Electricity distribution Guide, Meaning , Facts, Information and Description
Electricity distribution is the penultimate process in the delivery of electric power, i.e. the part between transmission and user purchase from a retailer. It is generally considered to include medium-voltage (less then 50kV) power lines, low-voltage electrical substations and pole-mounted transformers, low-voltage (less than 1000V) distribution wiring and sometimes electricity meters.
Other processes in power delivery are generation, transmission and retailing.
In the early days of electricity generation, direct current (DC) generators were connected to loads at the same voltage. This imposed limitations on how far the distribution system could extend because of the voltage drop. It also meant that cables and lines had to be made from relatively large diameter copper in order to carry the high currentss required to meet the demand of distributed load. (Power lost in generating heat in a conductor is proportional to the square of the current; i.e., Losses = I2R. These losses can be reduced by reducing the resistance (R) of the conductor, hence increasing the diameter; or, more effectively, by reducing the current (I).)
The adoption of alternating current (AC) for electricity generation following the War of Currents dramatically changed the situation. Power transformers could be used to raise the voltage from the generators and reduce it to supply loads. Increasing the voltage reduced the current and hence the size of conductors and distribution losses, making it more economic to distribute power over long distances. The ability to transform to extra-high voltages enabled generators to be located far from loads and transmission systems to interconnect generating stations and distribution networkss.
In North America, early distribution systems were single phase and used a voltage of 2200 volts corner-grounded delta. Over time, this was gradually increased to 2400 volts. As cities grew and the use of three-phase power became more widespread, most 2400 volt systems were upgraded to 2400/4160Y three-phase systems, which also benefitted from better surge suppression due to the grounded neutral. Some city and suburban distribution systems continue to use this range of voltages, but most have been converted to 7200/12470Y.
European systems used higher voltages, generally 3300 volts to ground, in support of the 220Y/380 volt power systems used in those countries. In the UK, urban sysytems progressed to 6.6 kV and then 11 kV, the most common distribution voltage.
North American and European power distribution systems also differ in that North American systems tend to have a greater number of low-voltage step-down transformers located closer to customers' premises. For example, in the US a pole-mounted transformer in a suburban setting may supply only a single or a very few houses, whereas in the UK a typical urban or suburban low-voltage substation might be rated at 2MW and supply a whole neighbourhood. This is because the higher voltage used in Europe (230V vs 120V) may be carried over a greater distance without unacceptable power loss. An advantage of the North American setup is that failure or maintenance on a single transformer will only affect a few customers. Advantages of the UK setup are that fewer transformers are required; larger and more efficient transformers are used, and due to diversity there need be less spare capacity in the transformers, reducing power wastage.
Rural Electrification systems, in contrast to urban systems, tend to use higher voltages because of the longer distances covered by those distribution lines. 7200 volts is commonly used in the United States; 11kV and 33kV are common in the UK. Other voltages are occasionally used in unusual situations or where a local utility simply has engineering practices that differ from the norm.
In New Zealand, Australia and South Africa, single wire earth return systems (SWER) are used to electrify remote rural areas.
Characteristics of the supply given to customers are generally mandated by law and by contract between the supplier and customer. Variables include:
- AC or DC (virtually all public electricity supplies are AC today. Users of large amounts of DC power such as some electric railways, telephone exchanges and industrial processes such as aluminium smelting either operate their own generating equipment or have equipment to derive DC from the public AC supply)
- voltage, including tolerance (usually + or - a certain percentage)
- frequency (50Hz and 60Hz are most common)
- maximum current that may be drawn
- phase configuration (single phase, split phase, polyphase including two phase and three phase)
- power factor
- maximum prospective short circuit current
Electricity industry reform has led to the creation of electricity markets through the separation of contestable retailing from distribution, a natural monopoly and the separation of the monopoly transmission from generation. It also led to the development of new terminology to describe the distributor such as Line company, Wires Business and Network Company.
See also Distributed generation.
| U.S. | U.K. |
| Groundeded | Earthed |
| Wye or Y | Star |
This is an Article on Electricity distribution. Page Contains Information, Facts Details or Explanation Guide About Electricity distribution