being used on a 240 volt single phase supply.

There is a 240v to 110v step down transformer in the machine

Machinery imported from the US to the UK often has a 240 -> 110 transformer fitted to supply most of the machine's circuits as this is cheaper than changing most of the electrical items to be 240 volt devices. Where the machine also has 240 volt items that would use a 2 phase supply in America the machines wiring is altered to connect these 240 volt items to the UK single phase and Neutral

In the UK ~ Neutral----MOTOR----Phase
In the USA ~ Phase 1----MOTOR----Phase 2

 

[BQW]

You clearly don't, because as has already been explained it is 240v.

OK, I pressed the wrong button, 240v.
So what you are stating is that the USA 240V supply is not, as I had previously been informed a two phase supply, but a 120v-0-120v, with both 120`s being in phase, and any 240v appliance or load is connected between.
Hence, the need for the start cap.
That all makes sense , and the conclusion is it must be a single, not a two phase motor ? But why then has it got 3 connections excluding the earth, they are, a red wire marked L2, white wire marked N and black wire marked L1.
Incidentally, I always thought the two output`s of any centre tapped transformer were 180 deg out of phase, is that not correct either ?
I will put my double beam scope across a 110v site Tx tomorrow at work and have a look at the phase shift, if any.

 

[JohnW2]

So what you are stating is that the USA 240V supply is not, as I had previously been informed a two phase supply, but a 120v-0-120v, with both 120`s being in phase, and any 240v appliance or load is connected between.

No, just as with a UK 240-0-240 'split phase' supply (which the Wiring Regulations call '2-phase', even though a good few here say that is 'wrong'), relative to the "0" the two 120s are 180° out of phase.

Incidentally, I always thought the two output`s of any centre tapped transformer were 180 deg out of phase, is that not correct either ?

As above it IS correct, in that the voltage of the two outputs, relative to the centre tap, are 180° out of phase.

I will put my double beam scope across a 110v site Tx tomorrow at work and have a look at the phase shift, if any.

... and again, if you connect the 'common' of your scope to the centre tap of a transformer secondary (which is what will happen implicitly if the centre tap and the common of your 'scope are both earthed) and examine the voltages at the two ends of the secondary, you will find that they are 180° out-of-phase.

Kind REgards, John

 

[BQW]

No, just as with a UK 240-0-240 'split phase' supply (which the Wiring Regulations call '2-phase', even though a good few here say that is 'wrong'), relative to the "0" the two 120s are 180° out of phase.
As above it IS correct, in that the voltage of the two outputs, relative to the centre tap, are 180° out of phase.
... and again, if you connect the 'common' of your scope to the centre tap of a transformer secondary (which is what will happen implicitly if the centre tap and the common of your 'scope are both earthed) and examine the voltages at the two ends of the secondary, you will find that they are 180° out-of-phase.

Kind REgards, John

Thanks John,
I was beginning to think every thing I learnt in the 70`s was wrong.

 

[Diver Fred]

PM Sent

 

[bernardgreen]

But why then has it got 3 connections excluding the earth, they are, a red wire marked L2, white wire marked N and black wire marked L1.

The white wire marked N. Does it attach to a terminal and if so then does that terminal have a wire or connection into the motor ?

When a standard cable is used to bring 240 volt power to a location then a Neutral conductor will often be included in the cable. If the appliance does not need the Neutral it still should provide an anchor terminal for safe termination of that conductor. Better than that wrapping the end in insulation tape.

In America the Live wire ( aka Hot wire ) is Black and the Neutral is White.

 

[ericmark]

Even with a generator zig zag wired where you clearly have all three phases since no access to individual phases it's called single phase, with 230 - 0 - 230 we call it split phase when it comes from a single phase transformer and twin phase from a three phase transformer simply because the combined voltage is 460 or 400 and there is a need to realise the difference in the combined voltage. However with 55 - 0 - 55 and 64 - 0 - 64 we simply call them both 110 volt, as with zig zag wired you should not be using the phases independently, the only point is with a triple 16A MCB you can draw around 30 amp total once split into three sockets you can draw approx 10A each socket.

As to motors, with a single phase motor as it is called we produce a second phase at lease to start it so in real terms it is a two phase motor, even if second phase generated in the motor, my fridge freezer has a three phase motor even when the supply is single phase, the inverter turns it to three phase, and no different with old type single phase motor the capacitor turns it to single phase.

Be it wrong or correct the terminology is used to help us recognise what we are working with, so we call it a fused spur, even through it is a radial to differentiate between radial from distribution box and radial from a final circuit even the name ring final does not mean it's the final distribution system but shows it is the type of ring which should not be split. We often add the word electronic to transformer, or ballast in same way to help work out what we have, if you went to B&Q and asked for a pulse width modulated power supply for use with quartz lighting they would look at you rather strangely and likely have not a clue what you wanted.

