Electric distribution network
|This article needs additional citations for verification. (June 2015) (Learn how and when to remove this template message)|
The electric distribution network is a power delivery system consisting of cables that deliver electric power from its point of generation to the end users. Electrical distribution systems are primarily designed to meet the consumer's demands for energy. This is achieved by taking energy from primary substations and delivering it to various customer substations through either underground cables or above ground lines. Because of the lack of space, some cities and towns primarily rely more on underground cables and rural areas lean more towards overhead lines. Choosing between underground or above grounds methods can depend on how much protection and control can be provided. When it comes to choosing which method is best for the area, there are three components of planning that are taken into consideration: long term planning, network planning, and construction planning. Long term planning refers to thinking ahead, or in other words, thinking of the future. There are some questions that should be taken into account when using this method, for instance, if there was a new establishment that needed an energy supply, would there be an easy fix to add on to the network? This also falls directly into network planning which should make the distribution easier to manage if conducted effectively. Furthermore, construction planning is all the engineering work and actual mapping that goes into electrical distribution. These distribution systems help to provide each home, business, and other organizations with electricity in order to perform daily functions. For example, some of the functions include keeping the refrigerator running to prevent spoilage of food or lighting up a room with artificial light. Having a reliable system is essential for productivity and the less mistakes that need to be fixed, the more efficient a business can run.
The entire network consists of the following parts:
The first electric distribution system in the United States was built by Thomas Edison in 1882. Even though it was not the first one in the world at that time on account of Edison having built one earlier that same year in London, it was nonetheless an impressive accomplishment. From his power station, which was known as Pearl Street station, Edison was able to provide power to houses within an area of a square mile. This contribution was Edison's 106th successfully completed patent, and his most successful one thus far. The electric distribution system was an impressive feature and astonished even the most prestigious newspapers. The New York Times described the newly lit light bulbs as:
"Soft, mellow and graceful to the eye…without a particle of flicker to make the head ache" -New York Times 
While Edison's innovation received quite a bit of publicity and praise, it was not economically successful because the amount of money it cost to create and keep the system running was far greater than the profit the system was capable of generating. The small area of lower Manhattan used 100,000 feet of underground wiring which at that time came to $300,000 and which also failed to turn any profit until two years later in 1884. Electric distribution systems were not economically profitable until the switch was made from Edison's direct current (DC) to the alternating current (AC) developed by Nikola Tesla and George Westinghouse among others. With that being said, Edison's work was revolutionary for the time period because it allowed the energy user to be separate from the energy source, and also electric lights were safer than coal, candles, and lamps which often started accidental fires. DC currents are still being used today in mobile phones and computers, which is why one needs an AC adapter when plugging these devices into a socket. Some small areas of cities also use a DC system which then connects to the AC system around the area.
Edison's work eventually led to the creation of the North American and the European electrical distribution systems. These systems are interconnected giving a "gigantic" dimension to this network; however, its control still remains limited in scale (on the level of each country). The control of this system within each jurisdiction is currently very centralized on the level of each electric company or network operator, whereas any disturbances can be global. There are two major types of disturbances, a blackout which is region wide and which can also be transmission related. Blackouts have the ability to affect whole regions, and although this is rare in the United States, it can still happen and it has been known to happen. The second disturbance is a smaller more localized version of the first, and it is distribution related. Distribution systems malfunction more often because of smaller issues such as overhead lines coming into contact with trees, extreme weather conditions, or even animals that come in contact with certain components of an electrical distribution network.
There have been many cases of country wide outages. For example, on November 4, 2006 an electrical line in the North of Germany resulted in a large disturbance across Europe. A similar incident also occurred in the United States affecting a large portion of the Eastern United States as well as a part of Canada.
Global Design of Distribution Networks
Usually the electric utility system is divided into three sub-systems: generation, transmission, and distribution. Sometimes there is a fourth division which is called a sub-transmission. However, the latter is really more of a subset of transmission, since the voltage levels and protection practices are very similar.
The distribution system is often broken down into three components: distribution substation, distribution primary, and secondary. At the substation level, the voltage is reduced and the power is distributed into smaller amounts to the consumers. Accordingly, one substation will supply many consumers with power; therefore, the number of transmission lines in the distribution system is for the most part the number of transmission systems. Most consumers are connected to only one of the three phases in the distribution system. As a result, the power flow on each of the lines is different and the system is typically ‘unbalanced’. This characteristic needs to be accounted for in load flow studies related to distribution networks.
Advantages in distribution system designs can evolve the present day systems. The distribution system is possible of taking advantage of computer and communication gains; some of which include more automation, better communication, between equipment, along with smarter switches and controllers. In addition, this future system can evolve to be able to support widespread distributed generation and storage as well as the ability to charge electric vehicles, however, this cannot happen overnight; such a system will require directional relaying for re-closers, adequate communication between devices, regulators that have advanced controls, and information and control of distributed generators. These advances can make electrical distribution networks more flexible, thus improving power quality and aesthetic value.
Differences between North American and European Distribution Systems
North America and Europe are examples of countries that have electrical distribution systems that have evolved to have two different major designs. Despite their differences, the two designs share similarities which consist of the same hardware such as: conductors, cables, arresters, regulators, and transformers. Furthermore, both of these systems are similar in that they are being radial with similar power carrying capabilities. When the two designs were compared, their major differences were layouts, configurations, and applications in relation to cost, flexibility, safety, reliability, power quality, aesthetics, and theft. The North American distribution system tends to have a more flexible primary design that works well for rural systems and areas where the load is spread out, whereas Europe has a more flexible secondary design that works best for urban systems. Though the North American distribution system by design is safer and more reliable, resulting in fewer consumer interruptions and accidents, the European distribution system is more expensive, allowing for an aesthetic advantage and better power quality.
European systems, as opposed to North American designs, have larger transformers. These increase results in more customers per transformer on account of most European transformers being three-phase and on the order of 300 to 1000 kVA. This is much larger than typical North American 25- or 50-kVA single-phase units. Secondary voltages have influenced many of the differences in distribution systems. For instance, North America has standardized on a 120/240-V secondary system that has voltage drop constrains on how far utilities can run secondaries (which is typically no more than 250 ft). In European designs, higher secondary voltages allow secondaries to stretch to almost 1 mi, and have a standard secondary voltage of 220, 230, or 240 V. The European voltage is twice the size of the North American standard. Although the North American and the European distribution system designs have their advantages and disadvantages, both are examples of successful systems that allow electricity to be provided at the demand of the customer.
- Short, T. A. (2004). Electric Power Distribution Handbook. CRC Press LLC. ISBN 0-8493-1791-6. Retrieved 15 November 2014.
- Chan, F.C. "Electrical Power Distribution Systems" (PDF). www.eolss.net. Encyclopedia of Life Support Systems (EOLSS). Retrieved 14 November 2014.
- "Electricity Distribution". Institute For Energy Research (IER). Retrieved 15 November 2014.
- "Bulk Electricity Grid Beginnings" (PDF). http://www.pearlstreetinc.com/NYISO_bulk_elect_beginnings.pdf. New York Independent System Operator (NYISO). Retrieved 20 November 2014. External link in
- Sabonnadiere, Jean-Claude (2011). Electric Distribution Networks. ISTE Ltd. p. 460. ISBN 978-1-84821-245-9.
- Cugnet, P. "Power Distribution Systems" (PDF). Virginia Tech. Digital Library and Archives. Retrieved 21 November 2014.