I guess you are trying to do homework with these questions.

think about what corona is and what corona loss might be dependent upon. Wouldnt you think that the losses would be dependent upon the ionizability of the insulator? So relative humidity, temp, barometric pressure would affect corona losses. Also the distance between the conductors will have a lot to do with it.

I believe that the idea of homework is to make you more self reliant. The internet and the bibliography in your various texts should be your first choice. The answers on these forums are frequently full of S**T.

Have a look at

http://large.stanford.edu/courses/2010/ph240/harting1/ and

http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19750024094_1975024094.pdf

http://en.wikipedia.org/wiki/Electric_power_transmission

Please read the link below you will get your answers.

http://en.wikipedia.org/wiki/Corona_discharge