Mains electricity
People use this electricity to power everyday items (such as domestic appliances, televisions and lamps) by plugging them into a wall outlet.
Non-interchangeable plugs and sockets in different regions provide some protection from accidental use of appliances with incompatible voltage and frequency requirements.
More than half of power in Canada is hydroelectricity, and mains electricity is often referred to as "hydro" in some regions of the country.
Foreign enclaves, such as large industrial plants or overseas military bases, may have a different standard voltage or frequency from the surrounding areas.
Many other combinations of voltage and utility frequency were formerly used, with frequencies between 25 Hz and 133 Hz and voltages from 100 V to 250 V. Direct current (DC) has been displaced by alternating current (AC) in public power systems, but DC was used especially in some city areas to the end of the 20th century.
This protects users from electric shock if live internal parts accidentally contact the case.
Small portable electrical equipment is connected to the power supply through flexible cables terminated in a plug, which is inserted into a fixed receptacle (socket).
Most of the world population (Europe, Africa, Asia, Australia, New Zealand, and much of South America) use a supply that is within 6% of 230 V. In the United Kingdom[5] the nominal supply voltage is 230 V +10%/−6% to accommodate the fact that most transformers are in fact still set to 240 V. The 230 V standard has become widespread so that 230 V equipment can be used in most parts of the world with the aid of an adapter or a change to the equipment's plug to the standard for the specific country.
The Saudi government approved plans in August 2010 to transition the country to a totally 230/400-volt 60 Hz system.
Minimum wire size for hand-held or portable equipment is usually restricted by the mechanical strength of the conductors.
Three-phase systems can be connected to give various combinations of voltage, suitable for use by different classes of equipment.
In the United States[12][13] and Canada,[14] national standards specify that the nominal voltage at the source should be 120 V and allow a range of 114 V to 126 V (RMS) (−5% to +5%).
In Japan, the electrical power supply to households is at 100 and 200 V. Eastern and northern parts of Honshū (including Tokyo) and Hokkaidō have a frequency of 50 Hz, whereas western Honshū (including Nagoya, Osaka, and Hiroshima), Shikoku, Kyūshū and Okinawa operate at 60 Hz.
The boundary between the two regions contains four back-to-back high-voltage direct-current (HVDC) substations which interconnect the power between the two grid systems; these are Shin Shinano, Sakuma Dam, Minami-Fukumitsu, and the Higashi-Shimizu Frequency Converter.
The world's first public electricity supply was a water wheel driven system constructed in the small English town of Godalming in 1881.
The Pearl Street Station also provided DC at 110 V, considered to be a "safe" voltage for consumers, beginning 4 September 1882.
In 1883, Edison patented a three–wire distribution system to allow DC generation plants to serve a wider radius of customers to save on copper costs.
AC circuits adopted the same form during the war of the currents, allowing lamps to be run at around 110 V and major appliances to be connected to 220 V. Nominal voltages gradually crept upward to 112 V and 115 V, or even 117 V.[citation needed] After World War II the standard voltage in the U.S. became 117 V, but many areas lagged behind even into the 1960s.
[19] In the first decade after the introduction of alternating current in the US (from the early 1880s to about 1893) a variety of different frequencies were used, with each electric provider setting their own, so that no single one prevailed.
[citation needed] The rotation speed of induction generators and motors, the efficiency of transformers, and flickering of carbon arc lamps all played a role in frequency setting.
These are autotransformers, again, with on-load tap changers to adjust the ratio depending on the observed voltage changes.
"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.
Erratic power supply may be a severe economic handicap to businesses and public services which rely on electrical machinery, illumination, climate control and computers.
