3-phase calculations shortcut

[ban-all-sheds]

No - I am not branching out into commercial/industrial...

I need to explain to someone why 3-phase volt-drop figures are (SQRT(3))/2 of the single phase ones. (I hope I'm right that that is what they are..... )

I'm sure that with time I could work it out (well, sort of maybe sure), or find a website showing the calculations, but don't have that time right now.

Can anybody help me, either with the calculations, or pointing me at a web resource?

 

[plugwash]

mmm 3 phase

you'll have to tell me what you are and aren't changing between the single phase calcs and the 3 phase ones before your statement makes any sense.

for a given conductor size and conductor current and assuming balanced load a 240/415V three phase system will have half the P-N voltage drop of a 240V single ended single phase system as there is no neutral current.

 

[ban-all-sheds]

Pick any multicore table in Appendix 4, and compare the VD for 2-core single phase and 3- / 4- core three phase....

 

[ban-all-sheds]

for a given conductor size and conductor current and assuming balanced load a 240/415V three phase system will have half the P-N voltage drop of a 240V single ended single phase system as there is no neutral current.

Which of course is how we get to SQRT(3)/2 - if there was a neutral current the VD would be the single-phase figure x 1.732..., but with no neutral current it becomes S-P x 0.866....

Doh.

 

[plugwash]

ahh thier figures are based on the drop in the phase-phase voltage

makes sense now.