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Electric power distribution is the final stage in the delivery of electric power; it carries electricity from the transmission system to individual consumers. Distribution substations connect to the transmission system and lower the transmission voltage to medium voltage ranging between 2 kV and 35 kV with the use of transformers. Primary distribution lines carry this medium voltage power to distribution transformers located near the customer's premises. Distribution transformers again lower the voltage to the utilization voltage used by lighting, industrial equipment and household appliances. Often several customers are supplied from one transformer through secondary distribution lines. Commercial and residential customers are connected to the secondary distribution lines through service drops. Customers demanding a much larger amount of power may be connected directly to the primary distribution level or the subtransmission level.
Distributed generation, also distributed energy, on-site generation (OSG), or district/decentralized energy, is electrical generation and storage performed by a variety of small, grid-connected or distribution system-connected devices referred to as distributed energy resources (DER).
The utility frequency, (power) line frequency or mains frequency is the nominal frequency of the oscillations of alternating current (AC) in a wide area synchronous grid transmitted from a power station to the end-user. In large parts of the world this is 50 Hz, although in the Americas and parts of Asia it is typically 60 Hz. Current usage by country or region is given in the list of mains electricity by country.
Electric power quality is the degree to which the voltage, frequency, and waveform of a power supply system conform to established specifications. Good power quality can be defined as a steady supply voltage that stays within the prescribed range, steady a.c. frequency close to the rated value, and smooth voltage curve waveform. In general, it is useful to consider power quality as the compatibility between what comes out of an electric outlet and the load that is plugged into it. The term is used to describe electric power that drives an electrical load and the load's ability to function properly. Without the proper power, an electrical device may malfunction, fail prematurely or not operate at all. There are many ways in which electric power can be of poor quality and many more causes of such poor quality power.
IEC 61850 is an international standard defining communication protocols for intelligent electronic devices at electrical substations. It is a part of the International Electrotechnical Commission's (IEC) Technical Committee 57 reference architecture for electric power systems. The abstract data models defined in IEC 61850 can be mapped to a number of protocols. Current mappings in the standard are to MMS, GOOSE [see section 3, Terms and definitions, term 3.65 on page 14], SV or SMV, and soon to Web Services. In the previous version of the standard, GOOSE stood for "Generic Object Oriented Substation Event", but this old definition is still very common in IEC 61850 documentation. These protocols can run over TCP/IP networks or substation LANs using high speed switched Ethernet to obtain the necessary response times below four milliseconds for protective relaying.
A microgrid is a decentralized group of electricity sources and loads that normally operates, connected to and synchronous with the traditional wide area synchronous grid (macrogrid), but is able to disconnect from the interconnected grid and to function autonomously in "island mode" as technical or economic conditions dictate. In this way, microgrids improve the security of supply within the microgrid cell, and can supply emergency power, changing between island and connected modes.
The IEEE Std 1901-2010 is a standard for high speed communication devices via electric power lines, often called broadband over power lines (BPL). The standard uses transmission frequencies below 100 MHz. This standard is usable by all classes of BPL devices, including BPL devices used for the connection to Internet access services as well as BPL devices used within buildings for local area networks, smart energy applications, transportation platforms (vehicle), and other data distribution applications.
A phasor measurement unit (PMU) is a device used to estimate the magnitude and phase angle of an electrical phasor quantity in the electricity grid using a common time source for synchronization. Time synchronization is usually provided by GPS or IEEE 1588 Precision Time Protocol, which allows synchronized real-time measurements of multiple remote points on the grid. PMUs are capable of capturing samples from a waveform in quick succession and reconstructing the phasor quantity, made up of an angle measurement and a magnitude measurement. The resulting measurement is known as a synchrophasor. These time synchronized measurements are important because if the grid’s supply and demand are not perfectly matched, frequency imbalances can cause stress on the grid, which is a potential cause for power outages.
Islanding is the condition in which a distributed generator (DG) continues to power a location even though external electrical grid power is no longer present. Islanding can be dangerous to utility workers, who may not realize that a circuit is still powered, and it may prevent automatic re-connection of devices. Additionally, without strict frequency control, the balance between load and generation in the islanded circuit can be violated, thereby leading to abnormal frequencies and voltages. For those reasons, distributed generators must detect islanding and immediately disconnect from the circuit; this is referred to as anti-islanding.
ENTSO-E, the European Network of Transmission System Operators, represents 42 electricity transmission system operators (TSOs) from 35 countries across Europe, thus extending beyond EU borders. ENTSO-E was established and given legal mandates by the EU's Third Package for the Internal energy market in 2009, which aims at further liberalising the gas and electricity markets in the EU.
