Figure 5.25 a Simple equivalent circuit for ZnO material b Equivalent circuit for fast impulses. (Courtesy of IEEE working group 3.4.11: ‘Modelling of metal oxide surge arresters’, Transaction on Power Delivery, 1992, 7, (1), pp. 302–309, ฉ2003 IEEE) c Equivalent circuit to account for the dynamic conduction at highmagnitude fast impulses