winnie
Senior Member
- Location
- Springfield, MA, USA
- Occupation
- Electric motor research
Smart $ said:Umm, the formula is for a 120? 3? 4W voltage system. I believe it to be impossible to have three equal currents at those angles on 4W mwbc of such a system.
It would be difficult, but not impossible, to set up loads that give the currents and phase angles that Rattus suggested.
I could, for example, set up 3 line to neutral loads. One is resistive, one has a significant capacitive component (leading power factor), and the third has significant inductive component (lagging power factor). Put enough effort into being intentionally unbalanced, and you could get all three legs nearly in phase.
In reality, with reasonable loading, one expects similar power factor on each of the legs on a feeder. The phase angles will all be approximately (but not exactly) 120 degrees apart, and thus an equation that depends upon 120 degree phase angles will be a good approximation.
However, consider the following situation: A panel that feeds only resistive loads, say heaters in a process. You have 30A of line-neutral loads on phase A, 10A of line-neutral loads on phase B, 10A of line-neutral loads on phase C, and 20A of line-line loads from phase B to phase C. What is the current on the feeder neutral?
-Jon