Power lines run at huge voltages so less energy is lost as heat
Push electricity down a long wire and some of it warms the metal instead of reaching anyone. Raising the voltage lowers the current and cuts that waste, which is why transmission lines carry 110,000 volts or more. The transformer that made this possible was first built in 1881.
Early commercial power travelled at the same low voltage that lamps and machines used, and in 1882 there was no easy way to raise direct current voltage. So generators had to sit close to their customers. That changed after Lucien Gaulard and John Dixon Gibbs built a device they called a secondary generator in 1881, an early transformer. In 1884 a 34-kilometre alternating current line built for an electrical exhibition in Turin used their transformers, and in 1885 Rome gained the first commercial AC distribution system, lighting via dei Cerchi. That same year William Stanley Jr. produced the first practical transformer of its kind, and with George Westinghouse's backing he demonstrated an AC lighting system in 1886.
Most lines today are overhead, strung from bare aluminium alloy strands, sometimes with a steel core, because aluminium is far lighter and cheaper than copper. The surrounding air is their insulation, so they need clearances; heat makes them sag, and winds of just 43 kilometres an hour can swing them close enough to arc. Underground cables avoid weather and eyesores but cost much more to lay, take longer to repair, and for AC lose usefulness beyond about 80 kilometres.
For very long runs, and for undersea links, high-voltage direct current is more efficient. North America has four big synchronised grids, called interconnections: Western, Eastern, Quebec and Texas, while a single grid spans most of continental Europe.
Supply must match demand from moment to moment. When demand outruns generation, plants and lines can trip off automatically, and a local failure can cascade. The US Northeast suffered blackouts in 1965, 1977 and 2003. Linking networks across regions and even continents provides backup routes and reduces that risk.
Source: Electric power transmission
