Urgent, need advice please. What's the difference between 1, 2 and 3 phase power?

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Dear Brains Trust,

I'm inthe process of buying a place that was advertised as having 3 phase power to the shed. Turns out it doesn't and it'll cost $50,000 to put it there. (long story)

The sparkie says it has "two phase power" and there's an odd looking plug that suggests something like that could be true.

Other claims include: there being 500 volts to the shed; there are 30-40 odd amps to draw on; and that it was set up for a "cocky's (farmer's) welder" - something I've never seen in any tool catlogues.

Questions:


  • My compressor and welder are 15 amps, single phase. I had ideas I might get me a lathe and or a milling machine do I need 3 phase.
  • What would I need 3-phase for anyway?
  • Are the modern non-industrial/light duty machines set up to used single phase?

Any comments greatly appreciated,

P
 
Last edited:
Exfrogger said:
Dear Brains Trust,

I'm inthe process of buying a place that was advertised as having 3 phase power to the shed. Turns out it doesn't and it'll cost $50,000 to put it there. (long story)

The sparkie says it has "two phase power" and there's an odd looking plug that suggests something like that could be true.

Other claims include: there being 500 volts to the shed; there are 30-40 odd amps to draw on; and that it was set up for a "cocky's (farmer's) welder" - something I've never seen in any tool catlogues.

Questions:


  • My compressor and welder are 15 amps, single phase. I had ideas I might get me a lathe and or a milling machine do I need 3 phase.
  • What would I need 3-phase for anyway?
  • Are the modern non-industrial/light duty machines set up to used single phase?

Any comments greatly appreciated,

P
Click to expand...

Some basics:

Three phase power has a neutral wire and three active wires.
The voltage with respect to neutral of each active wire is 240 volts.
The voltage between any two of the active wires is 415 volts

Thus if you have two active wires and a neutral wire you have two lots of single phase or "two phase"

Similarly if you have one active wire and one neutral wire you have "single phase"

If you have a neutral and three active wires you have "three phase".

Now there is more. In the case of three phase equipment there is two methods to connect to the "load" ie lathe, compressor etc.

If the three phases are connected without using the neutral wire the load is said to be delta connected.
If the three phases and neutral are connected the load is said to "star" (or wye) connected
Most hardcore motors use the former.

Look at the incoming fuses on the fascia. The number of fuses is the the number phases . You probably have two service fuses.

Two phase it good. It gives double the current capability of an equivalent single phase supply.

It also lets you use 415 volts ( this is the voltage between the two actives) equipment (not three phase tho'). Some welders made for farms are 415 volt units.

I suggest you stick with single phase equipment because it more universal in domestic situations. These day you can get three HP single phase motors which are suitable for medium size mills and lathes.

It's hard to cover every aspect in a short post.:)
 
Thanks Rob, I had hoped you'd reply.

I gather then there's not much in the way of 415v equipment out there these days and other than welders I may have no use for 2 phase.

If 15 amp single phase will do the trick then that might be all I need.

All the best

Peter
 
This is a bit of a grab bag of ideas, sorry.

The only real benefit of 3 phase power for someone with what I imagine to be your needs (serious hobbyist) is that you can buy old 3 phase equipment more cheaply than equivalent old 3 phase equipment. Single phase equipment will meet your needs. You don't need a big motor to drive a lathe. Mine has a 1 hp motor and it is quite enough. Similar story for a mill. Even my giant drill press and heavy grinder have only 2 hp motors, and I can't imagine you needing anything that big.

In many rural areas so-called 2 phase power is not 2 phases of a 3 phase supply with 415 volts from leg to leg, as Rob has described. It is actually 480 volts single phase. The 2 phases in such a situation are 180 degrees apart rather than 120 degrees. I have had such a supply in two different Victorian farms. I know it is 480 volts, as I have measured it. It has a centre tap, which supplies 240 volts at twice the current of a normal single phase supply.

I have only one 480 volt plug, in the workshop. Apart from that, the house is on one phase and the farm on the other.

I have what might be described as a "cocky's welder", a Transarc tradesman that puts out up to 230 amps. It has primary windings on its transformer for 240, 415 and 480 volts. I use it on 480 volts and it works much better than on 240.

480 volt electric motors are common. I have several. They are often designed to be used on either 240 or 480 volts.

If you double the voltage, you halve the current required for a given power.

You may well be able to draw 30 or 40 amps at 240 volts if the wiring and connectors are up to it. You might not draw quite that much in 480 volts.

Once you go above the standard 3 pin plugs for 10 and 15 amps there are several types of connectors. They all work. For my arc welder I use a standard 3 phase wall socket in the workshop, 3 phase extension leads and a 3 phase plug on the welder supply cable. It works fine.

