Transmission lines generally operate at 125 kV, 240 kV or 500 kV.
They range from a few kilometres long in urban situations to hundreds of kilometres in length for lines carrying power from distant generating plants. All of North America is interconnected. Read more
Every transmission (and distribution) system suffers line losses of between 6% and 8%. Whenever electricity passes along wires or through substations, it encounters resistance and loses some of its energy to heat.