Utility frequency

The waveform of 230 volt, 50 Hz compared with 110 V, 60 Hz

The utility frequency, (power) line frequency (American English) or mains frequency (British English) is the nominal frequency of the oscillations of alternating current (AC) in an electric power 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 power around the world.

During the development of commercial electric power systems in the late 19th and early 20th centuries, many different frequencies (and voltages) had been used. Large investment in equipment at one frequency made standardization a slow process. However, as of the turn of the 21st century, places that now use the 50 Hz frequency tend to use 220–240 V, and those that now use 60 Hz tend to use 100–127 V. Both frequencies coexist today (Japan uses both) with no great technical reason to prefer one over the other[1] and no apparent desire for complete worldwide standardization.

Unless specified by the manufacturer to operate on both 50 and 60 Hz, appliances may not operate efficiently or even safely if used on anything other than the intended frequency.

In practice, the exact frequency of the grid varies around the nominal frequency, reducing when the grid is heavily loaded, and speeding up when lightly loaded. However, most utilities will adjust the frequency of the grid over the course of the day to ensure a constant number of cycles occur. This is used by some clocks to accurately maintain their time.

Operating factors

Several factors influence the choice of frequency in an AC system.[2] Lighting, motors, transformers, generators and transmission lines all have characteristics which depend on the power frequency. All of these factors interact and make selection of a power frequency a matter of considerable importance. The best frequency is a compromise between contradictory requirements.

In the late 19th century, designers would pick a relatively high frequency for systems featuring transformers and arc lights, so as to economize on transformer materials, but would pick a lower frequency for systems with long transmission lines or feeding primarily motor loads or rotary converters for producing direct current. When large central generating stations became practical, the choice of frequency was made based on the nature of the intended load. Eventually improvements in machine design allowed a single frequency to be used both for lighting and motor loads. A unified system improved the economics of electricity production, since system load was more uniform during the course of a day.

Lighting

The first applications of commercial electric power were incandescent lighting and commutator-type electric motors. Both devices operate well on DC, but DC could not be easily changed in voltage, and was generally only produced at the required utilization voltage.

If an incandescent lamp is operated on a low-frequency current, the filament cools on each half-cycle of the alternating current, leading to perceptible change in brightness and flicker of the lamps; the effect is more pronounced with arc lamps, and the later mercury-vapor and fluorescent lamps. Open arc lamps made an audible buzz on alternating current, leading to experiments with high-frequency alternators to raise the sound above the range of human hearing.

Rotating machines

Commutator-type motors do not operate well on high-frequency AC, because the rapid changes of current are opposed by the inductance of the motor field. Though commutator-type universal motors are common in AC household appliances and power tools, they are small motors, less than 1 kW. The induction motor was found to work well on frequencies around 50 to 60 Hz, but with the materials available in the 1890s would not work well at a frequency of, say, 133 Hz. There is a fixed relationship between the number of magnetic poles in the induction motor field, the frequency of the alternating current, and the rotation speed; so, a given standard speed limits the choice of frequency (and the reverse). Once AC electric motors became common, it was important to standardize frequency for compatibility with the customer's equipment.

Generators operated by slow-speed reciprocating engines will produce lower frequencies, for a given number of poles, than those operated by, for example, a high-speed steam turbine. For very slow prime mover speeds, it would be costly to build a generator with enough poles to provide a high AC frequency. As well, synchronizing two generators to the same speed was found to be easier at lower speeds. While belt drives were common as a way to increase speed of slow engines, in very large ratings (thousands of kilowatts) these were expensive, inefficient and unreliable. After about 1906, generators driven directly by steam turbines favored higher frequencies. The steadier rotation speed of high-speed machines allowed for satisfactory operation of commutators in rotary converters.[2] The synchronous speed N in RPM is calculated using the formula,

N = 120 f P {\displaystyle N={\frac {120f}{P}}\,}

where f is the frequency in Hertz and P is the number of poles.

