1. Generally, overhead lines do not need to be insulated because the insulation distance and safety distance are enough. If the insulation is added, the cost is particularly high. There is not only the cost of the insulation layer, but also the cost of supporting facilities. For example, when the pole is bearing, the diameter must be increased. In order to ensure the safety height to the ground, the strength and height need to be increased;

2. The bare wire is conducive to heat dissipation. If the insulation layer is added, the thickness will reach tens of centimeters, increasing the power consumption;

3. The high-voltage line adopts the safety height to the ground to ensure safety, and uses air insulation.