Today the web offers quite a lot of general information about electrical power engineering, that I use gratefully. Below are some interesting websites.
Wikipedia offers not only in English, but also in the Dutch language interesting information about electrical power engineering. Start at the category Power Engineering. Or search on subject, for example current transformer or Resistance thermometer.
Schneider Electric offers a lot of Cahiers Techniques in English and French. You can download these PDF documents from the website.
Siemens offers a lot of Tech Topics in English at their US website.
Alstom offers the Network Protection & Automation Guide, that you can download on request. This book is the successor of the well-known book Protective Relays Application Guide (PRAG) of GEC in Stafford (UK).
Basler Electric offers interesting Technical Papers about excitation systems (voltage regulators) and protection relays. After registration you can download these PDF documents.
Universities offer free bieden gratis subject material via the internet. This is named OpenCourseWare (OCW). The Massachusetts Institute of Technology started in 2002 (ocw.mit.edu) and the University of Technology in Delft in 2007 (ocw.tudelft.nl).