A smart grid is an electrical grid which includes a variety of operation and energy measures including:
The synchronous grid of Continental Europe is the largest synchronous electrical grid in the world. It is interconnected as a single phase-locked 50 Hz mains frequency electricity grid that supplies over 400 million customers in 24 countries, including most of the European Union. In 2009, 667 GW of production capacity was connected to the grid, providing approximately 80 GW of operating reserve margin. The transmission system operators operating this grid formed the Union for the Coordination of Transmission of Electricity (UCTE), now part of the European Network of Transmission System Operators for Electricity (ENTSO-E).
An electrical grid is an interconnected network for electricity delivery from producers to consumers. Electrical grids vary in size and can cover whole countries or continents. It consists of:
A wide area synchronous grid is a three-phase electric power grid that has regional scale or greater that operates at a synchronized utility frequency and is electrically tied together during normal system conditions. Also known as synchronous zones, the most powerful is the synchronous grid of Continental Europe (ENTSO-E) with 859 gigawatts (GW) of generation, while the widest region served is that of the IPS/UPS system serving most countries of the former Soviet Union. Synchronous grids with ample capacity facilitate electricity trading across wide areas. In the ENTSO-E in 2008, over 350,000 megawatt hours were sold per day on the European Energy Exchange (EEX).
IEEE 2030 was a project of the standards association of the Institute of Electrical and Electronics Engineers (IEEE) that developed a "Guide for Smart Grid Interoperability of Energy Technology and Information Technology Operation with the Electric Power System (EPS), and End-Use Applications and Loads".
Ancillary services are the services necessary to support the transmission of electric power from generators to consumers given the obligations of control areas and transmission utilities within those control areas to maintain reliable operations of the interconnected transmission system.
IEEE Smart Grid is an initiative launched by IEEE to help provide expertise and guidance for individuals and organizations involved in the modernization and optimization of the power grid, better known as the "smart grid". IEEE Smart Grid encompasses an array of activities, including development of new smart grid-related standards, best practices, publications, and conferences and educational opportunities.
VERDE is a visualization and analysis capability of the United States Department of Energy (DOE). The system, developed and maintained by Oak Ridge National Laboratory (ORNL), provides wide-area situational understanding of the U.S. electric grid. Enabling grid monitoring, weather impacts prediction and analysis, VERDE supports preparedness and response to potentially large outage events. As a real-time geo-visualization capability, it characterizes the dynamic behavior of the grid over interconnects giving views into bulk transmission lines as well as county-level power distribution status. By correlating grid behaviors with cyber events, the platform also enables a method to link cyber-to-infrastructure dependencies.
The electrical power grid that powers Northern America is not a single grid, but is instead divided into multiple wide area synchronous grids. The Eastern Interconnection and the Western Interconnection are the largest. Three other regions include the Texas Interconnection, the Quebec Interconnection, and the Alaska Interconnection. Each region delivers power at a nominal 60 Hz frequency. The regions are not usually directly connected or synchronized to each other, but there are some HVDC Interconnectors. The Eastern and Western grids are connected with 1.32 GW.
Synchronverters or virtual synchronous generators are inverters which mimic synchronous generators (SG) to provide "synthetic inertia" for ancillary services in electric power systems. Inertia is a property of standard synchronous generators associated with the rotating physical mass of the system spinning at a frequency proportional to the electricity being generated. Inertia has implications towards grid stability as work is required to alter the kinetic energy of the spinning physical mass and therefore opposes changes in grid frequency. Inverter-based generation inherently lacks this property as the waveform is being created artificially via power electronics.
References
- ↑ Vaughn (2007-12-21). "IEEE SCC21 1547 Home Page". IEEE. Retrieved 2008-01-26.
- ↑ Thomas Basso and N. Richard Friedman (November 2003). "IEEE 1547 National Standard for Interconnecting Distributed Generation: How Could It Help My Facility?" (PDF). Distributed Energy. Retrieved 2011-08-28.
- ↑ E. Grebe, D. Klaar; et al. (April 2004). "Final Report of the Investigation Committee on the 28 September 2003 Blackout in Italy" (PDF). Brussels: UCTE . Retrieved 2011-08-28. Please compare with Chapter 6.3.5 and 6.4.1: "For instance, due to its significant penetration level, the effect of the distributed generation may no longer be neglected and appropriate technical requirements need to be defined." p. 94
- ↑ Letter, 18 July 2011 from Mr. Dobbeni, President of ENTSO-E to Mr Oettinger, European Commissioner for Energy
- ↑ "Energy Policy Act of 2005 SEC 1254" (PDF). August 5, 2005. Archived from the original (PDF) on December 1, 2007. Retrieved 2008-01-26.