Converting 3 phase to 110/120v nightmare 4

[theboosh]

Hi, our company uses a machine powered by US 3 phase mains/ generator (200...240VAC). In the UK we can power an auxilliary device that goes with the machine from the 400V, as the 3 phase is able to give a leg of normal mains power( with one live and neutral?)(240V). Is there a way to do this in the US? I cant seem to see a way that it can be spurred off because there is no neutral...if not is there some kind of transfromer that I can use?
Any help would be really appreciated..

 

[Barry1961]

Many VFD's will run off single phase power. How big is the motor?

Barry1961

 

[theboosh]

Hi there,
We use 5kw...is that OK...sorry I don't really know about VFD's!

 

[EEJaime]

Hello,

If you are referring to a UK voltage of 347Y/600V, you are dealing with a 3-phase, 4-wire secondary which already has a phase to neutral voltage available. If correspondingly you have a US standard 200V, (either 208v or 240v), you probably have either a 240V, 3-phase, 3-wire, delta connected transformer with no neutral-or a 208Y/120V,3ph/4w system which has both three phase and 120V single phase power available. If you have the 240V delta system you have a couple of options. Either a 240V, delta primary to 208Y/120V wye connected secondary transformer which would give you the neutral point for your auxilliary devices, (check thier ratings). Or a single phase transformer connected to one phase of the three phase transformer to provide a 120/240V,1ph/3w output, for which you would need to establish a ground point for the neutral. Others may have alternative approaches, but you should speak with someone there in the UK about local alternatives.

 

[waross]

Hi theboosh
I have adjusted voltages, and converted from 50Hz. to 60 Hz. and vice versa.
What voltages have you available, and is a netral available?
What are the voltage and current ratings of the motor or machine that you intend to connect?
Does the machine need a neutral?

Voltage adjustment with "off the shelf" auto transformers often does not give the exact voltage, you have to "fudge" some of the motor voltage tolerance.
Frequency re-rating, same situation, you have to fudge a little of the voltage tolerance.
I'd check that the total fudging isn't too much.

The easiest voltage conversion is an open delta, auto-transformer connection. It takes two transformers per
motor or group of motors, but doesn’t have a neutral.
The current rating required is the percentage of voltage change. For single phase, if you have to change the voltage by 10% then the rating of the auto-transformer will be 10% of the load rating.
The three phase arithmatic is just as easy.
I can give you the connections and ratings, and hopefully some-one local can help us with code compliance.

Can someone tell us what voltages of dry type lighting transformers are available in the UK?

The ones that I most often use in North America are;
1> Primary voltage. 240:480, Secondary voltage 120:240
2> Primary voltage 240:480 Secondary voltage 12:24
3> 0.75 KVA, 1 KVA, 2KVA, 5KVA

 

[jghrist]

Usually in the USA, 120V single phase lighting power is obtained from a 240 V delta supply by center-tapping one phase.

 

[LionelHutz]

I'm a little confused. You want to power a 240V auxiliary device from a 208...240V mains, right? Connect it between 2 phases and just fuse both phases.

If you get a 240:240 transformer (basically an isolation transformer) then you can create your 240V and neutral to power your aux devices.

 

[theboosh]

thank you all for your replies!
I want to power a 110v device from the 208...240v 3 phase. pretty certain i have the 240V, 3-phase, 3-wire, delta connected transformer with no neutral. Or a least that is what the machine requires.
What kind of cost would a delta primary to 208Y/120V wye connected secondary transformer be...? I'm thinking it sounds expensive.
This is a feature we use in the UK, because its free. But I'm thinking if there is cost to this we can power the 110v small device from the generator that accompanies it and lose this feature...

 

[ccjersey]

5kw on 120V would require some pretty big conductors. If you use 240 line-neutral in England, why not use the same 208-240V equipment connected line-line here instead of the 120v?

 

[theboosh]

Well, the larger machine takes the three phase 208...240V but the other equipment is required to be powered from 'normal' us mains, it is only a small piece of kit, similar to a glue gun, they just like it to have the facility to be powered from a point from the machines electrical feed, this is easy in England to get 240V off the three phase but in the US its not so easy to get the 110v from the 208..240 3Phase. Hope that makes sense...

