question on three phase??

[sparkysam]

Hi there all, I'm an apprentice working as a maintenance electrician, deal with domestic day to day, wanted to ask a quick question on three phase, a voltage indicator measures the potential difference between conductors, 230v between line and earth single phase, and on three phase 230 between each phase and earth, but why do we get 400v between phases, I would've thought 0v between phases as there's no potential difference, on a learning curve at the moment and would be great full for you answers , cheers

 

[Sidewinder]

Due to the phase angle, think about the 3 phase system and the phase shift.

 

[Evans Electric]

Each line is 1/3 of a cycle out of phase with each other and reverses its direction each half cycle .

Look at a drawing of a star wound generator , say, forget that stuff I've just put , imagine three seperate outputs with 400v between and the star point is zero ,neutral .

The potential difference as you say, is not 0v but 400 v

If you're doing housing work, you'll find 3 phase in the street , first house conected to red /neutral oops sorry , L1 /N next house connected to L2 /N third house to L3 &N then back to L1 .

You could find 3 Ph in a large house , but usually only at the meter then it would divide into S/ph .

 

[ProDave]

Just to add a bit to the above, the way it works out, is if say one phase is right at it's extreme positive voltage, the next phase will be somewhere part way through it's negative cycle. Hence why the phase to phase voltage is higher than phase to neutral (or star point)

A quick google finds this picture Phase diagram

That shows the voltage of the 3 phases over time. At any instant, it's clear that the voltage between phases is higher than each phase individually.

 

[sparkysam]

Thanks for that, that's really helped with understanding it, researched it too, vL = 1.732(square root of 3) x 230 = 398. cheers guys

Thanks guys, that's really helped, I've researched into it and I'm getting my head around it cheers

 

[Andy™]

Hi there all, I'm an apprentice working as a maintenance electrician, deal with domestic day to day, wanted to ask a quick question on three phase, a voltage indicator measures the potential difference between conductors, 230v between line and earth single phase, and on three phase 230 between each phase and earth, but why do we get 400v between phases, I would've thought 0v between phases as there's no potential difference, on a learning curve at the moment and would be great full for you answers , cheers

just to complicate things, you can also get split phase where you have 2 phases 180 degress apart, with 460v between them....