Author Topic: What do Americans mean by 'single phase'?  (Read 673 times)

Offline DavidA

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What do Americans mean by 'single phase'?
« on: September 16, 2019, 06:06:10 PM »
Hi all.

I'm a bit puzzled.

When we in the UK talk of single phase we refer to one leg of the three phase system generated by the power supplier, and a neutral leg. which is, if I remember correctly, connected to the centre of the three phase 'star' at the generator.

So we have 240Volt (nominal) between each phase and the neutral line.  And 415 volt (nominal) between any two phases.

Unless specially requested (and paid for) we get use of just one leg and the neutral.

I have been running my 415 Volt three phase motors via a 240 to 415 transformer, then using capacitors to make the ghost phase.  It works, but not very satisfactory as the pony motor soon gets too warm.

However, I recently watched the video...



By sbirdranch 'Building a phase convertor (parts 1 to 3)'

I began considering checking if my motors are 240/415 Volt. And if so maybe I can run them as 240Volt. Saving the transformer and making the purchase of run capacitors a bit less expensive.

But then I got to wondering about the American supply.

I think they have three phase 120 Volt to their houses, and they obtain the 240 Volt by utilising two of the phases.

They don't appear to use the neutral line in this set-up as this would not give 240 Volt required.  I'm not altogether clear on this point.

I someone could take a few minutes and look at the link, then get back abs tell me whether or not I can use our normal single phase system in the same way, I would be very grateful.

(also, does this require the motor to be connected in Delta ?)

Dave,

Offline efrench

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Re: What do Americans mean by 'single phase'?
« Reply #1 on: September 16, 2019, 08:51:50 PM »
It's a phase most teenagers and young adults go through before finding a mate. :Doh:

Offline WeldingRod

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Re: What do Americans mean by 'single phase'?
« Reply #2 on: September 16, 2019, 09:39:44 PM »
We Americans have the thrill of getting access to a single leg feeding a center tapped 240 vac transformer, with the center tap grounded.  Like you, three phase service for houses is "bought and paid" dearly for, assuming it gets anywhere near your house.  Most of the runs down the street are a single leg!
Our small loads get 120 vac, and the big stuff goes across the full transformer output of 240.

Sent from my SAMSUNG-SM-G891A using Tapatalk


Offline djc

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Re: What do Americans mean by 'single phase'?
« Reply #3 on: September 17, 2019, 02:31:06 AM »
...I began considering checking if my motors are 240/415 Volt. And if so maybe I can run them as 240Volt....

...tell me whether or not I can use our normal single phase system in the same way, I would be very grateful...

To answer the second part first, many urban areas in UK have a three phase cable running down the street and each home is fed alternately off one of the phases (i.e. house 1, phase 1; house 2, phase 2; house 3, phase 3; house 4, phase 1). So if you are friendly with the neighbours on both sides, you could borrow a phase of each of them and have 415v phase to phase. This is undoubtedly illegal and unsafe, but theoretically possible.

For the motors, start with the data plate. If it says 240/415v or has symbols resembling a Y and a triangle on it, then it should be easy. Three phase motors have three coils inside, so six wire ends. To give maximum flexibility of connection, all six ends need to be user-accessible. In most modern single speed motors this is the case, but in older ones, three of the ends are connected together (star point) and buried more or less deeply inside the guts of the motor.  If you have the time and inclination, you can dig out the star point, separate and insulate the three wires and bring them out for use.  In some motors, this is not too difficult; in others, it is all but impossible. The only way to find out is to open up the motor and have a look.

Offline mattinker

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Re: What do Americans mean by 'single phase'?
« Reply #4 on: September 17, 2019, 03:28:29 AM »
So we have 240Volt (nominal) between each phase and the neutral line.  And 415 volt (nominal) between any two phases.

Yes

Unless specially requested (and paid for) we get use of just one leg and the neutral.



But then I got to wondering about the American supply.

I think they have three phase 120 Volt to their houses, and they obtain the 240 Volt by utilising two of the phases.

They have 220 volt three phase, one phase and neutral providing the 110 volt out put.

You can't get 415volts out of the UK system from a single phase supply without a transformer.


If you have 240/415 motors, you can wire the "Delta" run the on 240 three phase which you can obtain through a phase converter or, alternatively, a VFD.

It is worth noting that for small sizes, VFDs are now very cheap, probably less than the price of your condensers! I recently bought one, postage included, for a 3/4 hp motor for £42!!!

Regards, Matthew.




Offline Muzzerboy

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Re: What do Americans mean by 'single phase'?
« Reply #5 on: September 17, 2019, 06:53:17 AM »
I moved my workshop over to Canada for 4 years (along with my family!) and simply ran my machines across the 240V supply which is used for heavy loads like the clothes drier and cooker. The only functional difference was that any on-line motors ran 20% faster (60Hz vs 50Hz) but if you are using VFDs, that issue doesn't arise anyway.

From a safety point of view, the neutral connection is generally earthed at the utility transformer, whether in N America or elsewhere. However, if you connect your equipment across 2 phases or across the 120-0-120 connection, both your "live" and "neutral" equipment connections are now live. Not a big issue but you might consider fitting a fuse on what used to be the "neutral" line in the equipment. Typically, only the "live" connection is fused in single phase equipment. Otherwise, you will be relying on the main circuit breaker, which may be fine, as I said.

BTW, 120-0-120 is not "two phase", it's single phase with an earthed centre tap neutral.

Offline allanchrister

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Re: What do Americans mean by 'single phase'?
« Reply #6 on: September 17, 2019, 09:20:28 AM »
Same question but the opposite.. Next year I will be moving to Germany and I have a number of 110v machines. Anyone know if I can get 110v supply from a German domestic house supply as usual voltage is 220/240v.? Enough to run a small mill and lathe.