How far away is the transformer? The closer the better, as there is less loss in a shorter cable run. Incidentally, the higher the voltage the lower the loss, as loss os proportional to current. That's why the big transmission lines are up to 500kV. Apparently in Siberia they use 1MV lines.

Roger
 
Roger that was very helpful.

the substation is probably within 2kms of the house but I'm told they would need to put a transformer in my street to meet my needs - hence the expense.

The take home message is that I lose out on the possibility of picking up cheap 3-phase equipment but the expense of buying more modern kit is more than offset by what it would cost to get 3 phase.

At present my welding requirements are modest. I do not need more than 15 amps for MIG and the next toy/s would be a quality compact TIG and/or a stick, both of which would be for auto work.

Thanks again

P
 
Roger Wilkinson said:
This is a bit of a grab bag of ideas, sorry.

The only real benefit of 3 phase power for someone with what I imagine to be your needs (serious hobbyist) is that you can buy old 3 phase equipment more cheaply than equivalent old 3 phase equipment. Single phase equipment will meet your needs. You don't need a big motor to drive a lathe. Mine has a 1 hp motor and it is quite enough. Similar story for a mill. Even my giant drill press and heavy grinder have only 2 hp motors, and I can't imagine you needing anything that big.

In many rural areas so-called 2 phase power is not 2 phases of a 3 phase supply with 415 volts from leg to leg, as Rob has described. It is actually 480 volts single phase. The 2 phases in such a situation are 180 degrees apart rather than 120 degrees. I have had such a supply in two different Victorian farms. I know it is 480 volts, as I have measured it. It has a centre tap, which supplies 240 volts at twice the current of a normal single phase supply.

I have only one 480 volt plug, in the workshop. Apart from that, the house is on one phase and the farm on the other.

I have what might be described as a "cocky's welder", a Transarc tradesman that puts out up to 230 amps. It has primary windings on its transformer for 240, 415 and 480 volts. I use it on 480 volts and it works much better than on 240.

480 volt electric motors are common. I have several. They are often designed to be used on either 240 or 480 volts.

If you double the voltage, you halve the current required for a given power.

You may well be able to draw 30 or 40 amps at 240 volts if the wiring and connectors are up to it. You might not draw quite that much in 480 volts.

Once you go above the standard 3 pin plugs for 10 and 15 amps there are several types of connectors. They all work. For my arc welder I use a standard 3 phase wall socket in the workshop, 3 phase extension leads and a 3 phase plug on the welder supply cable. It works fine.

How far away is the transformer? The closer the better, as there is less loss in a shorter cable run. Incidentally, the higher the voltage the lower the loss, as loss os proportional to current. That's why the big transmission lines are up to 500kV. Apparently in Siberia they use 1MV lines.

Roger
Click to expand...

Roger,

A minor correction. 480 volts does not exist as a Australian standard supply voltage.

The nominal phase to neutral voltage is 240v and nominal phase to phase voltage is 415v.

This is because of the sinusoidal angle relationship of the three phases, being 120 degrees separated.

Thus two phases provide 415v and not (2x240) which is the numeric, non vector addition, a misnoma.

For the record:

three phase voltage = (single phase voltage x root3)


cheers

Rob
 
robmac said:
Roger,

A minor correction. 480 volts does not exist as a Australian standard supply voltage.

The nominal phase to neutral voltage is 240v and nominal phase to phase voltage is 415v.

This is because of the sinusoidal angle relationship of the three phases, being 120 degrees separated.

Thus two phases provide 415v and not (2x240) which is the numeric, non vector addition, a misnoma.

For the record:

three phase voltage = (single phase voltage x root3)


cheers

Rob
Click to expand...

EDIT:

OK so there is a 480v phase to phase standard!
http://en.wikipedia.org/wiki/IEC_60309
It's certainly not used in Australia as a standard distribution system.

I vaguely recall a chap from WA with whom I worked with, saying certain isolated parts of WA used to have 265v single phase , which would approximate the 480 p-p standard.

So I live to learn.
 
You can also get 20Amp single phase welders.
 
robmac said:
Roger,

A minor correction. 480 volts does not exist as a Australian standard supply voltage.

The nominal phase to neutral voltage is 240v and nominal phase to phase voltage is 415v.

This is because of the sinusoidal angle relationship of the three phases, being 120 degrees separated.

Thus two phases provide 415v and not (2x240) which is the numeric, non vector addition, a misnoma.

For the record:

three phase voltage = (single phase voltage x root3)


cheers

Rob
Click to expand...

Hello Rob,

We have discussed this in the past, perhaps in the drill press thread (now deceased in the GAFC).

