Question:

Is there a difference in electricity losses from overhead and underground power lines?

Answer:

For a given transit capacity (same voltage), in theory a buried cable has fewer losses than an overhead line, at least for low and medium voltages. However, it is difficult to give figures because, as the specialists from the EDF distribution department explain, this varies as a function of numerous parameters (cable type and crosssection, voltage, etc.). Buried cables have their own drawbacks, such as the production of "reactive" energy, which is not directly usable. Due to the "resistance" of the conducting wires, line losses are proportionate to current squared (Ohm’s law). This is why current is kept as low as possible, which increases voltage proportionately: by up to 400,000 volts for extra high voltages (EHV). Unfortunately, in the case of EHV, buried cables result in the highest loss in transported energy. To overcome this, substations have to be built every 50 to 80 km for 90,000-volt lines, every 25 to 30 km for 225,000-volt lines and every 15 to 20 km for 400,000-volt lines. In that case, the cost would be 10 to 12 times greater than for overhead lines.