Cables VS transmission lines

It is known, folks, that electrical energy is transmitted and distributed between electrical equipment and supplies, either by ground cables or overhead lines, and each part has its uses according to the conditions of the extension and the surrounding environment.

The fundamental difference between cables and overhead lines is that the conductors used in overhead lines are exposed and not insulated, and they are installed on towers to maintain fixed separation distances between the conductors and each other and between the conductor and the ground. However, in cables, the conductors used are insulated with layers of insulation, and are extended either By direct burial in the ground, through cable trays, or through conduits.

• How to choose between ground cables and overhead transmission lines??????

Of course, dear engineers, the differentiation between them and the selection between them is not done according to one criterion, but rather according to several basic criteria, the most important of which are:

• 1- The cost of the conductor, and the conductor is the basic part that carries the electric current. It is either aluminum or copper, and most of the conductors in cables and lines are aluminum, but!!!!!!!!!!!..for the same power, the conductor used in the lines is less expensive than The conductor used in cables, given that the Current Carrying Capacity of lines is much higher than in cables…why is it so??…Because the resistance in lines is less than in cables, and cables have a very large distance and a smaller cross-sectional area, which corresponds to a higher resistance and a lower current. …Therefore, the transmission line conductor is smaller in size and less expensive than in cables.
• 2- The cost of the insulator: We notice that the transmission lines on the towers contain only two insulators, an insulator with the body of the tower made of porcelain, and an air insulator between the conductors and each other, because there are no mechanical or electrical stresses like cables. Cables have higher insulators and are more expensive than lines, and we note that the cable It usually consists of eight layers, from the beginning of the conductor to the last PVC insulation, passing through the insulation of the conductor, the insulation curtains, the filling, the metallic sheath, the inner jacket, and the concrete block. All of this is because the insulation is exposed to cracks, mechanical stresses, conditions of the soil itself, and conditions for loading, and all of this costs. Calculated for the insulator, which is many times the cost of the transmission line insulation.

• 3- Installation cost: Of course, it is known that installing or burying a cable is much more difficult and more expensive than hanging a transmission line. The cable is like a person buried in the ground. All means of complete comfort must be available, including a layer of sand, and a burial depth of no less than a meter…which leads to Ultimately, the cost increases.

We add to the above, that the cables are excluded from being used for long distances, due to the value of the capacitance of the cable, which affects the transmitted power, because it consumes charging currents, which depend on the operating voltage, frequency, and capacitance, which leads to the loss of half of the capacity in the form of charging currents…