Electrical Power Distribution

What is Electrical Power Distribution: Let us know about Electrical Power Distribution. The final step in electric power distribution is the distribution of electricity ; It carries electricity from the transmission system to individual consumers. Distribution substations connect to the transmission system and reduce the transmission voltage to medium voltage2 kV and With the use of 35 kV transformer . [1] Primary distribution lines carry this medium voltage power to distribution transformers located near the customer’s premises . Distribution transformers again reduce the voltage to the use voltage used by lighting, industrial equipment and home appliances. Often multiple customers are supplied from a single transformer through secondary distribution lines. Commercial and residential customers are connected to secondary distribution lines through service drops . Customers demanding high volumes of electricity may be connected directly to the primary distribution level or sub transmission Level.

Electrical Power Distribution

The transition from transmission to distribution occurs in a power substation , which has the following functions:

  • Circuit breakers and switches enable the substation to be disconnected from the transmission grid or to disconnect the distribution lines.
  • Transformers reduce the transmission voltage,35 kV or more, below the primary distribution voltage. These are medium voltage circuits, usually600-35 000 V.
  • From the transformer, the power goes to the busbar which can split the distribution power in multiple directions. The bus distributes electricity to the distribution lines, which is passed on to the customers.

Urban distribution is mainly underground, sometimes in general utility ducts . Rural distribution is mostly above ground with utility poles , and suburban distribution is a mix. [1] Close to the subscriber, a distribution transformer moves the primary distribution power to a low-voltage secondary circuit, typically 120/240 V in the US for residential customers. Customer gets electricity through service drop and electricity meter . The final circuit may be less than 15 m (50 ft) in an urban system, but may exceed 91 m (300 ft) for a rural subscriber.


Electricity distribution only became necessary in the 1880s when power stations began to generate electricity . Prior to this, electricity was usually generated where it was used. The first power distribution systems installed in European and American cities were used to supply lighting: arc lighting operating at very high voltages (about 3000 volts), alternating current (AC) or direct current (DC), and low voltage. Incandescent light operating on (100 volts) direct current. [3] Both gas lighting systems, with arc lighting occupying large areas and street lighting, and incandescent lighting replacing gas for business and residential lighting.

Due to the high voltage used in arc lighting, a single generating station can supply a long string of lights for up to a 7-mile (11 km) long circuit. [4] Each doubling of the voltage will allow the same size cable to transmit the same amount of power to four times the distance for a given power loss. Direct current indoor incandescent lighting, for example the first Edison Pearl Street station installed in 1882, had difficulty supplying customers more than a mile away. This was due to the use of low 110 volt systems throughout the system from generator to end use. The Edison DC system required thick copper conductor cables, and production plants had to be within about 1.5 miles (2.4 km) of the farthest customer to avoid overly large and costly conductors.

Introduction to Transformer

Transmitting power over long distances at high voltages and then reducing it to low voltages for lighting became a recognized engineering roadblock for power distribution, with many, not very satisfactory, solutions tested by lighting companies. The mid-1880s saw a breakthrough with the development of functional transformers that allowed the AC voltage to be “stepped up” to a much higher transmission voltage and then dropped to a lower end user voltage. With much cheaper transmission costs and greater economies of scale of large production plants supplying entire cities and regions, the use of ACs spread rapidly. (Electrical Power Distribution)

The competition between direct current and alternating current in the US took a personal turn in the late 1880s in the form of the ” War of Currents “, when Thomas Edison began attacking George Westinghouse and designed the first US AC transformer system. Pointing out all the way to development. The deaths due to high voltage AC systems over the years and claiming any AC system was inherently dangerous. [5] Edison’s campaign was short-lived and his company adopted AC in 1892.