Synchronous speeds of AC motors for some current and historical utility frequencies
Poles RPM at 133​1 Hz RPM at 60 Hz RPM at 50 Hz RPM at 40 Hz RPM at 25 Hz RPM at 16​2 Hz
2 8,000 3,600 3,000 2,400 1,500 1,000
4 4,000 1,800 1,500 1,200 750 500
6 2,666.7 1,200 1,000 800 500 333.3
8 2,000 900 750 600 375 250
10 1,600 720 600 480 300 200
12 1,333.3 600 500 400 250 166.7
14 1142.9 514.3 428.6 342.8 214.3 142.9
16 1,000 450 375 300 187.5 125
18 888.9 400 333​1 266​2 166​2 111.1
20 800 360 300 240 150 100

Direct-current power was not entirely displaced by alternating current and was useful in railway and electrochemical processes. Prior to the development of mercury arc valve rectifiers, rotary converters were used to produce DC power from AC. Like other commutator-type machines, these worked better with lower frequencies.

Transmission and transformers

With AC, transformers can be used to step down high transmission voltages to lower customer utilization voltage. The transformer is effectively a voltage conversion device with no moving parts and requiring little maintenance. The use of AC eliminated the need for spinning DC voltage conversion motor-generators that require regular maintenance and monitoring.

Since, for a given power level, the dimensions of a transformer are roughly inversely proportional to frequency, a system with many transformers would be more economical at a higher frequency.

Electric power transmission over long lines favors lower frequencies. The effects of the distributed capacitance and inductance of the line are less at low frequency.

System interconnection

Generators can only be interconnected to operate in parallel if they are of the same frequency and wave-shape. By standardizing the frequency used, generators in a geographic area can be interconnected in a grid, providing reliability and cost savings.

History
Japan's utility frequencies are 50 Hz and 60 Hz

Many different power frequencies were used in the 19th century.[3]

Very early isolated AC generating schemes used arbitrary frequencies based on convenience for steam engine, water turbine and electrical generator design. Frequencies between 16⅔ Hz and 133⅓ Hz were used on different systems. For example, the city of Coventry, England, in 1895 had a unique 87 Hz single-phase distribution system that was in use until 1906.[4] The proliferation of frequencies grew out of the rapid development of electrical machines in the period 1880 through 1900.

In the early incandescent lighting period, single-phase AC was common and typical generators were 8-pole machines operated at 2,000 RPM, giving a frequency of 133 hertz.

Though many theories exist, and quite a few entertaining urban legends, there is little certitude in the details of the history of 60 Hz vs. 50 Hz.

The German company AEG (descended from a company founded by Edison in Germany) built the first German generating facility to run at 50 Hz. At the time, AEG had a virtual monopoly and their standard spread to the rest of Europe. After observing flicker of lamps operated by the 40 Hz power transmitted by the Lauffen-Frankfurt link in 1891, AEG raised their standard frequency to 50 Hz in 1891.[5]

Westinghouse Electric decided to standardize on a higher frequency to permit operation of both electric lighting and induction motors on the same generating system. Although 50 Hz was suitable for both, in 1890 Westinghouse considered that existing arc-lighting equipment operated slightly better on 60 Hz, and so that frequency was chosen.[5] The operation of Tesla's induction motor, licensed by Westinghouse in 1888, required a lower frequency than the 133 Hz common for lighting systems at that time. In 1893 General Electric Corporation, which was affiliated with AEG in Germany, built a generating project at Mill Creek, California using 50 Hz, but changed to 60 Hz a year later to maintain market share with the Westinghouse standard.

25 Hz origins

The first generators at the Niagara Falls project, built by Westinghouse in 1895, were 25 Hz, because the turbine speed had already been set before alternating current power transmission had been definitively selected. Westinghouse would have selected a low frequency of 30 Hz to drive motor loads, but the turbines for the project had already been specified at 250 RPM. The machines could have been made to deliver 16⅔ Hz power suitable for heavy commutator-type motors, but the Westinghouse company objected that this would be undesirable for lighting and suggested 33⅓ Hz. Eventually a compromise of 25 Hz, with 12-pole 250 RPM generators, was chosen.[2] Because the Niagara project was so influential on electric power systems design, 25 Hz prevailed as the North American standard for low-frequency AC.

