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== Phasor networks ==
== Phasor networks ==
A phasor network consists of phasor measurement units (PMUs) dispersed throughout the electricity system, Phasor Data Concentrators (PDC) to collect the information and a [[SCADA|Supervisory Control And Data Acquisition]] (SCADA) system at the central control facility. Such a network is used in Wide Area Measurement Systems (WAMS), the first of which was begun in 2000 by the [[Bonneville Power Administration]] <ref>{{cite web
A phasor network consists of phasor measurement units (PMUs) dispersed throughout the electricity system, [[Phasor Data Concentrator|Phasor Data Concentrators (PDC)]] to collect the information and a [[SCADA|Supervisory Control And Data Acquisition]] (SCADA) system at the central control facility. Such a network is used in Wide Area Measurement Systems (WAMS), the first of which was begun in 2000 by the [[Bonneville Power Administration]] <ref>{{cite web
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Revision as of 08:32, 13 January 2011

Using a PMU, it is simple to detect abnormal waveform shapes. A waveform shape described mathematically is called a phasor.

A phasor measurement unit (PMU) measures the electrical waves on an electricity grid to determine the health of the system. In power engineering, these are also commonly referred to as synchrophasors and are considered one of the most important measuring devices in the future of power systems.[1] A PMU can be a dedicated device, or the PMU function can be incorporated into a protective relay or other device.[2]

Technical overview

A phasor is a complex number that represents both the magnitude and phase angle of the sine waves found in electricity. Phasor measurements that occur at the same time are called "synchrophasors", as are the PMU devices that allow their measurement. In typical applications phasor measurement units are sampled from widely dispersed locations in the power system network and synchronized from the common time source of a global positioning system (GPS) radio clock. Synchrophasor technology provides a tool for system operators and planners to measure the state of the electrical system and manage power quality. Synchrophasors measure voltages and currents at diverse locations on a power grid and can output accurately time-stamped voltage and current phasors. Because these phasors are truly synchronized, synchronized comparison of two quantities is possible, in real time. These comparisons can be used to assess system conditions.

The technology has the potential to change the economics of power delivery by allowing increased power flow over existing lines. Synchrophasor data could be used to allow power flow up to a line's dynamic limit instead of to its worst-case limit.

History

In 1893, Charles Proteus Steinmetz presented a paper on simplified mathematical description of the waveforms of alternating electricity. Steinmetz called his representation a phasor.[3] With the invention of phasor measurement units (PMU) in 1988 by Dr. Arun G. Phadke and Dr. James S. Thorp at Virginia Tech, Steinmetz’s technique of phasor calculation evolved into the calculation of real time phasor measurements that are synchronized to an absolute time reference provided by the Global Positioning System. Early prototypes of the PMU were built at Virginia Tech, and Macrodyne built the first PMU (model 1620) in 1992.[4]

Phasor networks

A phasor network consists of phasor measurement units (PMUs) dispersed throughout the electricity system, Phasor Data Concentrators (PDC) to collect the information and a Supervisory Control And Data Acquisition (SCADA) system at the central control facility. Such a network is used in Wide Area Measurement Systems (WAMS), the first of which was begun in 2000 by the Bonneville Power Administration [5]. The complete network requires rapid data transfer within the frequency of sampling of the phasor data. GPS time stamping can provide a theoretical accuracy of synchronization better than 1 microsecond. “Clocks need to be accurate to ± 500 nanoseconds to provide the one microsecond time standard needed by each device performing synchrophasor measurement.” [6] For 60Hz systems, PMUs must deliver between 10 and 30 synchronous reports per second depending on the application. The PDC correlates the data, and controls and monitors the PMUs (from a dozen up to 60).[7] At the central control facility, the SCADA system presents system wide data on all generators and substations in the system every 2 to 10 seconds. PMUs often use phone lines to connect to PDC, which then send data to the SCADA and/or Wide Area Measurement System (WAMS) server.[8]

PMUs from multiple vendors can yield inaccurate readings. In one test, readings differed by 47 microseconds- or a difference of 1 degree of at 60Hz- an unacceptable variance.[9] China's solution to the problem was to build all its own PMUs adhering to its own specifications and standards so there would be no multi-vendor source of conflicts, standards, protocols, or performance characteristics.[10]

Implementations

  • The Bonneville Power Administration (BPA) is the first utility to implement comprehensive adoption of synchrophasors in its wide-area monitoring system. Today there are several implementations underway.
  • The FNET project operated by Virginia Tech and the University of Tennessee utilizes a network of approximately 80 low-cost, high-precision Frequency Disturbance Recorders to collect syncrophasor data from the U.S. power grid. [1]
  • In 2006, China's Wide Area Monitoring Systems (WAMS) for its 6 grids had 300 PMUs installed mainly at 500 kV and 330 kV substations and power plants. By 2012, China plans to have PMUs at all 500kV substations and all powerplants of 300MW and above. Since 2002, China has built its own PMUs to its own national standard. One type has higher sampling rates than typical and is used in power plants to measure rotor angle of the generator, reporting excitation voltage, excitation current, valve position, and output of the power system stabilizer (PSS). All PMUs are connected via private network, and samples are received within 40 ms on average.[10]
  • The North American Synchrophasor Initiative (NASPI), previously known as The Eastern Interconnect Phasor Project (EIPP), has over 120 connected phasor measurement units collecting data into a "Super Phasor Data Concentrator" system centered at Tennessee Valley Authority (TVA). This data concentration system is now an open source project known as the openPDC.
  • The DOE has sponsored several related research projects, including GridStat [2] at Washington State University.

