Q7Power System - I

Corona formation on transmission line conductors is affected by: (1) atmospheric conditions — corona is more severe in humid, foggy or rainy weather and at lower air density (higher altitude, higher temperature), since ionization threshold decreases; (2) conductor surface condition — rough, dirty, scratched or damaged conductor surfaces have higher local field concentration and lower corona onset voltage than smooth, clean conductors; (3) conductor size (radius) — larger-diameter conductors have lower surface voltage gradient for the same line voltage, reducing corona; (4) spacing between conductors — greater spacing reduces the electric field intensity at the conductor surface, raising the disruptive critical voltage; (5) supply voltage — corona loss increases roughly with the square of the excess of operating voltage over the critical disruptive voltage; and (6) line voltage frequency — corona loss increases with the supply frequency.