Aylett, P.D.: 'The energy-integral criterion of transient stability limits of power systems', Proceedings of the IEE - Part C: Monographs, 1958, 105, (8), p. 527-536, DOI: 10.1049/pi-c.1958.0070
IET Digital Library, https://digital-library.theiet.org/;jsessionid=2n4cufai02upk.x-iet-live-01content/journals/10.1049/pi-c.1958.0070