Living in this modern world is truly wonderful, especially as there is just so much information out there. Now there is no excuse for saying "I could not find what I needed"! On this page are just a few resources open to anyone wanting to further study this rather dynamic subject. In alphabetical order..
This link takes you to another section of the website dedicated to supporting a range of products that I have come to appreciate. Application notes for Fluke, Reliable Power Meters, Enetics, and other PQ instruments can be found under the appropriate "Advanced Operating" sections.
Their application sheets, specifically those pertaining to Power Quality, are well worth a look. Although specifically product focused, they are generic enough to assist the starter to PQ. I would almost advocate a read of these before even attempting to read this book!
These can be located on the navigation bar on the left under "Application Notes".
Tutorials and Standards for the Power Quality Industry; Short, simple power quality tutorials for engineers - they're free, they're short, and they're a great way to get started. Once you've gone through the tutorials, you may want to look a little closer at these guys - they actually make bad power!