Corona

Reduce the fair weather surface voltage gradient on all energized electrodes (inclucing conductor) to below the corona inception level of the surrounding air at the elevation of the transmission line.

There are actually 3 types of AC corona that occur at different gradients or voltage stresses. At sea level and ambient temperature of 25°C (standard temperature and pressure), negative polarity glow corona appears at approximately 20 kV rms/cm. It appears visually on the ends of cotters, projections and sharp corners as a light continuous glow and does not generate significant RIV/TVI (radio influence voltage/television interference), nor contribute significantly to corona loss. At a gradient of approximately 25 kV rms/cm, negative polarity brush corona appears. It gets its name from the appearance of the corona discharges; the ends of which look like the bristles of a bristle brush. It normally appears on the negative half-cycle and also does not generate significant or objectionable RIV/TVI. It makes an audible crackling sound. At approximately 30 kV rms/cm positive polarity plume corona appears. It's much louder and generates visible plumes on the positive half-cycle and does generate significant RIV/TVI and resistive power loss.

In rain storms virtually all energized electrodes and conductors are noisy and generate significant RIV/TVI, audible noise and resistive power loss.

Many are under the impression that the dielectric strength of air is greater under dry conditions. That is not true. In fact, the dielectric strength of air increases with increased moisture up to the dewpoint when moisture begins to condense on the surface of insulators and other components of the line.

You reduce the inception voltage by increasing the effective radius of the conductor. That is bigger diameter or bundle configuration.

By increasing the spacing between the conductors....

Conductor Space comes under proximity effect know?