Answer / rajesh sahu

We know that Corona loss is dirctly proportional to frefuency(F+25).
We know that DC voltage is free from frequency(f).
In dc f=0, so corona loss proportional to 25(less frquency gives rise to less loss in DC as compare to AC)

Answer / akki

AC voltages are associated with skin effect and thus,
current flows effectively very close to the surface of the
cables. Therefore, resistance offered increases.
Since AC resistance is greater than DC resistance and corona
discharge is favorable in higher conductivity, therefore the
dc voltage to achieve corona is lower than the ac voltage
needed to produce corona

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