Fundamentals of Single-Phase AC Power Analysis
http://research.coe.drexel.edu/ece/power/wp-content/uploads/2014/04/1-phase-Power-Analysis.pdf
Fundamentals of Three-Phase AC Power Analysis
http://research.coe.drexel.edu/ece/power/wp-content/uploads/2014/04/3-phase-Power-Analysis.pdf