In Europe and America, AC became the dominant form of power transmission with innovations in electric motor design and the development of engineered universal systems connecting a large number of legacy systems to the larger AC grid. [6] [7]

In the first half of the 20th century, in many places the electric power industry was vertically integrated, meaning that a single company did generation, transmission, distribution, metering and billing. Starting in the 1970s and 1980s, nations began a process of deregulation and privatization, which led to an increase in electricity markets. Distribution systems would remain regulated, but production, retail, and sometimes transmission systems were replaced in competing markets.

generation and transmission

Electrical power begins at a generating station, where the potential difference can be as high as 33,000 volts. AC is commonly used. Users of large amounts of DC power, such as some railway electrification systems, telephone exchanges, and industrial processes such as aluminum smelting, use rectifiers to obtain DC from public AC supplies, or may have their own generation systems. High-voltage DC can be beneficial for isolating alternating-current systems or controlling the amount of power dissipated. For example, Hydro-Québec has a direct-current line that runs from the James Bay area to Boston.(Electrical Power Distribution)

From the generating station it travels to the switchyard of the generating station where a step-up transformer steps up the voltage from 44 kV to 765 kV to a level suitable for transmission. Once in the transmission system, the electricity from each generating station is combined with the electricity produced elsewhere. Electricity is consumed as soon as it is generated. It travels very fast, close to the speed of light.

primary distribution

The primary distribution voltage ranges from 4 kV to 35 kV phase-to-phase (2.4 kV to 20 kV phase-to-neutral) [9] only large consumers fed directly from the distribution voltage; Most utility customers are connected to a transformer, which converts the distribution voltage to the low voltage “use voltage”, “supply voltage” or “mains voltage” used by lighting and internal wiring systems.

Network configuration

Distribution networks are divided into two types, radial or network. [10] A radial system is arranged like a tree where each customer has a single source of supply. A network system consists of multiple sources of supply working in parallel. Spot networks are used for concentrated loads. Radial systems are typically used in rural or suburban areas.

Radial systems typically include emergency connections, where the system can be reconfigured in case of a problem, such as a fault or planned maintenance. This can be done by opening and closing switches to isolate a certain section from the grid.

Long feeders experience voltage drop (power factor distortion), which requires the installation of capacitors or voltage regulators.

Electrical Power Distribution: Reconfiguration, by exchanging functional links between system elements, represents one of the most important measures that can improve the operational performance of a distribution system. The problem of optimization through reconfiguration of an electricity distribution system is, in the context of its definition, a historical single-purpose problem with constraints. Since 1975, when Marilyn and Beck [11]introduced the idea of ​​reconfiguration of the distribution system for active power loss reduction, to date, many researchers have proposed a variety of methods and algorithms to solve the reconfiguration problem as a single-purpose problem. Some authors have proposed a Pareto optimality based approach (including active power loss and reliability indices as objectives). For this purpose, various artificial intelligence based methods have been used: microgenetic, [12] branch exchange, [13] particle swarm optimization [14] and non-dominated sorting genetic algorithm. (Electrical Power Distribution)

rural services

Rural electrification systems use higher distribution voltages due to the longer distance covered by distribution lines (see Rural Electrification Administration). 7.2, 12.47, 25, and 34.5 kV distribution is common in the United States; 11 kV and 33 kV are common in the UK, Australia and New Zealand; 11 kV and 22 kV are common in South Africa; 10, 20 and 35 kV are common in China. [16] Other voltages are sometimes used.

Rural services generally try to reduce the number of poles and wires. It uses higher voltage (compared to urban distribution), which in turn allows the use of galvanized steel wire. Sturdy steel wire allows for less expensive wide pole spacing. In rural areas a pole-mount transformer can serve only one customer. In New Zealand, Australia, Saskatchewan, Canada, and South Africa, single wire earth return systems (SWER) are used to deliver electricity to remote rural areas.

Three-phase service provides electricity for large agricultural facilities, petroleum pumping facilities, water plants, or other customers that have large loads (three-phase equipment). In North America, overhead distribution systems may be three-phase, four-wire with a neutral conductor. Rural distribution systems may have long runs of one phase conductor and one neutral. [17] In other countries or in extreme rural areas the neutral wire is connected to ground to be used as a return (single-wire earth return). This is called an ungrounded Y system.

secondary distribution

Electrical Power Distribution

Electricity is delivered at a frequency of 50 or 60 Hz, depending on the region. It is supplied to domestic customers as single phase electric power. In some countries, such as Europe, three-phase supply may be provided for large properties. Viewed with an oscilloscope, home power supplies in North America look like a sine wave, oscillating between -170 volts and 170 volts, giving an effective voltage of 120 volts RMS. [18] Three-phase electric power is more efficient in terms of power per cable used, and is more suitable for driving larger electric motors. Some large European appliances may be powered by three-phase power, such as electric stoves and clothes dryers.

