# Voltage for Single Phase Transformer

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#### rongyuer_2001

##### Member
Experts,

I'm a Chinese electric engineer, recently I work on a electric software which is only face to US, I'm not very clear with some US standard, so here I want to ask a very basic question,
If a transformer is a single phase one, its primary Voltage is defined as 12470Y/7200V, what does 7200V mean?
IMO, only 3-phase transformer has this kind of Voltage definition, e.g if a 3-phase transformer's voltage is 12470Y/7200V, that means its phase-to-phase voltage is 12470V, and phase-to-neutral voltage is 7200V.....
But, what does these 2 value mean when it is a single phase one.....?

Any explanation will be appreciated!!

#### Smart \$

##### Esteemed Member
Experts,

I'm a Chinese electric engineer, recently I work on a electric software which is only face to US, I'm not very clear with some US standard, so here I want to ask a very basic question,
If a transformer is a single phase one, its primary Voltage is defined as 12470Y/7200V, what does 7200V mean?
IMO, only 3-phase transformer has this kind of Voltage definition, e.g if a 3-phase transformer's voltage is 12470Y/7200V, that means its phase-to-phase voltage is 12470V, and phase-to-neutral voltage is 7200V.....
But, what does these 2 value mean when it is a single phase one.....?

Any explanation will be appreciated!!
Can't explain. I'm of the same opinion as yours.

Perhaps a programming error in the software. What is the software application's name? Maybe someone here uses the same software and can check their version.

#### kwired

##### Electron manager
Experts,

I'm a Chinese electric engineer, recently I work on a electric software which is only face to US, I'm not very clear with some US standard, so here I want to ask a very basic question,
If a transformer is a single phase one, its primary Voltage is defined as 12470Y/7200V, what does 7200V mean?
IMO, only 3-phase transformer has this kind of Voltage definition, e.g if a 3-phase transformer's voltage is 12470Y/7200V, that means its phase-to-phase voltage is 12470V, and phase-to-neutral voltage is 7200V.....
But, what does these 2 value mean when it is a single phase one.....?

Any explanation will be appreciated!!
I really don't know but will throw out a suggestion that it might mean it must be connected from one phase to ground and not phase to phase.

#### CTCOX

##### Member
A probable guess

A probable guess

I would imagine that the single phase transformer in reference is a double bushing transformer, meaning, there are two primary bushings. If you use two of the 3 primary phases (12,470V ph to ph) one per bushing, you will get the secondary voltage on the name plate -OR- if you decide to Ground one of the primary bushings (utilizing the system Neutral) and wire the other primary to one phase (7,200V Ph to Neutral) you will get the secondary voltage on the name plate.

12,470V is the reference of primary voltage phase to phase. 7,200 is the reference of each phase to neutral. Much like 480/277V. 480V divided by 3 is 160 times the square root of three (1.73) = 277V -OR- 12,470 divided by 3 is 4156.7 times square root of three (1.73) = ... Tada!

A U.S. standard term for single phase is 120/240V 3 wire, that does not necessarily mean the Power company uses only one primary phase to serve the "single phase" service.
Hope that helps....

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#### kwired

##### Electron manager
I would imagine that the single phase transformer in reference is a double bushing transformer, meaning, there are two primary bushings. If you use two of the 3 primary phases (12,470V ph to ph) one per bushing, you will get the secondary voltage on the name plate -OR- if you decide to Ground one of the primary bushings (utilizing the system Neutral) and wire the other primary to one phase (7,200V Ph to Neutral) you will get the secondary voltage on the name plate.

12,470V is the reference of primary voltage phase to phase. 7,200 is the reference of each phase to neutral. Much like 480/277V. 480V divided by 3 is 160 times the square root of three (1.73) = 277V -OR- 12,470 divided by 3 is 4156.7 times square root of three (1.73) = ... Tada!

A U.S. standard term for single phase is 120/240V 3 wire, that does not necessarily mean the Power company uses only one primary phase to serve the "single phase" service.
Hope that helps....
Not saying it is impossible but I would guess a 12.47/7.2 kV dual voltage is not too common. Most dual voltage single phase distribution transformers I am aware of are 4.16/7.2 kV, but I am not a POCO guy so maybe I don't really know what is common.

#### CTCOX

##### Member
Not saying it is impossible but I would guess a 12.47/7.2 kV dual voltage is not too common. Most dual voltage single phase distribution transformers I am aware of are 4.16/7.2 kV, but I am not a POCO guy so maybe I don't really know what is common.
It is completely dependent on the POCO's system voltage. Here in the Quad Cities (Moline, IL and Davenport, IA area) we have a 13,200/7,620V primary system, same company in the Des Moines area utilizes the 12,470/7,200V primary system. The voltage that you are referencing seems uncommon to me, but I guess it would determine which area you are operating out of and just goes to show how important it is to check the name plate on the transformers. A simple fat finger of a digit or two on a stock code while ordering a transformer for a project could easily result in the wrong transformer delivered.

#### kwired

##### Electron manager
It is completely dependent on the POCO's system voltage. Here in the Quad Cities (Moline, IL and Davenport, IA area) we have a 13,200/7,620V primary system, same company in the Des Moines area utilizes the 12,470/7,200V primary system. The voltage that you are referencing seems uncommon to me, but I guess it would determine which area you are operating out of and just goes to show how important it is to check the name plate on the transformers. A simple fat finger of a digit or two on a stock code while ordering a transformer for a project could easily result in the wrong transformer delivered.
I had that wrong, the ones I see the most are 2.4/7.2 kV.