Offline Pete.

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Re: What do Americans mean by 'single phase'?
« Reply #7 on: September 17, 2019, 11:00:57 AM »
Alan, the simplest way is to just get a yellow portable site  transformer from the UK. These are readily available and easy to use.

Offline Muzzerboy

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Offline vintageandclassicrepairs

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Re: What do Americans mean by 'single phase'?
« Reply #9 on: September 17, 2019, 04:25:37 PM »
Hi All,
Quote
Next year I will be moving to Germany and I have a number of 110v machines. Anyone know if I can get 110v supply from a German domestic house supply as usual voltage is 220/240v.? Enough to run a small mill and lathe.

Allen,
It really depends on the type of motor fitted and if they are suitable to work on 50Hz
Some motors are marked 50/60Hz and these will work OK but run at a lower speed than in USA
Other 60HZ motors will overheat on 50Hz and need a reduced voltage supply
USA 3 phase 220v 60Hz motors need the voltage reduced to 208v when run on a 50Hz system

I had reason to visit a companies premises here in Ireland where a lot of their equipment had been brought over from USA, Special transformers were installed to run those machines

John

Offline allanchrister

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Re: What do Americans mean by 'single phase'?
« Reply #10 on: September 18, 2019, 09:24:22 AM »
Thanks guys, Iíve run the machines from 220v before through a step down transformer but wondered if 110v was available from a German household panel. I have transformers so Iíll take them with me

Offline DavidA

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Re: What do Americans mean by 'single phase'?
« Reply #11 on: September 18, 2019, 03:39:54 PM »
Thanks for the replies.

Mathew,

At the moment I do use a 220 to 415 transformer to bring the Voltage up

I was just considering the option of only using 220 Volt on the motors that are 220/415 Volt.

I may go for the VFD option if they are now so cheap. As I can get at both ends of the coils in the motors I have looked at I will be able to wire them in Delta.

If anyone looked at the video I linked to, what did you think of his method of 'tuning' the capacitors to equal out the voltages ?

Dave.

Offline Muzzerboy

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Re: What do Americans mean by 'single phase'?
« Reply #12 on: September 19, 2019, 09:07:26 AM »
Haven't bothered watching the whole thing but being a smartass, I think I can see what is going on. With this scheme, you need a capacitor size that "matches" the load current. The trouble is that capacitors have fixed capacitance, yet the load current varies according to the load on the machine. That's why a single ie fixed capacitor value struggles to both start up a motor and get it to run well under all conditions. You can switch in different values but that's where it becomes difficult.

I've got a suds pump that works fine with a single "motor start" cap providing the connection to the third phase - but that's a simple, fixed load and isn't very critical. Rotary phase converters are a better solution for driving motor loads, as the motor is acting rather like a transformer. VFDs are even better for driving motors from single phase, with the added bonus of speed control. It's horses for courses, cost vs benefit etc.

Offline GordonL

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Re: What do Americans mean by 'single phase'?
« Reply #13 on: September 19, 2019, 12:15:43 PM »
I have built phase converters using a relay which drops out the start capacitors once the motor is started and then uses run capacitors once the motor is started. This is the idea.

http://www.k3pgp.org/3phconv.htm

Offline DavidA

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Re: What do Americans mean by 'single phase'?
« Reply #14 on: September 19, 2019, 04:09:46 PM »
Thanks for the extra info.

I did wonder about his connecting one leg via a capacitor to the neutral, if the neutral is connected to Earth in his supply.

Would this not trip his Earth Leakage Contact Breaker ?

I know that If I try the 'old school' method of checking for a live by putting a lamp bulb from Live to Earth, I am quickly left in the dark.

Offline Muzzerboy

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Re: What do Americans mean by 'single phase'?
« Reply #15 on: September 20, 2019, 09:06:08 AM »
A ground fault detector (GFI or GFCI in N America or RCD in Europe) checks to see if the sum of the L and N currents is zero. It should be zero - if it isn't, it means that some current is finding an alternative path from L (or N) back to ground. So yes, if you connect a bulb from live to ground, this will be testing that the GFCI / RCD is working ok. Modern "split circuit" consumer units have 2 separately protected circuits so you can connect the lights to one and your loads to another. Then, when you trip a power circuit you aren't left in the dark. Very clever.

If you connect a load from L to N, this should not trip the circuit. However, this won't do a whole lot to create a third phase. The only reason for fitting a capacitor like that would be to adjust (improve) the power factor when you have a large inductive load. It doesn't help the load to work better but it can mean you don't pay so much for your power. I'm not sure the guy really knew what he was doing but as I said, I couldn't be arsed to watch the whole thing.

Offline ddmckee54

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Re: What do Americans mean by 'single phase'?
« Reply #16 on: September 20, 2019, 01:10:16 PM »
Muzzerboy:

He was probably using the capacitor to help shift the phase on that leg of the circuit.  I don't know how much it would shift it, it's been WAY too many years since I did any calculations like that, makes my head hurt just thinking about it.

I did something similar about 25-30 years ago to test a PLC interface for some 3 phase power monitoring equipment when I only had single phase available in the shop.  I used the inductance of a 1000' spool of wire to shift the signal to the monitoring equipment.

Don
Too many irons, not enough fire.

Offline DavidA

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Re: What do Americans mean by 'single phase'?
« Reply #17 on: September 21, 2019, 03:55:58 PM »
The bit about connecting a capacitor from a phase to ground/neutral was towards the end of the video.

Anyway, any current leakage from either the lighting or the power circuits trips my whole system. So I probably won't be trying that.

Dave.