Tavner, Peter; Li Ran, ; Penman, Jim; Sedding, Howard: 'Condition Monitoring of Rotating Electrical Machines' (Energy Engineering, 2008) DOI: 
IET Digital Library, https://digital-library.theiet.org/;jsessionid=aon49t1sl9dhr.x-iet-live-01content/books/po/pbpo056e