J. Lewis Blackburn 
Symmetrical Components for Power Systems Engineering [PDF ebook] 

Emphasizing a practical conception of system unbalances, basic circuits, and calculations, this essential reference/text presents the foundations of symmetrical components with a review of per unit (percent), phasors, and polarity—keeping the mathematics as simple as possible throughout. According to IEEE Electrical Insulation Magazine, this book "…provides students and practicing engineers with a fundamental understanding of the method of symmetrical components and its applications in three-phase electrical systems. . .A useful feature of this book. . .is the incorporation of numerous examples in the text and 30 pages of problems."