 

[CJCPE]

You should be able to use a single phase 208/240:120v step down transformer. You may need a dual voltage primary if the voltage range acceptable to the small load is not wide enough to accept 104 to 120v or whatever corresponds to the range actually experienced on the primary side. Connecting a single phase transformer to two lines of the 3-phase supply will unbalance the load a little, but it would be equivalent to the unbalance you get when you connect a single phase aux load in the UK.

 

[ScottyUK]

Just a small point for EEJaime:

347Y/600V isn't a normal UK supply voltage. Our LV mains distribution is 240/415V, or supposedly 230/400V if you listen to the European Union. There is the odd bit of 650V single phase used by the rail industry, but they have their own legacy standards. Isn't 600V a North American (Canadian?) voltage?

Most UK systems are either 3-wire 3-phase (no neutral) or 4-wire three phase (with neutral). Obviously the latter has scope for supplying single phase loads from one phase and the neutral. For flexibility I would suggest use of a transformer between two phases for the auxiliary load, which then allows the unit to be used on either supply type.


----------------------------------

Your body might be a temple. Mine is an amusement park...

 

[waross]

Hi theboosh.
I am still trying to figure out what country you are in.
The solution to your problem is probably quite easy and quite economical.

What voltage and frequency does your machine require?

What country are you in and what voltages do you have available?

If you are in the US, you probably have the voltages you need. If you are in the UK, I can help you select a small inexpensive transformer, but I need to know just a little bit more.
FYI
My experience is Canadian. We share many standards with the US, including three phase transformer systems.
Three phase Delta at 240 Volts is probably quite rare, and would only be used industrially.
Residential and commercial loads have so many 120 volt devices connected that three phase Delta without a 120/240 tap would be unlikely.
Three phase Delta at 480 Volts would be more likely, But these systems were popular so long ago, that the standard voltager then was 440 Volts.

Standard transformer connections and voltages.
1> 120/240 Vots single phase. One transformer.
Common for residential and small comercial.

2> 124/240/208 Volts three phase. Open Delta. Two
transformers. 120/240 single phase, 240 volt three phase. 208 volt "Wild leg" This voltage is not used.
Fairly common in rural areas for irrigation pumps.
Used anywhere the load is predominantly single phase, but a small capacity of three phase is needed for a special machine.

3> Full delta. Same voltages as above, but three transformers.
Rare. no application residentially or commercially. May be used industrially.
4> Probably the most widely used in terms of installed KVA
is the 120?208 Volt Wye connection with three transformers.
Almost universal for large shopping malls, office buildings,
hotels, and any large installation that has a lot of 120 volt utilization equipment.

 

[theboosh]

Hi all!
I'm in the US. basically the machine needs 3 phase 200..240v 50Hz (no neutral) for the US to power it but we need to somehow get 110v from it to power the small glue gun.
In the UK we used 400V 3L neutral and earth @60Hz , so it was ok to get a 240v leg off it, to power standard equipment
With us having no neutral here in the US, and believe the feed to be delta, it seems impossible to go from the 200...240 3 phase, and take a live/ hot wire(s) to create our normal 110v.

In a nutshell, after the electrical circuit has powered the machine at 200..240v 3 phase, turn it in to standard us mains voltage of 110v.

But thank you all so far for your really helpful responses, I think I maybe at least understand it a bit more now..!

 

[waross]

Hi theboosh
I wonder if we are a little confused over the term "Neutral"?
I am assuming that your background is UK.
I had a misunderstanding some years ago with a UK engineer over what constituted a neutral connection It took us a few interchanges to get on the same page. There was a slight difference in expectations as to what exactly was a neutral. Fortunately he was patient with me.
It is EXTREMELY RARE to have a 240 volt panel with no neutral.
Remember, in the US, we connect 120 volt loads from a single pole breaker to the neutral bus bar.
There should be 5 large cables coming into your panel. The three heaviest will be the three phase conductors. Color code Red, Black, Blue, or all Black. These cables connect to the three bus bars that feed the breakers.

The fourth cable may be the same size or smaller. Color code White.
This will connect to the Neutral bus. Any wires connected to this bus will be the return legs from single phase 120 volt loads. To connect your 120 volt load, One lead will go to a circuit breaker, and the other leg will connect to this bus.

