corner grounding a single phase transformer

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kinnirish

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I have an Italian packaging machine i am installing in a facility with 480 volt delta incoming power. The machine is has a 415 volt, three phase, 50 hz configuration for all the hardware. I am pulling the original 400 v/50 hz control transformer due to the need for 230 volt single phase demand for inverters, power supplies, and heaters. If the existing control transformer is supplied with 480 volts, my output will be 277v which is too high. question is: can I "corner ground" a 480v to 240 v single phase delta transformer to achieve the 240v to neutral voltage needed, or should i purchase a delta/wye transformer to achieve this. I don't wish to purchase another transformer if I can make this work. Any ideas? your help would be greatly appreciated.
 

jim dungar

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question is: can I "corner ground" a 480v to 240 v single phase delta transformer to achieve the 240v to neutral voltage needed.

Your question is not clear.
Do you have a three phase transformer or a single phase transformer?

Does your equipment need 240V single phase with a neutral , or just 2 wires?

But yes, you can take a two winding single phase transformer (480-240 1Ph 2W) and ground one leg of the output so that you get 240V L-G.
 

Smart $

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Ohio
I am confused (probably in the same manner as Jim)...

I can see changing out a control transformer that was originally 400V-PRI/230V-SEC, 50Hz to one that is 480V-PRI/240V-SEC, 60Hz... but how do you plan to operate the entire machine if it is configured, and remains configured for 415V 3? 4W 50Hz...???

Seems to me you need to set up three (3) 480V-PRI/240V-SEC 1? transformers as a delta primary, wye secondary bank to power the entire machine, and leave the control transformer as it is. Get transformers with overvoltage taps (i.e. taps that reduce secondary voltage). You should be able to get pretty close to 400Y/230V 3? 4W 60Hz. You also need to determine what will happen when you power 50Hz components with 60Hz power!!!

PS: 415V wye is equivalent to 240 L-N; 400V wye (or 398V) corresponds with 230V. Which is it 415 or 400?
 
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kinnirish

Member
Your question is not clear.
Do you have a three phase transformer or a single phase transformer?

Does your equipment need 240V single phase with a neutral , or just 2 wires?

But yes, you can take a two winding single phase transformer (480-240 1Ph 2W) and ground one leg of the output so that you get 240V L-G.

I have a single phase transformer(480-240/120) and require 240 volts, phase to neutral. Sounds like that will work. Thanks!
 

jim dungar

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I have a single phase transformer(480-240/120) and require 240 volts, phase to neutral.
If the transformer is connected as a 2-wire secondary, you may connect one of the line/hot wires to ground, but technically it is not a neutral.
 

Besoeker

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Location
UK
If the transformer is connected as a 2-wire secondary, you may connect one of the line/hot wires to ground, but technically it is not a neutral.
How would you define neutral?
Here, it is very common to use a control voltage of 110Vac in (industrial) electrical panels. This is usually derived from a 400V primary (line to line) to a 110V secondary single phase transformer with the winding marked 110V and 0V. We consider these to be live and neutral respectively and earth (ground) the 0V.
Not neutral?
And if not, why not?
Just asking.
 

jim dungar

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A neutral conductor is a common reference point which usually has equal potential to multiple other conductors. Almost all neutral points are connected to ground/earth so most electricians fall into the habit of calling all grounded, or 0V, reference points 'neutrals'.

There are systems that have 0V conductors which are not neutrals. For example, a corner grounded delta a multi-tapped transformer with simultaneous 24V and 120V load connections, and a 2-wire transformer output with one grounded conductor.
 

Besoeker

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A neutral conductor is a common reference point which usually has equal potential to multiple other conductors.
I have a single phase supply into my house.
There are three conductors, live, neutral, and earth. The plugs (plug ins) and wall sockets have three terminals labeled L, N, and E.
Here's one I installed:

WallSocket01.jpg



The neutral is a reference to just one other conductor. Live.
It's still a neutral, isn't it?
 

jim dungar

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I have a single phase supply into my house.
There are three conductors, live, neutral, and earth. The plugs (plug ins) and wall sockets have three terminals labeled L, N, and E.


The neutral is a reference to just one other conductor. Live.
It's still a neutral, isn't it?
It depends on the source of the supply.
If the source is a 400Y/230 transformer then yes the common conductor is a neutral, even if the circuit is only 2 conductors + ground.
However, if the source is a single voltage source (i.e. a single transformer winding) no true neutral point exists.

Only as recently as 2009, has our NEC finally defined the terms neutral conductor and neutral point.
 