480v supply may not exist in theory in Victoria but it does exist in practice. I have 2 actives and a neutral coming from the transformer at the road to my meter box, and before the installation of a 3 phase smart meter I had a 2 phase spinning disc meter for the farm supply (it was labelled "2 phase 3 wire"). If you go out to the 480v power point on the workshop wall you will measure 480v across its active and neutral terminals. If you measure any of the 240v point points you will find 240v. I have measured it with my Fluke 87. You are welcome to call in with your own meter and see for yourself. You could look at the plates on the electric motors and read the labels saying 240/480v.

On second thoughts, don't call in so one of us can prove the other wrong, call in to say hello and kick a few tyres!

I doubt I have 2 legs of a 3 phase supply. I think my transformer has a single secondary winding that is 480v centre tapped. It is fed by 2 actives from a 3 phase 22kV line. Before I had the 480v point installed in the workshop, I had a 480v supply with one "phase" of 240v going to the house and the other to the farm, with 2 single phase 240v meters.

Roger
 
Great thread.!

Roger Wilkinson said:
Hello Rob,

.

On second thoughts, don't call in so one of us can prove the other wrong, call in to say hello and kick a few tyres!


Roger
Click to expand...

Roger and Rob.

Love your contributions and expertise on the subject of electrical power, between the both of you and the contribution of DoubleChevron, we all learn so much.:headbang:

I enjoy the way you guys think your way through the issues - as natures gentlemen do, and I totally like that comment above.

I hope to get your way sometime in the future and kick a tyre or two..:D

Regards

Ken:)
 
Roger Wilkinson said:
Hello Rob,

We have discussed this in the past, perhaps in the drill press thread (now deceased in the GAFC).

480v supply may not exist in theory in Victoria but it does exist in practice. I have 2 actives and a neutral coming from the transformer at the road to my meter box, and before the installation of a 3 phase smart meter I had a 2 phase spinning disc meter for the farm supply (it was labelled "2 phase 3 wire"). If you go out to the 480v power point on the workshop wall you will measure 480v across its active and neutral terminals. If you measure any of the 240v point points you will find 240v. I have measured it with my Fluke 87. You are welcome to call in with your own meter and see for yourself. You could look at the plates on the electric motors and read the labels saying 240/480v.

On second thoughts, don't call in so one of us can prove the other wrong, call in to say hello and kick a few tyres!

I doubt I have 2 legs of a 3 phase supply. I think my transformer has a single secondary winding that is 480v centre tapped. It is fed by 2 actives from a 3 phase 22kV line. Before I had the 480v point installed in the workshop, I had a 480v supply with one "phase" of 240v going to the house and the other to the farm, with 2 single phase 240v meters.

Roger
Click to expand...

OK you have a pole transformer. So it's a moot point whether is "supply".

But being installed by the supply company probably defines the 480v as supply. So I'm incorrect in my post/s above.

I'm City born and bred , so I have very little exposure to rural systems.

What you possibly have is a SWER (single wire earth return) to the transformer primary with a centre tapped secondary winding as you say. CT is neutral and the ends 2 x 240. So the windings are 180 degrees out of phase. So it's real two phase.

As distinct from two phases of a three phase system as with exfroggers situation.

As I said we live to learn... I'll do some more research...for my own interest.

edit:

I've added the pdf. Obviously SPAusnet, the infrastructure supplier, can provide 2x 240v as you have detailed. I assume they find this easier and less complex than providing a real three phase supply.

Very interesting....
 

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Last edited:
robmac said:
OK you have a pole transformer. So it's a moot point whether is "supply".

But being installed by the supply company probably defines the 480v as supply. So I'm incorrect in my post/s above.

I'm City born and bred , so I have very little exposure to rural systems.

What you possibly have is a SWER (single wire earth return) to the transformer primary with a centre tapped secondary winding as you say. CT is neutral and the ends 2 x 240. So the windings are 180 degrees out of phase. So it's real two phase.

As distinct from two phases of a three phase system as with exfroggers situation.

As I said we live to learn... I'll do some more research...for my own interest.

edit:

I've added the pdf. Obviously SPAusnet, the infrastructure supplier, can provide 2x 240v as you have detailed. I assume they find this easier and less complex than providing a real three phase supply.

Very interesting....
Click to expand...

No Rob, I don't have a pole transformer, and I don't have SWER. I'll try to be clearer about my setup. I have a transformer at the road, fed by 2 x 22kV actives going past. About 500m away from it, at a road junction, one of the 3 phases terminates. There are only 2 phases going past "my" transformer. My property is the only one fed by "my" transformer. It is about 400m from the transformer to the meter and fuse board on the front verandah of my house. Then there is distribution to the various sheds, each with its own sub-board.