As above it IS correct, in that the voltage of the two outputs, relative to the centre tap, are 180° out of phase.

That is of course true, but relative to either end they are in phase and if we look at a transformer with 8 voltage tappings we would not call it a 9 phase transformer, it is still single phase.

So it is not wrong to call a split phase supply twin phase, but it can cause problems if the user expects to find 64 - 0 - 64 and instead gets 55 - 0 - 55 from the 110 volt supply.

As to USA being 120 volt well we are claimed to be 230 volt but until solar panels most homes were 240 volt, it does mean there is a better interchangeability between 120 volt 60 Hz and 110 volt 50 Hz as transformers tend to work on either, although theory says their different.

So in conclusion and non commutated motor is likely twin phase, at least to start it, so the name twin phase motor may be correct, but it does not really help describing a motor that way. One may be able to use two phases to cause a motor to start and run, however I have never seen a motor designed to run on two phases, often seen motors running on two phases, but the turning of the motor actually generates a third phase, and normally makes more noise and over heats.

I am sure some where there will be a special, I remember telling store-man you do get 8 volt lead acid batteries for starting earth movers, and loosing £5, there always seems to be an exception to the rule, but in my travelling around the world I have not seen one.

 

[ericmark]

Machinery imported from the US to the UK often has a 240 -> 110 transformer fitted to supply most of the machine's circuits as this is cheaper than changing most of the electrical items to be 240 volt devices. Where the machine also has 240 volt items that would use a 2 phase supply in America the machines wiring is altered to connect these 240 volt items to the UK single phase and Neutral

In the UK ~ Neutral----MOTOR----Phase
In the USA ~ Phase 1----MOTOR----Phase 2

I have seen USA imports, and also seen them rejected due to the difference in what they call 120 volt and what we call 110 volt, we require the centre tap to earth, so we had a load of lighting sets with 110 volt outlets, then we found the 110 volt was not centre tapped it was taken off a centre tap so the generator was 110 - 0 - 110 it seems the question had be raised before buying "is this a centre tapped supply", and answer had be yes, and it was centre tapped but not the centre tapped needed for UK. All 110 outputs had to be blanked off, tried to get 110 to 55 - 0 - 55 volt transformers however they would need to be specials and so very expensive, and two phases were 190 volt not 220 volt so again needed special transformer, cheapest option was two transformers one 110 to 230 and second 230 to 55 - 0 - 55 so simply blanked off outputs and used as lighting sets only.

The firm had employed an Australian electrician very cleaver guy, however he did not know all UK rules and regulations, so got caught out with these units.

Also it seems USA have many different types of supply, with some historic use of DC, and delta outputs from supply transformers with one winding centre tapped and bonded to earth, the phase not directly connected to earth was called the hot phase, I am told, so I am very wary of USA stuff, had to work with it in Hong Kong, and 220 volt delta IT supplies are really hard to work with. I can see why they are not allowed here. Only IT supply I have seen used in UK is the shaver socket.

 

[bernardgreen]

This is a cartoon from https://hackaday.com/2016/02/22/a-field-guide-to-the-north-american-utility-pole/

but it is not that far from the reality of when extra tin can transformers have to be hung on poles to supply a few extra houses or offices.

This is a fairly typical set up of three single phase transformers converting ( probably ) 10kV 3 phase delta to 4 wire 3 phase star.

 

[JohnW2]

Thanks John, I was beginning to think every thing I learnt in the 70`s was wrong.

You're welcome.

What you need to understand (and probably now do!) is that all the discussions/ debates/ arguments/ quibbling/ differences are about terminology, no the physics (which certainly hasn't changed since the 70's - or since any other point in time!).

Kind Regards, John

 

[JohnW2]

... with 230 - 0 - 230 we call it split phase when it comes from a single phase transformer and twin phase from a three phase transformer ....

I suppose that begs the further terminological question as to what one means by a "single phase transformer" and a "3-phase transformer".

"Twin phase" is a new one on me, but I presume you're simply talking about 2 of the 3 phases of a 3-phase supply - something which (per the diagram I posted above) BS7671 still calls "2-phase (120°)". However, although I may be wrong, I would seriously doubt that any equipment/load would be designed to work off such a supply - so maybe it's rather 'hypothetical'?

That is of course true, but relative to either end they are in phase and if we look at a transformer with 8 voltage tappings we would not call it a 9 phase transformer, it is still single phase.

I think you may be missing the point. ....

... no matter how many taps there are the voltages at any two of them, relative to any tap in between them, will be 180° out-of-phase with each other - hence arguably (and as per BS7671) "2-phase" in any/every case.[/QUOTE]

Kind Regards, John

 

[Deleted member 18243]

I will ask an American aquaintance, he is a service engineer aquaintance who roams the Eastern Seaboard.

Is he a lineman for the county?

 

[bernardgreen]

Is he a lineman for the county?

Someone had to say it ......well done. But he doesn't go as far west as Kansas CLICK