Why do high-volt­age power lines crackle and hiss?

Focus-Science and Technology - - Q & A - RICHARD LIND­LEY,

It’s pri­mar­ily the ef­fect of the high volt­age on the air sur­round­ing the ca­ble. Air is nor­mally a very poor con­duc­tor of elec­tric­ity. But if a suf­fi­ciently high volt­age is ap­plied across a small dis­tance, elec­trons from the air mol­e­cules are stripped off and start to form a cur­rent. This in turn causes in­tense heat­ing of the air – re­sult­ing in crackle and hiss. It’s most com­mon dur­ing damp weather, when the air be­comes a bet­ter elec­tri­cal con­duc­tor.

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