Besoeker

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Location
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However, if the source is a single voltage source (i.e. a single transformer winding) no true neutral point exists.
Rural locations sometimes have a pole mounted single phase transformer.
It was like that where I grew up.
The service was still three conductors. live, neutral and earth.
Why would the neutral not be a "true" neutral in that case?
 

jim dungar

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Rural locations sometimes have a pole mounted single phase transformer.
It was like that where I grew up.
The service was still three conductors. live, neutral and earth.
Why would the neutral not be a "true" neutral in that case?
What is it "neutral" to?

What makes it different than your "live" conductor?
 

Besoeker

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Location
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What is it "neutral" to?

What makes it different than your "live" conductor?
The fact that it is at or about earth potential. Obviously the live isn't. Touch that then the live and you will be in no doubt as to which is live - no I'm not suggesting that anyone does.
Just trying to illustrate the point.

It's certainly called neutral at the distribution board.
Plugs and sockets label it as neutral.
 

jim dungar

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The fact that it is at or about earth potential. Obviously the live isn't.
With a 2-wire output, it is at earth potential simply because it is connected to earth.

Disconnect your neutral from earth, now connect your live to earth, all voltages to ground have not changed.

Take the neutral from a wye source and disconnect it from earth, now connect one of the live conductors to earth, all voltages to ground have changed.

In the NEC the word "neutral" means the center point of a wye, or the midpoint of a 3-wire system.
A FPN (which I believe is based on IEEE) says: At the neutral point of the system, the vectorial sum of the nominal voltages from all other phases within the system that utilize the neutral, with respect to the neutral point is zero potential. Evidently, the NEC definition of a "neutral conductor", the conductor connected to the neutral point of a system, is based on the IEC.
 

Besoeker

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With a 2-wire output, it is at earth potential simply because it is connected to earth.

Disconnect your neutral from earth, now connect your live to earth, all voltages to ground have not changed.
The live is live only because it is not connected to earth. The neutral is neutral because it is. Doesn't matter which you pick.
Take the neutral from a wye source and disconnect it from earth, now connect one of the live conductors to earth, all voltages to ground have changed.
What makes the star point neutral? Maybe because it is connected to earth as a rule?
And, if you connect a live conductor from a Y source to earth, is it really still live?
Is the star point still neutral? Potential to earth in such an arrangement would make it potentially shocking.
We don't generally have an expectation that a neutral conductor would be at a shocking potential.
 

don_resqcapt19

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Under the NEC definitions the grounded conductor of a two wire system is not a neutral.
Neutral Conductor. The conductor connected to the neutral point of a system that is intended to carry current under normal conditions.
Neutral Point. The common point on a wye-connection in a polyphase system or midpoint on a single-phase, 3-wire system, or midpoint of a single-phase portion of a 3-phase delta system, or a midpoint of a 3-wire, direct-current system.
 

jim dungar

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What makes the star point neutral? Maybe because it is connected to earth as a rule?
No, connection to earth does not define a neutral.

It is neutral because the vector sum of the "live" conductors is zero at that point.
 

Besoeker

Senior Member
Location
UK
No, connection to earth does not define a neutral.

It is neutral because the vector sum of the "live" conductors is zero at that point.

Thanks Jim and Don. Appreciate

Part of the definition of a neutral point by Don:
midpoint on a single-phase, 3-wire system,
In UK, a single-phase supply to a building is always 2-wire for the current carrying conductors and designated designated live and neutral.
There are no three wire single phase systems

From Jim:
It is neutral because the vector sum of the "live" conductors is zero at that point.
If you take the vector sum of phase to neutral voltages on a three-phase system, yes it will be zero. The same on the midpoint of a single phase system where the two lives are 180 deg apart. Again zero for the vector sum of the voltages.
But if, as in UK, you have just a single-ended single-phase voltage, it is a non-zero sum.
But one is designated neutral.
Different countries. Different countries, different systems and I'm sure part of this is historical.
I have learned a lot from this forum on a number of topics.
Including the differences between the LV distribution systems between UK and USA.
You have 480, 277, 240, 208, 120, and possibly others.
For me, as a simple Brit, that seems just a bit overly complex or maybe unnecessarily complex.

In UK, LV distribution is 400V three phase, 230V single phase (phase to neutral of 400V) or sometimes just single-phase 230V.
With very few exceptions, residential service is single-phase 230V. All domestic equipment is rated to run on 230V. From phone chargers to washing machines and water heaters. And everything in between. A lost neutral from a centre-tapped 120-0-120 possibly resulting in overvoltage for some circuits isn't a problem we encounter.

As I mentioned earlier, the differences may be historical. And you work with what you have. The LV electrical distribution infrastructure for developed countries has been in place for very many years. Changing them this late in the game isn't an option.

But I like simple.
 
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