#### CTCOX

##### Member
I had that wrong, the ones I see the most are 2.4/7.2 kV.
If I had to guess, I would assume that you primarily work in an urban area. The 2.4 kV system is good for short distances and is usually used by you "city folk". If we had a 6 mile primary tap at 2.4kV in a rural setting, the grain bins would have the corn dry by planting season.

#### weressl

##### Esteemed Member
Experts,

I'm a Chinese electric engineer, recently I work on a electric software which is only face to US, I'm not very clear with some US standard, so here I want to ask a very basic question,
If a transformer is a single phase one, its primary Voltage is defined as 12470Y/7200V, what does 7200V mean?
IMO, only 3-phase transformer has this kind of Voltage definition, e.g if a 3-phase transformer's voltage is 12470Y/7200V, that means its phase-to-phase voltage is 12470V, and phase-to-neutral voltage is 7200V.....
But, what does these 2 value mean when it is a single phase one.....?

Any explanation will be appreciated!!
It simply means that it is a reconnectable winding set for either voltage.

 G201-10-1 Single-Phase Overhead-type Distribution Transformer Specification

#### kwired

##### Electron manager
If I had to guess, I would assume that you primarily work in an urban area. The 2.4 kV system is good for short distances and is usually used by you "city folk". If we had a 6 mile primary tap at 2.4kV in a rural setting, the grain bins would have the corn dry by planting season.
Smaller towns usually have 2400/4160. Some have been using dual voltage transformers in anticipation that they will eventually be converted to 7200/12470. Most everything else is 7200/12470.

#### mivey

##### Senior Member
If a transformer is a single phase one, its primary Voltage is defined as 12470Y/7200V, what does 7200V mean?
The 7200 is the winding voltage.

IMO, only 3-phase transformer has this kind of Voltage definition, e.g if a 3-phase transformer's voltage is 12470Y/7200V, that means its phase-to-phase voltage is 12470V, and phase-to-neutral voltage is 7200V.....
But, what does these 2 value mean when it is a single phase one.....?
The other indicates that it can be used in a 12.47 system as long as you have the neutral (thus giving the 7200 volts for the winding).

#### mivey

##### Senior Member
Not saying it is impossible but I would guess a 12.47/7.2 kV dual voltage is not too common. Most dual voltage single phase distribution transformers I am aware of are 4.16/7.2 kV, but I am not a POCO guy so maybe I don't really know what is common.
It is not dual rated for 12.47x7.2 kV. The 4 kV and 12 kV dual voltage transformers are common on old systems that are planning for a conversion (we also use 12 kV and 25 kV dual voltage transformers, etc)

#### mivey

##### Senior Member
It simply means that it is a reconnectable winding set for either voltage.
Nope. It has to do with the transformer being suitable for use on a 12 kV system as long as we have the neutral. 7200 is the only primary voltage rating for this transformer.

#### weressl

##### Esteemed Member
Nope. It has to do with the transformer being suitable for use on a 12 kV system as long as we have the neutral. 7200 is the only primary voltage rating for this transformer.
Did you check the attached links?

#### mivey

##### Senior Member
Did you check the attached links?
No. Just speaking from experience and my feeble memory.
Perhaps I have overlooked something? But since you insist...

#### Hv&Lv

##### Senior Member
I'm with mivey here...
We use 12470Y/7200 / 24940Y/14400 dual voltage pots. All this means is that they will work on a Y system, with one tap 7200 L-G, and the other 14,400 L-G.

I thought you engineers like to use the L-L voltages in a system to keep them straight. If I say 7200 volt system, is that delta or Y? By writing 12470Y/7200, there should be no confusion. BTW, this is what our straight pots have on them...

#### rongyuer_2001

##### Member
If I had to guess, I would assume that you primarily work in an urban area. The 2.4 kV system is good for short distances and is usually used by you "city folk". If we had a 6 mile primary tap at 2.4kV in a rural setting, the grain bins would have the corn dry by planting season.
Yes, We also has 24940Y/14400v voltage setting.
The standard we are using is "UNITED STATES DEPARTMENT OF AGRICULTURE---Rural Utilities Service", so maybe 24940V is used for urban and 12470 is used for rural, is it right?

#### rongyuer_2001

##### Member
Can't explain. I'm of the same opinion as yours.

Perhaps a programming error in the software. What is the software application's name? Maybe someone here uses the same software and can check their version.
product name is AUD (Autodesk Utility Design)
The standard we are using is "UNITED STATES DEPARTMENT OF AGRICULTURE---Rural Utilities Service", so maybe 24940V is used for urban and 12470 is used for rural, is it right?

#### rongyuer_2001

##### Member
I'm with mivey here...
We use 12470Y/7200 / 24940Y/14400 dual voltage pots. All this means is that they will work on a Y system, with one tap 7200 L-G, and the other 14,400 L-G.

I thought you engineers like to use the L-L voltages in a system to keep them straight. If I say 7200 volt system, is that delta or Y? By writing 12470Y/7200, there should be no confusion. BTW, this is what our straight pots have on them...