High Voltage Engineering

A 400 kV line shown in figure below is effectively grounded which is protected by L.A. with PR = 3. The transformer has its protection ratio (TPR) = 1.25 with $Z_{c} = 350$ Ω. Determine BIL of Tr. Also find the maximum distance between transformer and lightning arrester so that the insulation coordination is properly met. [IMAGE: Figure from the original paper, showing the 400 kV effectively grounded line protected by a lightning arrester and the transformer.]