3-Phase Terminology:

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rattus

Senior Member
Correct me if I am wrong:

"Line Voltage" means the voltage between any pair of live wires in a 3-phase system.

"Phase Voltage" means the voltage between any live wire and neutral even if the neutral does not exist. One can always calculate the equivalent 4-wire wye voltages from the line voltages.

"Phase" should not be used to describe the two live wires in a 240/120 single phase system.

I know I will muddy the water here, but maybe we will come out knowing a bit more than we did.
 

jtester

Senior Member
Location
Las Cruces N.M.
Re: 3-Phase Terminology:

As an electrical engineer, I have been taught to look at it a bit differently. We differentiate line and phase voltage depending on the ystem.

In a wye system Vline=1.73XVphase
Iline=Iphase

In a delta system Vline=Vphase
Iline=1.732XIphase

Lots of people will look at it differently, this is how I have been taught.

Jim T
 

Ed MacLaren

Senior Member
Re: 3-Phase Terminology:

I would say that you are both correct. :)

The voltage across each load is another way of looking at the term "phase voltage".
Ed

3ph7.gif
 

john m. caloggero

Senior Member
Re: 3-Phase Terminology:

The 3-phase terminology I learned in engineering class is as follows:
LINE VOLTAGE is the voltage across any two phases at the output terminals of the generator or transformer.
PHASE VOLTAGE is the voltage across the individual coil winding. For example in a 3-phase wye connected transformer, the voltage across the individual coil winding is 120 volts. The vector sum of the coils connected in series 120 degrees out of phase results in a line voltage of 1.73 x 120 =208 volts. In a delta connected system, the line voltage and the phase voltage are the same. However, the currents in each coil winding is added vectorally so if you have 173 amps of line current, you will have a phase current of 100 amps in each of the coil windings.
 

rattus

Senior Member
Re: 3-Phase Terminology:

OK now, I dug a little deeper in my AC circuits book, and they seem to be saying that Vphase is the voltage across the xfrmr secondaries however they are wired. Vline is the voltage between pairs of live wires, and Iline is the current in the individual wires. They just didn't say it in so many words.
 

charlie b

Moderator
Staff member
Location
Lockport, IL
Occupation
Retired Electrical Engineer
Re: 3-Phase Terminology:

Originally posted by rattus: Correct me if I am wrong: "Phase Voltage" means the voltage between any live wire and neutral even if the neutral does not exist.
That sentence makes no sense, and it is not correct. If there is no neutral, then you can not measure voltage between another point and the neutral. The term ?phase voltage? means the voltage from one side of a secondary winding to its other side. For a delta-connected secondary, that would be the same as the line-to-line voltage. For a wye-connected secondary, the phase voltage is measured from a line to the neutral.
 

rattus

Senior Member
Re: 3-Phase Terminology:

Charlie, I asked for a correction, and I got it. I see now that my definition of phase voltage is correct only for the wye configuration. I am also saying that, on paper or in your mind, you can convert a delta problem to a wye problem.

I just didn't dust off my ancient textbooks completely!
 
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