40 Hz origins

A General Electric study concluded that 40 Hz would have been a good compromise between lighting, motor, and transmission needs, given the materials and equipment available in the first quarter of the 20th century. Several 40 Hz systems were built. The Lauffen-Frankfurt demonstration used 40 Hz to transmit power 175 km in 1891. A large interconnected 40 Hz network existed in north-east England (the Newcastle-upon-Tyne Electric Supply Company, NESCO) until the advent of the National Grid (UK) in the late 1920s, and projects in Italy used 42 Hz.[6] The oldest continuously operating commercial hydroelectric power station in the United States, Mechanicville Hydroelectric Plant, still produces electric power at 40 Hz and supplies power to the local 60 Hz transmission system through frequency changers. Industrial plants and mines in North America and Australia sometimes were built with 40 Hz electrical systems which were maintained until too uneconomic to continue. Although frequencies near 40 Hz found much commercial use, these were bypassed by standardized frequencies of 25, 50 and 60 Hz preferred by higher volume equipment manufacturers.

The Ganz Company of Hungary had standardized on 5000 alternations per minute (41​2 Hz) for their products, so Ganz clients had 41​2 Hz systems that in some cases ran for many years.[7]

Standardization
Worldwide electrical voltage and frequency

In the early days of electrification, so many frequencies were used that no one value prevailed (London in 1918 had ten different frequencies). As the 20th century continued, more power was produced at 60 Hz (North America) or 50 Hz (Europe and most of Asia). Standardization allowed international trade in electrical equipment. Much later, the use of standard frequencies allowed interconnection of power grids. It wasn't until after World War II with the advent of affordable electrical consumer goods that more uniform standards were enacted.

In Britain, a standard frequency of 50 Hz was declared as early as 1904, but significant development continued at other frequencies.[8] The implementation of the National Grid starting in 1926 compelled the standardization of frequencies among the many interconnected electrical service providers. The 50 Hz standard was completely established only after World War II.

By about 1900, European manufacturers had mostly standardized on 50 Hz for new installations. The German Verband der Elektrotechnik (VDE), in the first standard for electrical machines and transformers in 1902, recommended 25 Hz and 50 Hz as standard frequencies. VDE did not see much application of 25 Hz, and dropped it from the 1914 edition of the standard. Remnant installations at other frequencies persisted until well after the Second World War.[7]

Because of the cost of conversion, some parts of the distribution system may continue to operate on original frequencies even after a new frequency is chosen. 25 Hz power was used in Ontario, Quebec, the northern United States, and for railway electrification. In the 1950s, many 25 Hz systems, from the generators right through to household appliances, were converted and standardized. Until 2009, some 25 Hz generators were still in existence at the Sir Adam Beck 1 (these were retrofitted to 60 Hz) and the Rankine generating stations (until its 2009 closure) near Niagara Falls to provide power for large industrial customers who did not want to replace existing equipment; and some 25 Hz motors and a 25 Hz power station exist in New Orleans for floodwater pumps.[9] The 15 kV AC rail networks, used in Germany, Austria, Switzerland, Sweden and Norway, still operate at 16⅔ Hz or 16.7 Hz.

In some cases, where most load was to be railway or motor loads, it was considered economic to generate power at 25 Hz and install rotary converters for 60 Hz distribution.[10] Converters for production of DC from alternating current were available in larger sizes and were more efficient at 25 Hz compared with 60 Hz. Remnant fragments of older systems may be tied to the standard frequency system via a rotary converter or static inverter frequency changer. These allow energy to be interchanged between two power networks at different frequencies, but the systems are large, costly, and waste some energy in operation.

Rotating-machine frequency changers used to convert between 25 Hz and 60 Hz systems were awkward to design; a 60 Hz machine with 24 poles would turn at the same speed as a 25 Hz machine with 10 poles, making the machines large, slow-speed and expensive. A ratio of 60/30 would have simplified these designs, but the installed base at 25 Hz was too large to be economically opposed.

