'Mathematical background to protection algorithms' (Energy Engineering, 1995), 'Digital Protection for Power Systems', Chap. 2, pp. 7-38, DOI: 10.1049/PBPO015E_ch2 IET Digital Library, https://digital-library.theiet.org/;jsessionid=227c6cp28m52v.x-iet-live-01content/books/10.1049/pbpo015e_ch2