back flashover voltage on transmission tower of 275 kv extra high voltage line (case study: galang-binjai)

Overvoltage at the insulator terminal caused by a lightning strike can occur in two ways, i.e., a direct lightning strike on the phase line and ground wire. the insulator can be exposed to the phenomenon of back flashover (bfo) if the terminal voltage of the insulator is higher than its insulator critical voltage the lightning current characteristics are distinguished by the maximum current and the steepness. differences in the characteristics in this study are identified as international electrical commission (iec) and conseil international des grands reseaux electriques (cigre) impulse waveform standards. the footing-tower grounding system comes in different configurations, such as horizontal, vertical, and grid. alternative transient program (atp) software was used for simulating lightning strikes on ground wire and phase lines. the results exhibit that the highest critical voltage of the insulators on the footing tower through grid grounding when the surge current strikes ground wire (3308kv – 3395 kv), with the magnitude of the lightning current ranging from (48 ka – 3395 ka). for lightning direct stroke on the phase line, the critical voltage on vertical grounding is highest on (2938 kv -3021 kv).  the surge current flow footing-tower is highest on the grid. the currents magnitude flow in footing tower were influenced by impedance of grounding.