In the United States, Southern California Edison had standardized on 50 Hz.[11] Much of Southern California operated on 50 Hz and did not completely change frequency of their generators and customer equipment to 60 Hz until around 1948. Some projects by the Au Sable Electric Company used 30 Hz at transmission voltages up to 110,000 volts in 1914.[12]

Initially in Brazil, electric machinery were imported from Europe and United States, implying the country had both 50 Hz and 60 Hz standards according to each region. In 1938, the federal government made a law, Decreto-Lei 852, intended to bring the whole country under 50 Hz within eight years. The law didn't work, and in the early 1960s it was decided that Brazil would be unified under 60 Hz standard, because most developed and industrialized areas used 60 Hz; and a new law Lei 4.454 was declared in 1964. Brazil underwent a frequency conversion program to 60 Hz that was not completed until 1978.[13]

In Mexico, areas operating on 50 Hz grid were converted during the 1970s, uniting the country under 60 Hz.[14]

In Japan, the western part of the country (Nagoya and west) uses 60 Hz and the eastern part (Tokyo and east) uses 50 Hz. This originates in the first purchases of generators from AEG in 1895, installed for Tokyo, and General Electric in 1896, installed in Osaka. The boundary between the two regions contains four back-to-back HVDC substations which convert the frequency; these are Shin Shinano, Sakuma Dam, Minami-Fukumitsu, and the Higashi-Shimizu Frequency Converter.

Utility frequencies in North America in 1897[15]

Hz Description
140 Wood arc-lighting dynamo
133 Stanley-Kelly Company
125 General Electric single-phase
66.7 Stanley-Kelly company
62.5 General Electric "monocyclic"
60 Many manufacturers, becoming "increasingly common" in 1897
58.3 General Electric Lachine Rapids
40 General Electric
33 General Electric at Portland Oregon for rotary converters
27 Crocker-Wheeler for calcium carbide furnaces
25 Westinghouse Niagara Falls 2-phase—for operating motors

Utility frequencies in Europe to 1900[7]

Hz Description
133 Single-phase lighting systems, UK and Europe
125 Single-phase lighting system, UK and Europe
83.3 Single phase, Ferranti UK, Debtford Power Station, London
70 Single-phase lighting, Germany 1891
65.3 BBC Bellinzona
60 Single phase lighting, Germany, 1891, 1893
50 AEG, Oerlikon, and other manufacturers, eventual standard
48 BBC Kilwangen generating station,
46 Rome, Geneva 1900
45​1 Municipal power station, Frankfurt am Main, 1893
42 Ganz customers, also Germany 1898
41​2 Ganz Company, Hungary
40 Lauffen am Neckar, hydroelectric, 1891, to 1925
38.6 BBC Arlen
25 Single phase lighting, Germany 1897

Even by the middle of the 20th century, utility frequencies were still not entirely standardized at the now-common 50 Hz or 60 Hz. In 1946, a reference manual for designers of radio equipment[16] listed the following now obsolete frequencies as in use. Many of these regions also had 50 cycle, 60 cycle or direct current supplies.

Frequencies in use in 1946 (as well as 50 Hz and 60 Hz)

Hz Region
25 Canada (Southern Ontario), Panama Canal Zone(*), France, Germany, Sweden, UK, China, Hawaii, India, Manchuria
40 Jamaica, Belgium, Switzerland, UK, Federated Malay States, Egypt, West Australia(*)
42 Czechoslovakia, Hungary, Italy, Monaco(*), Portugal, Romania, Yugoslavia, Libya (Tripoli)
43 Argentina
45 Italy, Libya (Tripoli)
76 Gibraltar(*)
100 Malta(*), British East Africa

Where regions are marked (*), this is the only utility frequency shown for that region.

Railways

Other power frequencies are still used. Germany, Austria, Switzerland, Sweden and Norway use traction power networks for railways, distributing single-phase AC at 16⅔ Hz or 16.7 Hz.[17] A frequency of 25 Hz is used for the Austrian Mariazell Railway, as well as Amtrak and SEPTA's traction power systems in the United States. Other AC railway systems are energized at the local commercial power frequency, 50 Hz or 60 Hz.