Applications

  1. Power system automation, as in smart grids
  2. Load shedding and other load control techniques such as demand response mechanisms to manage a power system. (i.e. Directing power where it is needed in real-time)
  3. Increase the reliability of the power grid by detecting faults early, allowing for isolation of operative system, and the prevention of power outages.
  4. Increase power quality by precise analysis and automated correction of sources of system degradation.
  5. Wide Area measurement and control, in very wide area super grids, regional transmission networks, and local distribution grids.

Standards

The IEEE 1344 standard for synchrophasors was completed in 1995, and reaffirmed in 2001. In 2005, it was replaced by IEEE Standard C37.118-2005, which was a complete revision and dealt with issues concerning use of PMUs in electric power systems. The specification describes standards for measurement, the method of quantifying the measurements, testing & certification requirements for verifying accuracy, and data transmission format and protocol for real-time data communication.[8] The standard is not yet comprehensive- it does not attempt to address all factors that PMUs can detect in power system dynamic activity.[7]

Other standards used with PMU interfacing:

  • OPC-DA / OPC-HDA - A Microsoft Windows based interface protocol that is currently being generalized to use XML and run on non Windows computers.
  • IEC 61850 a standard for electrical substation automation
  • BPA PDCStream - a variant of IEEE 1344 used by the Bonneville Power Administration (BPA) PDCs and user interface software.[7]

See also

References

  1. ^ Yilu Liu, Lamine Mili, Jaime De La Ree, Reynaldo Francisco Nuqui, Reynaldo Francisco Nuqui (2001-07-12). "State Estimation and Voltage Security Monitoring Using Synchronized Phasor Measurement" (pdf). Research paper from work sponsored by American Electric Power, ABB Power T&D Company, and Tennessee Valley Authority. Virginia Polytechnic Institute and State University. Retrieved 2008-12-01. "Simulations and field experiences suggest that PMUs can revolutionize the way power systems are monitored and controlled. However, it is perceived that costs and communication links will affect the number of PMUs to be installed in any power system." {{cite journal}}: Unknown parameter |laysummary= ignored (help); line feed character in |journal= at position 47 (help)CS1 maint: multiple names: authors list (link)
  2. ^ KEMA, Inc. (November 2006). "Substation Communications: Enabler of Automation / An Assessment of Communications Technologies". UTC - United Telecom Council: 3–40. {{cite journal}}: Check |authorlink= value (help); Cite journal requires |journal= (help)
  3. ^ Charles Proteus Steinmetz (1893). "Complex Quantities and Their Use in Electrical Engineering". Proceedings of the International Electrical Congress, Chicago. Chicago, Illinois 1893 conference of the AIEE: American Institute of Electrical Engineers Proceedings: 33–74.{{cite journal}}: CS1 maint: location (link)
  4. ^ Phadke, A.G. (Virginia Polytechnic Institute and State University) (2002-10-10). "Synchronized phasor measurements-a historical overview" (pdf). Transmission and Distribution Conference and Exhibition 2002: Asia Pacific. IEEE/PES. 1. Institute of Electrical and Electronics Engineers (IEEE): 476. doi:10.1109/TDC.2002.1178427. Retrieved 2008-11-27.
  5. ^ "Gridwise History: How did GridWise start?". Pacific Northwest National Laboratory. 2007-10-30. Retrieved 2008-12-03.
  6. ^ KEMA, Inc. (November 2006). "Substation Communications: Enabler of Automation / An Assessment of Communications Technologies". UTC - United Telecom Council: 3–54. {{cite journal}}: Check |authorlink= value (help); Cite journal requires |journal= (help)
  7. ^ a b c Jim Y. Cai (2005). "Current Status and Experience of WAMS- Implementation in North America" (pdf). Transmission and Distribution Conference and Exhibition: Asia and Pacific, 2005 IEEE/PES. Institute of Electrical and Electronics Engineers (IEEE): 3. doi:10.1109/TDC.2005.1546889. Retrieved 2008-12-06. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help); Unknown parameter |laysummary= ignored (help) Cite error: The named reference "WAMS-1" was defined multiple times with different content (see the help page).
  8. ^ a b Pei Zhang, J. Chen, M. Shao (2007-10). "Phasor Measurement Unit (PMU) Implementation and Applications (DOCID 1015511)" (pdf). Electric Power Research Institute (EPRI). Retrieved 2008-11-27. {{cite journal}}: Check date values in: |date= (help); Cite journal requires |journal= (help)CS1 maint: multiple names: authors list (link)
  9. ^ A. P. Meliopoulos, Vahid Madani, Damir Novosel, George Cokkinides; et al. (2007-10). "Synchrophasor Measurement Accuracy Characterization" (pdf). North American SynchroPhasor Initiative Performance & Standards Task Team. Consortium for Electric Reliability Technology Solutions. Retrieved 2008-11-27. {{cite journal}}: Check date values in: |date= (help); Explicit use of et al. in: |author= (help)CS1 maint: multiple names: authors list (link)
  10. ^ a b Qixun Yang, Board Chairman, Beijing Sifang Automation Co. Ltd., China and .Bi Tianshu, Professor, North China Electric Power University, China. (2001-06-24). "WAMS Implementation in China and the Challenges for Bulk Power System Protection" (pdf). Panel Session: Developments in Power Generation and Transmission INFRASTRUCTURES IN CHINA, IEEE 2007 General Meeting, Tampa, FL, USA, 24–28 June 2007 Electric Power, ABB Power T&D Company, and Tennessee Valley Authority. Institute of Electrical and Electronics Engineers. Retrieved 2008-12-01. {{cite journal}}: line feed character in |journal= at position 65 (help)CS1 maint: multiple names: authors list (link)
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