 The transformers step up the voltage from 16 kV to 275 kV for transmission . Six oil @-@ filled cables carry the electric current up a cable shaft to a point in front of the dam , and from there it is carried on pylons to Dalmally 8 kilometres ( 5 @.@ 0 mi ) to the east . The staircase in the cable shaft has 1 @,@ 420 steps , making it the tallest in Britain . 
