Тұрмыстық электр қуаты түрлері мен ерекшеліктері

Type of lower voltage electricity most commonly provided by utilities

Mains electricity or utility power, grid power, domestic power, and wall power, or, in some parts of Canada, hydro, is a general purpose alternating current (AC) electric power supply. It is the form of electrical power that is delivered to homes and businesses through the electrical grid in many parts of the world. People use this electricity to power everyday items (such as domestic appliances, televisions and lamps) by plugging them into a wall outlet. The voltage and frequency of electric power differs between regions. In much of the world, a voltage (nominally) of 230 volts and frequency of 50 Hz is used. In North America, the most common combination is 120 V and a frequency of 60 Hz. Other combinations exist, for example, 230 V at 60 Hz. Travellers' portable appliances may be inoperative or damaged by foreign electrical supplies. Non interchangeable plugs and sockets in different regions provide some protection from accidental use of appliances with incompatible voltage and frequency requirements.

In the US, mains electric power is referred to by several names including "utility power", "household power", "household electricity", "house current", "powerline", "domestic power", "wall power", "line power", "wall current", "AC power", "city power", "street power", and "120 (one twenty)". 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 as "hydro" in some regions of the country. This is also reflected in names of current and historical electricity utilities such as Hydro Québec, BC Hydro, Manitoba Hydro, Hydro One and Newfoundland and Labrador Hydro.

Portable appliances use single phase electric power, with two or three wired contacts at each outlet. Two wires (neutral and live/active/hot) carry current to operate the device. A third wire, not always present, connects conductive parts of the appliance case to earth ground. This protects users from electric shock if live internal parts accidentally contact the case. In northern and central Europe, residential electrical supply is commonly 400 V three phase electric power, which gives 230 V between any single phase and neutral; house wiring may be a mix of three phase and single phase circuits, but three phase residential use is rare in the UK. High power appliances such as kitchen stoves, water heaters and household power heavy tools like log splitters may be supplied from the 400 V three phase power supply. 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). Larger household electrical equipment and industrial equipment may be permanently wired to the fixed wiring of the building. For example, in North American homes a window mounted self contained air conditioner unit would be connected to a wall plug, whereas the central air conditioning for a whole home would be permanently wired. Larger plug and socket combinations are used for industrial equipment carrying larger currents, higher voltages, or three phase electric power. Circuit breakers and fuses are used to detect short circuits between the line and neutral or ground wires or the drawing of more current than the wires are rated to handle (overload protection) to prevent overheating and possible fire. These protective devices are usually mounted in a central panel—most commonly a distribution board or consumer unit—in a building, but some wiring systems also provide a protection device at the socket or within the plug. Residual current devices, also known as ground fault circuit interrupters and appliance leakage current interrupters, are used to detect ground faults—flow of current in other than the neutral and line wires (like the ground wire or a person). When a ground fault is detected, the device quickly cuts off the circuit.

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 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 United States and Canada use a supply voltage of 120 volts ± 6%. Japan, Taiwan, Saudi Arabia, North America, Central America and some parts of northern South America use a voltage between 100 V and 127 V. However, most of the households in Japan equip split phase electric power like the United States, which can supply 200 V by using reversed phase at the same time. Brazil is unusual in having both 127 V and 220 V systems at 60 Hz and also permitting interchangeable plugs and sockets. Saudi Arabia and Mexico have mixed voltage systems; in residential and light commercial buildings both countries use 127 volts, with 220 volts at 60 Hz in commercial and industrial applications. The Saudi government approved plans in August 2010 to transition the country to a totally 230/400 volt 60 Hz system.

A distinction should be made between the voltage at the point of supply (nominal voltage at the point of interconnection between the electrical utility and the user) and the voltage rating of the equipment (utilization or load voltage). Typically the utilization voltage is 3% to 5% lower than the nominal system voltage; for example, a nominal 208 V supply system will be connected to motors with "200 V" on their nameplates. This allows for the voltage drop between equipment and supply. Voltages in this article are the nominal supply voltages and equipment used on these systems will carry slightly lower nameplate voltages. Power distribution system voltage is nearly sinusoidal in nature. Voltages are expressed as root mean square (RMS) voltage. Voltage tolerances are for steady state operation. Momentary heavy loads, or switching operations in the power distribution network, may cause short term deviations out of the tolerance band and storms and other unusual conditions may cause even larger transient variations. In general, power supplies derived from large networks with many sources are more stable than those supplied to an isolated community with perhaps only a single generator.

The choice of supply voltage is due more to historical reasons than optimization of the electric power distribution system—once a voltage is in use and equipment using this voltage is widespread, changing voltage is a drastic and expensive measure. A 230 V distribution system will use less conductor material than a 120 V system to deliver a given amount of power because the current, and consequently the resistive loss, is lower. While large heating appliances can use smaller conductors at 230 V for the same output rating, few household appliances use anything like the full capacity of the outlet to which they are connected. Minimum wire size for hand held or portable equipment is usually restricted by the mechanical strength of the conductors. Many areas, such as the US, which use (nominally) 120 V, make use of three wire, split phase 240 V systems to supply large appliances. In this system a 240 V supply has a centre tapped neutral to give two 120 V supplies which can also supply 240 V to loads connected between the two line wires. Three phase systems can be connected to give various combinations of voltage, suitable for use by different classes of equipment. Where both single phase and three phase loads are served by an electrical system, the system may be labelled with both voltages such as 120/208 or 230/400 V, to show the line to neutral voltage and the line to line voltage. Large loads are connected for the higher voltage. Other three phase voltages, up to 830 volts, are occasionally used for special purpose systems such as oil well pumps. Large industrial motors (say, more than 250 hp or 150 kW) may operate on medium voltage. On 60 Hz systems a standard for medium voltage equipment is 2,400/4,160 V whereas 3,300 V is the common standard for 50 Hz systems.

