Across a whole continent, grid generators turn in lockstep
On a synchronous electrical grid, every generator's alternating current rises and falls at almost the same instant, across areas as large as continental Europe. North American grids swing 60 times a second and European ones 50. Tying so much together saves money, but a problem in one corner can ripple everywhere.
A grid links power stations, substations that raise or lower voltage, long-distance transmission lines and local distribution wiring into one system. Nearly all grids use three-phase alternating current, which carries far more power per wire than a single phase because conductors are shared, and three-phase machines run more efficiently. Voltage may be transformed several times between generator and customer. Even so, high-voltage AC lines lose around 1 to 4 percent of their power per hundred miles, and direct current links can halve that.
North America has four big synchronised zones, called interconnections. Joining neighbours lets them pool generating plants and demand, share reserves, and buy energy from whichever sources are cheapest and most efficient. Zones running at the same frequency can be merged directly; others can trade power through links that do not require syncing. The European Union set targets for each national grid's cross-border links to equal 10 percent of its generating capacity by 2020 and 15 percent by 2030. Planners also sketch supergrids, moving huge quantities of electricity over great distances to smooth out swings in wind and solar output.
At the other end of the scale sits the microgrid, a local network usually tied into the wider grid but able to cut loose and run alone during outages, a trick known as islanding. Using lower voltages and nearby generators, microgrids can be tougher and cheaper for remote places, and ideally a community produces all the energy it consumes.
Many people remain unconnected. In 2016 about 1.4 billion people had no grid electricity; by 2017 the figure was around 840 million, mostly in Africa, down from 1.2 billion in 2010. As grids add computer control, protecting them from cyberattack has become a growing concern.
Source: Electrical grid
