Ultra High Voltage is defined as voltages of 1,000 kV alternating current, or higher, and 800kV direct current, or higher, and it is needed for two main reasons. The first is to deliver large quantities of power over very long distances with very little loss of power (higher voltage means lower current on the transmission line and therefore lower loss). The second is to deliver large quantities of power to cities without having a proliferation of transmission lines. If you can deliver lots more power with just one line, you don’t have to build more lines and the resulting overall impact is reduced. In places where demand is growing but room for transmission lines is limited, such as Tokyo in Japan, this is critical because it means only one power line corridor is needed, not several.