Traction power may be derived from commercial power supplies by frequency converters, or in some cases may be produced by dedicated traction powerstations. In the 19th Century, frequencies as low as 8 Hz were contemplated for operation of electric railways with commutator motors.[2] Some outlets in trains carry the correct voltage, but using the original train network frequency like 16⅔ Hz or 16.7 Hz.

400 Hz

Power frequencies as high as 400 Hz are used in aircraft, spacecraft, submarines, server rooms for computer power,[18] military equipment, and hand-held machine tools. Such high frequencies cannot be economically transmitted long distances; the increased frequency greatly increases series impedance due to the inductance of transmission lines, making power transmission difficult. Consequently, 400 Hz power systems are usually confined to a building or vehicle.

Transformers, for example, can be made smaller because the magnetic core can be much smaller for the same power level. Induction motors turn at a speed proportional to frequency, so a high frequency power supply allows more power to be obtained for the same motor volume and mass. Transformers and motors for 400 Hz are much smaller and lighter than at 50 or 60 Hz, which is an advantage in aircraft and ships. A United States military standard MIL-STD-704 exists for aircraft use of 400 Hz power.

StabilityTime error correction (TEC)

Regulation of power system frequency for timekeeping accuracy was not commonplace until after 1926 with Laurens Hammond's invention of the electric clock driven by a synchronous motor. During the 1920s, Hammond gave away hundreds of such clocks to power station owners in the U.S. and Canada as incentive to maintain a steady 60-cycle frequency, thus rendering his inexpensive clock uniquely practical in any business or home in North America. Developed in 1933, The Hammond Organ uses a synchronous AC clock motor to maintain correct speed of its internal 'tone wheel' generator, thus keeping all notes pitch perfect, based on power-line frequency stability.

Today, AC-power network operators regulate the daily average frequency so that clocks stay within a few seconds of correct time. In practice the nominal frequency is raised or lowered by a specific percentage to maintain synchronization. Over the course of a day, the average frequency is maintained at the nominal value within a few hundred parts per million.[19] In the synchronous grid of Continental Europe, the deviation between network phase time and UTC (based on International Atomic Time) is calculated at 08:00 each day in a control center in Switzerland. The target frequency is then adjusted by up to ±0.01 Hz (±0.02%) from 50 Hz as needed, to ensure a long-term frequency average of exactly 50 Hz × 60 s/min × 60 min/h × 24 h/d = 4320000 cycles per day.[20] In North America, whenever the error exceeds 10 seconds for the east, 3 seconds for Texas, or 2 seconds for the west, a correction of ±0.02 Hz (0.033%) is applied. Time error corrections start and end either on the hour or on the half-hour.[21][22] Efforts to remove the TEC in North America are described at electric clock.

Real-time frequency meters for power generation in the United Kingdom are available online – an official National Grid one, and an unofficial one maintained by Dynamic Demand.[23][24] Real-time frequency data of the synchronous grid of Continental Europe is available on websites such as mainsfrequency.com and gridfrequency.eu. The Frequency Monitoring Network (FNET) at the University of Tennessee measures the frequency of the interconnections within the North American power grid, as well as in several other parts of the world. These measurements are displayed on the FNET website.[25]

US Regulations

In the United States, the Federal Energy Regulatory Commission made Time Error Correction mandatory in 2009.[26] In 2011, The North American Electric Reliability Corporation (NERC) discussed a proposed experiment that would relax frequency regulation requirements[27] for electrical grids which would reduce the long-term accuracy of clocks and other devices that use the 60 Hz grid frequency as a time base.[28]

Frequency and load

The primary reason for accurate frequency control is to allow the flow of alternating current power from multiple generators through the network to be controlled. The trend in system frequency is a measure of mismatch between demand and generation, and is a necessary parameter for load control in interconnected systems.