A ground connection is typically provided for the customer’s system as well as utility-owned equipment. The purpose of connecting a customer’s system to ground is to limit the voltage that can develop if high-voltage conductors fall on low-voltage conductors that are typically grounded, or if a failure occurs within the distribution transformer. . Earthing systems can be TT, TN-S, TN-CS or TN-C.

regional variations

220-240 volt systems

Electrical Power Distribution: Most of the world uses 50 Hz 220 or 230 V single phase, or 400 V 3 phase for residential and light industrial services. In this system, the primary distribution network supplies a few substations per area, and 230 V/400 V power from each substation is distributed directly to users in an area normally less than 1 km in radius. The three live (hot) wires and the neutral are connected to the building for three-phase service. Single-phase distribution, with a live wire and neutral used in households where the total load is lighter. In Europe, electricity for industry and domestic use is typically distributed by a three-phase, four-wire system. This is the phase-to-phase voltage of 400 volts Y service and 230 volts between any one phase and neutral. gives a single-phase voltage of . A typical urban or suburban low-voltage substation in the UK will typically be rated between 150 kVA and 1 MVA and will supply an entire neighborhood of a few hundred homes. Transformers are typically sized at an average load of 1 to 2 kW per household, and service fuses and cables are sized to allow a single property to draw ten times the maximum load possible. For industrial customers, 3-phase 690/400 volts is also available, or can be generated locally. [19] Large industrial customers have their own transformers with inputs from 11 kV to 220 kV.

100–120 volt systems

Most Americans use 60 Hz AC, 120/240 volt split-phase systems for household and three-phase large installations. North American transformers typically power homes at 240 volts, similar to Europe’s 230 volts. It is split-phase which allows the use of 120 volts in the home.

In the power sector in Japan, the standard voltage is 100 V, with both 50 and 60 Hz AC frequencies being used. Some parts of the country use 50 Hz, while other parts use 60 Hz. [20] It is a relic from the 1890s. Some local providers in Tokyo imported 50 Hz German equipment, while local electricity providers in Osaka brought 60 Hz generators from the United States. The grid grew until eventually the entire country was wired. Today the frequency is 50 Hz in eastern Japan (including Tokyo, Yokohama, Thoku and Hokkaido) and 60 Hz in western Japan (including Nagoya, Osaka, Kyoto, Hiroshima, Shikoku and Kyushu). [21]

Most home appliances are made to operate on either frequency. The problem of dissonance came into public view when the 2011 Thoku earthquake and tsunami dropped about a third of the east’s capacity, and power in the west could not be fully shared with the east, as the country had a common frequency. Not there. [20]

There are four high-voltage direct current (HVDC) converter stations that carry electricity across Japan’s AC frequency border. Shin Shinano is a back-to-back HVDC facility in Japan that forms one of four frequency converter stations connecting Japan’s western and eastern power grids. The other three are at Higashi-Shimizu, Minami-Fukumitsu and Sakuma Dam. Together they can move up to 1.2 GW of electricity to the east or west. [22]

240 volt system and 120 volt outlet

Most modern North American homes are wired to receive 240 volts from transformers, and through the use of split-phase electrical power, can have both 120 volt receptacles and 240 volt receptacles. 120 volts is commonly used for lighting and most wall outlets. 240 volt circuits are commonly used for appliances requiring high wattage heat output such as ovens and heaters. They can also be used to supply electric car chargers.

modern distribution system

Traditionally, distribution systems operate only as simple distribution lines, where power from the transmission network is shared between customers. Today’s distribution systems are heavily integrated with renewable energy generations at the distribution level of power systems through distributed generation resources such as solar power and wind power. [23] As a result, the distribution system is becoming more independent from the transmission network day by day. Balancing the supply-demand relationship on these modern distribution networks (sometimes referred to as microgrids) is extremely challenging, and requires the use of a variety of technical and operational tools to operate. Such tools include battery storage power stations, data analytics, optimization tools, etc.