On thinking a little more about it, does what I have constitute a "pole transformer" in your mind? I was thinking it doesn't, because the transformer is on the road and I have a long low voltage feed to my house. Maybe it does to you, if having a transfomer to yourself constitutes a "pole transformer".

I reckon exfrogger might find he has 480 volt single phase power with a centre tap, just as I have. This is commonly known in rural areas as "2 phase power". I have seen the same thing elsewhere. I had it on our previous farm. I think Shane had it in his former house on a suburban block in Ballarat.

As you say, I suspect it is a cheap and easy way to provide a greater power supply than single phase, without the expense of providing 3 phase. My arc welder appreciates it, although nowadays I tend to use my newly acquired multi-process inverter machine, which has a 240v supply but still seems to have plenty of grunt. (Does anyone want a grunty arc welding machine or 3?)

I'd be interested if you could find some official documentation of this setup. It's something I have asked almost every electrician and electrical engineer I have met for the past 30 years, and none of them have been able to explain it to me. It has taken these discussions with you on Aussiefrogs to start resolving it in my mind. But as we have seen, there are gaps, particularly around official documentation.

Roger
 
Kenfuego said:
I enjoy the way you guys think your way through the issues - as natures gentlemen do, and I totally like that comment above.

I hope to get your way sometime in the future and kick a tyre or two..:D
Click to expand...

Thanks Ken. I find it a pleasure to discuss things with Rob.

Aussiefrogger tyre kickers welcome.

Roger
 
Memory..

I'm straining my memory, back when I was knocking around Mallee Farms, most had 32 volt generators as a big advance from Kero lamps and pressure lamps, though I liked those.

When the SEC mains power was connected I seemed to think this was single? line in and earth return I can recall most had a round cylindrical Transformer that was pole mounted within the Farm proper and at the point that distribution was made to house and sheds.

I would have thought this woulf be described as a pole transformer but whether it is what you are both talking about I don't know, it did drive all sorts of electrical motors in and around the farm and machinery. Past that I didn't take any notice past the I flick a switch and the light comes on. twas enough for me at that time, wish I had learned more.

Probably wont help that much.

Roger Pm me with your latest most normal location etc. I'll see if we can call past one day.

Ken:)
 
Roger Wilkinson said:
N

I reckon exfrogger might find he has 480 volt single phase power with a centre tap, just as I have. This is commonly known in rural areas as "2 phase power". I have seen the same thing elsewhere.


Roger
Click to expand...

roger, isnt that what is depicted in the PDF in rob's post? on the one hand you are saying you dont have that, but in the quoted words you seem to be saying you do?
 
Kenfuego said:
When the SEC mains power was connected I seemed to think this was single? line in and earth return I can recall most had a round cylindrical Transformer that was pole mounted within the Farm proper and at the point that distribution was made to house and sheds.

I would have thought this woulf be described as a pole transformer but whether it is what you are both talking about I don't know, it did drive all sorts of electrical motors in and around the farm and machinery.
Click to expand...

Yes Ken, that's SWER. Signle Wire, Earth Return. Only one wire in. I think that's what Rob meant by "pole transformer" but I added the second paragraph when I realised I couldn't be sure what Rob meant. I hope Rob chips in again.

Roger
 
alexander said:
roger, isnt that what is depicted in the PDF in rob's post? on the one hand you are saying you dont have that, but in the quoted words you seem to be saying you do?
Click to expand...

Well, yes, alexander, the 480v centre tapped output I described is the same as in Rob's pdf. But the input is not. In the words you quoted I was talking only about the secondary, or output, of the transformer.

Single Wire Earth Return (SWER) transformer input has a single active wire coming in (SW). The only return path for the current is via the earth (ER). This is a bit dodgy, but does work in a rough sort of a way. There's some loss. It depends a lot on the quality of the earth, and each pole with a transformer mounted on it carries signs warning against indiscriminate digging around it, lest one disturb the various earth wires and stakes. But it is cheap to install and thus very common in rural areas. There is a lot of it between our farm and Warrnambool.

The transformer I have is supplied by 2 wires. Each is an active phase, and each acts as a return path for the other. This is a much more satisfactory approach than earth return, though more expensive.

Distribution to the transformer primaries in my setup is at 22kV (in Victoria, at least). I presume that is leg to leg (or delta), as there is no separate neutral wire. In contrast, SWER lines provide a lower voltage to the transformer, around 14kV I think. I don't know whether this is because a lower voltage is fed into it or because of inefficiencies in the earth return. Rob might know.

Roger
 
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