Mains electricity



Mains electricity (as it is known in the UK and some parts of Canada; US terms include utility power, grid power, domestic power and wall power; in much of Canada it is known as hydro) is the general-purpose alternating-current (AC) electric power supply. It is the form of electrical power that is delivered to homes and businesses, and it is the form of electrical power that consumers use when they plug domestic appliances, televisions and electric lamps into wall outlets.
In the UK, mains electric power is generally referred to as "the mains". More than half of power in Canada is hydroelectricity, and mains electricity is often referred to there as "hydro". This is also reflected in names of current and historical electricity monopolies such as Hydro-Quebec, BC Hydro, Manitoba Hydro, Newfoundland and Labrador Hydro, and Hydro One.
All these parameters vary among regions. The voltages are generally in the range 100240 V (always expressed as root-mean-square voltage). The two commonly used frequencies are 50 Hz and 60 Hz. Single-phase or three-phase power is most commonly used today, although two-phase systems were used early in the 20th century. Foreign enclaves, such as large industrial plants or overseas military bases, may have a different standard voltage or frequency from the surrounding areas. Some city areas may use standards different from that of the surrounding countryside (e.g. in Libya). Regions in an effective state of anarchy may have no central electrical authority, with electric power provided by incompatible private sources.
Electronic appliances (such as those in the televisions, computer and related equipment categories above, representing 9% of the total), typically use an AC to DC converter or AC adapter to power the device. This is often capable of operation over the approximate range of 100 V to 250 V and at 50 Hz to 60 Hz. The other categories are typically AC applications and usually have much more restricted input ranges. A study by the Building Research Establishment in the UK states that "The existing 230 V system is well suited to the future of electricity whether through design or Darwinian processes. Any current perceived weakness is generally a result of cost reduction and market forces rather than any fundamental technical difficulties. Questions as to whether there are alternatives to the existing 230 V AC system are often overshadowed by legacy issues, the future smart agenda and cost in all but specific situations. Where opportunities do exist they are often for specific parts of the overall load and often small parts in terms of total demand.
The world's first public electricity supply was a water wheel driven system constructed in the small English town of Godalming in 1881. It was an alternating current (AC) system using a Siemens alternator supplying power for both street lights and consumers at two voltages, 250 V for arc lamps, and 40 V for incandescent lamps.
In 1899, the Berliner Elektrizitats-Werke (BEW), a Berlin electrical utility, decided to greatly increase its distribution capacity by switching to 220 V nominal distribution, taking advantage of the higher voltage capability of newly developed metal filament lamps. The company was able to offset the cost of converting the customer's equipment by the resulting saving in distribution conductors cost. This became the model for electrical distribution in Germany and the rest of Europe and the 220 V system became common. North American practice remained with voltages near 110 V for lamps.
The stability of the voltage and frequency supplied to customers varies among countries and regions. "Power quality" is a term describing the degree of deviation from the nominal supply voltage and frequency. Short-term surges and drop-outs affect sensitive electronic equipment such as computers and flat panel displays. Longer-term power outages, brown-outs and black outs and low reliability of supply generally increase costs to customers, who may have to invest in uninterruptible power supply or stand-by generator sets to provide power when the utility supply is unavailable or unusable. Erratic power supply may be a severe economic handicap to businesses and public services which rely on electrical machinery, illumination, climate control and computers. Even the best quality power system may have breakdowns or require servicing. As such, companies, governments and other organizations sometimes have backup generators at sensitive facilities, to ensure that power will be available even in the event of a power outage or black out.