Highest voltage for equipment Um KV 24 36 52 72.5 100 123 145 170 245 300 362 420 550 Rated frequency Hz 50/60 50/60 50/60 50/60 50/60 50/60 50/60 50/60 50/60 50/60 50/60 50/60 50/60 Dry power frequency withstand voltage 1 minute kV 55 77 105 155 205 255 305 355 505 505 560 750 870 Lightning impulse(BlL) kV 125 170 250 325 450 550 650 750 1050 1050 1175 1550 1800