The fifth wire will be the Ground cable. It may be smaller again. Color code Green. This cable connects to the ground bus to which all your ground wires should be connected.

If you are in the US, and you have any receptacles in your building, you probable have 120 volts.
Like wise, if you have any incandesent lanps on the cieling, you have 120 volts.

It is possible that you have an old three phase delta panel with no neutral if you are in a very old industrial use building. Possibly 50 years old or more. A three phase ungrounded panel may have been used for safety concerns. This would probably be for three phase loads only. There are probably other panels in the building for the 120 volt lighting loads.
There are other possibilities, such as no receptacles and 240 volt lighting, but code concerns would probably rule this out.

If this is the case, you may be able to run a line to a 120/240 volt or 120/208 Volt panel to power your small load. you may even be able to use an extension cord.

If your panel is definately 240 volts only, and power from a 120/240 volt panel is not an option for any reason, tell us the current and voltage rating of your small device and we will be able to point you in the direction of a small dry type transformer to get the voltage you need.

It would help us to help you if you can take your voltmeter to the panel and measure the voltages. As well as breaker to breaker, it is important to measure breaker to ground voltages from at least three breakers in a row, (On some panels, with half inch breakers, six breakers in a row.) or from the main cable connections, and if you do find a neutral buss, measure breakers to neutral bus.

Even with an ungrounded Delta you should be able to measure voltages to ground because of capacitive effects and leakage. If your panel is indeed ungrounded, there should be 3 or 6 ground detector lights above it..

 

[EEJaime]

ScottyUK,

You are correct in that the voltage I stated is Canadian in origin. I made another of those ill fated jumps to a conclusion which you pointed out is incorrect. I guess I am of an age which still considers Canada as part of the UK and would hence expect to drive on the left side of the road up north.

Yes 600V is still a North American Standard, used mostly in rail and industrial applications. It seems to be on it's way out' much as most 240V systems. Your suggestion of the transformer on two phases is similar to my suggestion for the 240V, 3ph/3wire system with no neutral.

We have the same nomenclature irregularities in the US. We still see specifications for 440V. systems, 460V systems, 480V systems, 200V, 208V, 210V, 115/230V,230V, 240V, etc..., the base standards now recognized by most utilities are the 208Y/120V, 3phase, 4-wire; 120/240V, 1-ph,3-wire; 240V,3-ph,4-wire,[center tapped-high leg, being eliminated as facilies are updated]; 480Y/277V,3ph,4w and the 600V, 3ph,3w system. Many of the odd labels are antiquated remnants of various regional standards which still have footholds in some manufacturing circles, but which will eventually be phased out. Many motors we see are still labeled at 230/460V.

 

[theboosh]

Think I'm confused over the whole thing! Background is UK, yes, I've been forced into looking into this electrical sitution we have, its not really my field of expertise at all.
Its a modern building and the 'disconnect box' is brand new.
OK, there are 4 cables coming into the box, 3 live/ hot wires which are black and one earth/gnd.
Measuring the voltage, I get 208v measuring between 2 live wires, I get 120 by connecting a live and the earth...I think this could be good?

waross, thank you for your patience!

 

[jghrist]

To serve the 120 volt single phase auxiliary load, you will need to run an insulated grounded (neutral) conductor to the load. The grounded conductor would be bonded to the service ground at the service equipment (probably the box you are talking about).

 

[ccjersey]

Hooray! Just hit the jackpot there boosh!

You got what you need to run your 120V glue gun. Any phase wire and a neutral conductor, not a ground or using the frame as a neutral though. Just need to make sure the electricians pull the neutral to the machine and not just the 3 phases and ground wire.

 

[waross]

I concur with ccjersey.
The neutral is at ground potential in North America.
If you check closely you will find that the Neutral bus, which you are calling the ground is actually insulated from the panel. If it is the main panel, there will be a screw or jumper conecting the panel box to the neutral bus. Only one such connection is allowed per building. In a sub panel, there is no connection between The Neutral and ground even though they are both the same potential. If there is provision for a ground wire on your glue gun, it must be connected back to the ground bus or screws in the panel with a green wire. The return for your 120 volt glue gun should be a white wire and connect to the neutral bar. There may be another bus bar in the back of the panel, or there may be one or more rows of screws taped into the back of the panel. These are your ground connections. What is the make and model of the panel?
Yours.