Frequency of the system will vary as load and generation change. Increasing the mechanical input power to a synchronous generator will not greatly affect the system frequency, but will produce more electric power from that unit. During a severe overload caused by tripping or failure of generators or transmission lines the power system frequency will decline, due to an imbalance of load versus generation. Loss of an interconnection, while exporting power (relative to system total generation) will cause system frequency to rise. Automatic generation control (AGC) is used to maintain scheduled frequency and interchange power flows. Control systems in power stations detect changes in the network-wide frequency and adjust mechanical power input to generators back to their target frequency. This counteracting usually takes a few tens of seconds due to the large rotating masses involved. Temporary frequency changes are an unavoidable consequence of changing demand. Exceptional or rapidly changing mains frequency is often a sign that an electricity distribution network is operating near its capacity limits, dramatic examples of which can sometimes be observed shortly before major outages. Large solar farms can reduce their average output and use the extra capacity to assist in providing grid regulation; response of solar inverters is faster than generators, because they have no rotating mass.[29][30]

Frequency protective relays on the power system network sense the decline of frequency and automatically initiate load shedding or tripping of interconnection lines, to preserve the operation of at least part of the network. Small frequency deviations (i.e.- 0.5 Hz on a 50 Hz or 60 Hz network) will result in automatic load shedding or other control actions to restore system frequency.

Smaller power systems, not extensively interconnected with many generators and loads, will not maintain frequency with the same degree of accuracy. Where system frequency is not tightly regulated during heavy load periods, the system operators may allow system frequency to rise during periods of light load, to maintain a daily average frequency of acceptable accuracy.[31][32] Portable generators, not connected to a utility system, need not tightly regulate their frequency, because typical loads are insensitive to small frequency deviations.

Load-frequency control

Load-frequency control (LFC) is a type of integral control that restores the system frequency and power flows to adjacent areas back to their values before a change in load. The power transfer between different areas of a system is known as "net tie-line power".

The general control algorithm for LFC was developed by Nathan Cohn in 1971.[33] The algorithm involves defining the term "area control error" (ACE), which is the sum of the net tie-line power error and the product of the frequency error with a frequency bias constant. When the area control error is reduced to zero, the control algorithm has returned the frequency and tie-line power errors to zero.[34]

Audible noise and interference

AC-powered appliances can give off a characteristic hum, often called "mains hum", at the multiples of the frequencies of AC power that they use (see Magnetostriction). It is usually produced by motor and transformer core laminations vibrating in time with the magnetic field. This hum can also appear in audio systems, where the power supply filter or signal shielding of an amplifier is not adequate.

50 Hz power hum
60 Hz power hum
400 Hz power hum

Most countries chose their television vertical synchronization rate to approximate the local mains supply frequency. This helped to prevent power line hum and magnetic interference from causing visible beat frequencies in the displayed picture of analogue receivers.

Another use of this side effect has resulted in its use as a forensic tool. When a recording is made that captures audio near an AC appliance or socket, the hum is also inadvertently recorded. The peaks of the hum repeat every AC cycle (every 20 ms for 50 Hz AC, or every 16.67 ms for 60 Hz AC). Any edit of the audio that is not a multiplication of the time between the peaks will distort the regularity, introducing a phase shift. A continuous wavelet transform analysis will show discontinuities that may tell if the audio has been cut.[35]

