WRT a 'star' (4 wire) system, the textbook
Further Electrical & Electronic Principles states that 3-phase power can be found by taking simultaneous measurements with just 2 watt-meters. Further:
(a) Access to star point
not required (b) Power for either balanced
or un-balanced loads is obtained
Calling the 3 phases r,b,g the picture in the book shows we measure
Vrb and I
r, Vyb and I
y That is, our common measurement node for voltage is the 'b' phase.
However, the proof then seems to assume a balanced load
Ir + Iy = -Ib
I looked this up online and found the following
https://www.newtons4th.com/wp-content/uploads/2010/03/APP014-3-Phase-2-Wattmeter-Explained.pdfNow this document states
Note: In a 4 wire system the Star Point/Neutral will be used as the Volts Lo common point
This would mean access to the star-point
is required.
For a 4-wire 'star' 3-phase system with an un-balanced load and using the two-wattmeter method:
- Can I derive total load power?
- Is access to the Nuetral (Star) terminal needed?