Until 1987, mains voltage in large parts of Europe, including Germany, Austria and Switzerland, was 220 while the UK used 240. Standard ISO IEC 60038:1983 defined the new standard European voltage to be 230. From 1987 onwards, a step wise shift towards 230 was implemented. From 2009 on, the voltage is permitted to be 230. No change in voltage was required by either the Central European or the UK system, as both 220 V and 240 V fall within the lower 230 V tolerance bands (230 V ±6%). Usually the voltage of 230V ±3% is maintained. Some areas of the UK still have 250 volts for legacy reasons, but these also fall within the 10% tolerance band of 230 volts. In practice, this allowed countries to have supplied the same voltage (220 or 240 V), at least until existing supply transformers are replaced. Equipment (with the exception of filament bulbs) used in these countries is designed to accept any voltage within the specified range. In 2000, Australia converted to 230 V as the nominal standard with a tolerance of +10%/−6%, this superseding the old 240 V standard, AS 2926 1987. The tolerance was increased in 2022 to ± 10% with the release of AS IEC 60038:2022. The utilization voltage available at an appliance may be below this range, due to voltage drops within the customer installation. As in the UK, 240 V is within the allowable limits and "240 volt" is a synonym for mains in Australian and British English. In the United States and Canada, 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%). Historically, 110 V, 115 V and 117 V have been used at different times and places in North America. Mains power is sometimes spoken of as 110 V; however, 120 V is the nominal voltage. 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. To accommodate the difference, frequency sensitive appliances marketed in Japan can often be switched between the two frequencies.

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. The world's first large scale central plant—Thomas Edison's steam powered station at Holborn Viaduct in London—started operation in January 1882, providing direct current (DC) at 110 V. The Holborn Viaduct station was used as a proof of concept for the construction of the much larger Pearl Street Station in New York, the world's first permanent commercial central power plant. The Pearl Street Station also provided DC at 110 V, considered to be a "safe" voltage for consumers, beginning 4 September 1882. AC systems started appearing in the US in the mid 1880s, using higher distribution voltage stepped down via transformers to the same 110 V customer utilization voltage that Edison used. 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. By connecting two groups of 110 V lamps in series more load could be served by the same size conductors run with 220 V between them; a neutral conductor carried any imbalance of current between the two sub circuits. 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. After World War II the standard voltage in the U. S. became 117 V, but many areas lagged behind even into the 1960s. In 1954, the American National Standards Institute (ANSI) published C84.1 “American National Standard for Electric Power Systems and Equipment – Voltage Ratings (60 Hertz)”. This standard established 120 volt nominal system and two ranges for service voltage and utilization voltage variations. Today, virtually all American homes and businesses have access to 120 and 240 V at 60 Hz. Both voltages are available on the three wires (two "hot" legs of opposite phase and one "neutral" leg). In 1899, the Berliner Elektrizitäts 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. 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. The most common frequency was 133⅓ Hz. 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. Around 1893 the Westinghouse Electric Company in the United States and AEG in Germany decided to standardize their generation equipment on 60 Hz and 50 Hz respectively, eventually leading to most of the world being supplied at one of these two frequencies. Today most 60 Hz systems deliver nominal 120/240 V, and most 50 Hz nominally 230 V. The significant exceptions are in Brazil, which has a synchronized 60 Hz grid with both 127 V and 220 V as standard voltages in different regions, and Japan, which has two frequencies: 50 Hz for East Japan and 60 Hz for West Japan.

To maintain the voltage at the customer's service within the acceptable range, electrical distribution utilities use regulating equipment at electrical substations or along the distribution line. At a substation, the step down transformer will have an automatic on load tap changer, allowing the ratio between transmission voltage and distribution voltage to be adjusted in steps. For long (several kilometres) rural distribution circuits, automatic voltage regulators may be mounted on poles of the distribution line. These are autotransformers, again, with on load tap changers to adjust the ratio depending on the observed voltage changes. At each customer's service, the step down transformer has up to five taps to allow some range of adjustment, usually ±5% of the nominal voltage. Since these taps are not automatically controlled, they are used only to adjust the long term average voltage at the service and not to regulate the voltage seen by the utility customer.

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, brownouts and blackouts 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. Power quality can also be affected by distortions of the current or voltage waveform in the form of harmonics of the fundamental (supply) frequency, or non harmonic (inter)modulation distortion such as that caused by electromagnetic interference. In contrast, harmonic distortion is usually caused by conditions of the load or generator. In multi phase power, phase shift distortions caused by imbalanced loads can occur.