See also Further reading
  • Furfari, F.A., The Evolution of Power-Line Frequencies 133⅓ to 25 Hz, Industry Applications Magazine, IEEE, Sep/Oct 2000, Volume 6, Issue 5, Pages 12–14, ISSN 1077-2618.
  • Rushmore, D.B., Frequency, AIEE Transactions, Volume 31, 1912, pages 955-983, and discussion on pages 974-978.
  • Blalock, Thomas J., Electrification of a Major Steel Mill - Part II Development of the 25 Hz System, Industry Applications Magazine, IEEE, Sep/Oct 2005, Pages 9–12, ISSN 1077-2618.
References
  1. A.C. Monteith , C.F. Wagner (ed), Electrical Transmission and Distribution Reference Book 4th Edition, Westinghouse Electric Corporation 1950, page 6
  2. B. G. Lamme, The Technical Story of the Frequencies, Transactions AIEE January 1918, reprinted in the Baltimore Amateur Radio Club newsletter The Modulator January -March 2007
  3. Fractional Hz frequencies originated in the 19th century practice that gave frequencies in terms of alternations per minute, instead of alternations (cycles) per second. For example, a machine which produced 8,000 alternations per minute is operating at 133⅓ cycles per second.
  4. Gordon Woodward ,City of Coventry Single and Two Phase Generation and Distribution, retrieved from http://www.iee.org/OnComms/pn/History/HistoryWk_Single_&_2_phase.pdf October 30, 2007
  5. Owen, Edward (1997-11-01). "The Origins of 60-Hz as a Power Frequency" (PDF). Industry Applications Magazine. IEEE. pp. 8, 10, 12–14.
  6. Thomas P. Hughes, Networks of Power: Electrification in Western Society 1880–1930, The Johns Hopkins University Press, Baltimore 1983 ISBN 0-8018-2873-2 pgs. 282-283
  7. Gerhard Neidhofer 50-Hz frequency: how the standard emerged from a European jungle, IEEE Power and Energy Magazine, July/August 2011 pp. 66-81
  8. The Electricity Council, Electricity Supply in the United Kingdom: A Chronology from the beginnings of the industry to 31 December 1985 Fourth Edition, ISBN 0-85188-105-X, page 41
  9. "LaDOTD".
  10. Samuel Insull, Central-Station Electric Service, private printing, Chicago 1915, available on the Internet Archive,page 72
  11. Central Station Engineers of the Westinghouse Electric Corporation, Electrical Transmission and Distribution Reference Book, 4th Ed., Westinghouse Electric Corporation, East Pittsburgh Pennsylvania, 1950, no ISBN
  12. Hughes as above
  13. Atitude Editorial. "Padrões brasileiros".
  14. http://www.cfe.gob.mx/es/LaEmpresa/queescfe/CFEylaelectricidadenMéxico/
  15. Edwin J. Houston and Arthur Kennelly, Recent Types of Dynamo-Electric Machinery, copyright American Technical Book Company 1897, published by P.F. Collier and Sons New York, 1902
  16. H.T. Kohlhaas, ed. (1946). Reference Data for Radio Engineers (PDF) (2nd ed.). New York: Federal Telephone and Radio Corporation. p. 26.
  17. C. Linder (2002), "Umstellung der Sollfrequenz im zentralen Bahnstromnetz von 16 2/3 Hz auf 16,70 Hz (English: Switching the frequency in train electric power supply network from 16 2/3 Hz to 16,70 Hz)", Elektrische Bahnen (in German), Munich: Oldenbourg-Industrieverlag, Book 12, ISSN 0013-5437
  18. Formerly, IBM mainframe computer systems also used 415 Hz power systems within a computer room. Robert B. Hickey,Electrical engineer's portable handbook, page 401
  19. Fink, Donald G.; Beaty, H. Wayne (1978). Standard Handbook for Electrical Engineers (Eleventh ed.). New York: McGraw-Hill. pp. 16–15, 16–16. ISBN 0-07-020974-X.
  20. Entsoe Load Frequency Control and Performance, chapter D.
  21. "Manual Time Error Correction" (PDF). naesb.org. Retrieved 4 April 2018.
  22. Time Error Correction.
  23. "National Grid: Real Time Frequency Data – Last 60 Minutes".
  24. "Dynamic Demand".
  25. fnetpublic.utk.edu
  26. "Western Electricity Coordinating Council Regional Reliability Standard Regarding Automatic Time Error Correction" (PDF). Federal Energy Regulatory Commission. May 21, 2009. Retrieved June 23, 2016.
  27. "Time error correction and reliability (draft)" (PDF). North American Electric Reliability Corporation. Retrieved June 23, 2016.
  28. "Power-grid experiment could confuse clocks - Technology & science - Innovation - NBC News". msnbc.com.
  29. "First Solar Proves That PV Plants Can Rival Frequency Response Services From Natural Gas Peakers". 19 January 2017. Retrieved 20 January 2017.
  30. "USING RENEWABLES TO OPERATE A LOW-CARBON GRID" (PDF). caiso.com. Retrieved 4 April 2018.
  31. Donald G. Fink and H. Wayne Beaty, Standard Handbook for Electrical Engineers, Eleventh Edition,McGraw-Hill, New York, 1978, ISBN 0-07-020974-X, pp. 16–15 thought 16-21
  32. Edward Wilson Kimbark Power System Stability Vol. 1, John Wiley and Sons, New York, 1948 pg. 189
  33. Cohn, N. Control of Generation and Power Flow on Interconnected Systems. New York: Wiley. 1971
  34. Glover, Duncan J. et al. Power System Analysis and Design. 5th Edition. Cengage Learning. 2012. pp. 663-664.
  35. "The hum that helps to fight crime". BBC News.
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Utility frequency

