Electrical networks of power transmission practically deals in the bulk transfer of electrical energy, from generating stations situated many kilometers away from the main consumption centers or the cities. For this reason the long distance transmission cables are of utmost necessity for effective power transfer, which in-evidently results in huge losses across the system. The Reliable electrical network is one that transports the energy with minimal power losses, losses corona effect represent one of causes that hinder reaching this performance in HV lines are either permanent mode or in the transient mode. In this paper we present the phenomenon of corona and its behavior in different climatic and atmospheric conditions such as rain, humidity, the dust, the sand, dry weather of the one part and over-voltages induced by strokes lightning. We deal in this paper, the influence of the corona under these different conditions on the power losses in the power lines and the proposal of a new model of three-phase line with transient corona.