Independent engineering articles explaining electrical systems and single line diagrams
https://electrical-engineering-portal.com
Engineering blog covering power system modelling and intelligent single line diagrams
https://etap.com/blog
Reference library of electrical symbols used in single line diagrams
https://symbols.radicasoftware.com/229/single-line-symbols
Transmission network power flow diagram of the Great Britain electricity system
https://www.nationalgrid.com/sites/default/files/documents/37785-ETYS%202014%20Appendix%20C%20-%20Power%20Flow%20Diagram.pdf