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Utility frequency

The waveform of 230 volt, 50 Hz compared with 110 V, 60 Hz The utility frequency, (power) line frequency (American English) or mains frequency (British English) is the nominal frequency of the oscillations of alternating current (AC) in an electric power 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 power around the world. During the development of commercial electric power systems in the late 19th and early 20th centuries, many different frequencies (and voltages) had been used. Large investment in equipment at one frequency made standardization a slow process. However, as of the turn of the 21st century, places that now use the 50 Hz frequency tend to use 220–240 V, and those that now use 60 Hz tend to use 100–127 V. Both frequencies coexist today (Japan uses both) with no great technical reason to prefer one over the other[ ...more...

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Frequency changer

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Frequency changer

The Sakuma frequency converter station is one of the stations that links Japan's two grids. A frequency changer or frequency converter is an electronic or electromechanical device that converts alternating current (AC) of one frequency to alternating current of another frequency. The device may also change the voltage, but if it does, that is incidental to its principal purpose. Traditionally, these devices were electromechanical machines called a motor-generator set.[1] Also devices with mercury arc rectifiers or vacuum tubes were in use. With the advent of solid state electronics, it has become possible to build completely electronic frequency changers. These devices usually consist of a rectifier stage (producing direct current) which is then inverted to produce AC of the desired frequency. The inverter may use thyristors, IGCTs or IGBTs. If voltage conversion is desired, a transformer will usually be included in either the ac input or output circuitry and this transformer may also provide galvanic isol ...more...

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Solar inverter

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Solar inverter

Internal view of a solar inverter. Note the many large capacitors (blue cylinders), used to store energy briefly and improve the output waveform. A solar inverter or PV inverter, is a type of electrical converter which converts the variable direct current (DC) output of a photovoltaic (PV) solar panel into a utility frequency alternating current (AC) that can be fed into a commercial electrical grid or used by a local, off-grid electrical network. It is a critical balance of system (BOS)–component in a photovoltaic system, allowing the use of ordinary AC-powered equipment. Solar power inverters have special functions adapted for use with photovoltaic arrays, including maximum power point tracking and anti-islanding protection. Classification Simplified schematics of a grid-connected residential photovoltaic power system[1] Solar inverters may be classified into three broad types:[2] Stand-alone inverters, used in isolated systems where the inverter draws its DC energy from batteries charged by ph ...more...

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Wattmeter

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Wattmeter

Wattmeter The wattmeter is an instrument for measuring the electric power (or the supply rate of electrical energy) in watts of any given circuit. Electromagnetic wattmeters are used for measurement of utility frequency and audio frequency power; other types are required for radio frequency measurements. Electrodynamic Early wattmeter on display at the Historic Archive and Museum of Mining in Pachuca, Mexico The traditional analog wattmeter is an electrodynamic instrument. The device consists of a pair of fixed coils, known as current coils, and a movable coil known as the potential coil. The current coils are connected in series with the circuit, while the potential coil is connected in parallel. Also, on analog wattmeters, the potential coil carries a needle that moves over a scale to indicate the measurement. A current flowing through the current coil generates an electromagnetic field around the coil. The strength of this field is proportional to the line current and in phase with it. The poten ...more...

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Utility (disambiguation)

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Utility (disambiguation)

Look up utility in Wiktionary, the free dictionary. Utility is a measure of the happiness or satisfaction gained from a good or service in economics and game theory. Utility or Utilities may also refer to: Public utility, an organization that maintains the infrastructure for a public service, or the services themselves Utility (patent), one of the requirements for patentability in Canadian and United States patent laws Utility (car), a term used in Australia and New Zealand to refer to a pickup truck or coupe utility vehicle ("ute") Utilities (film), a 1981 movie starring Robert Hays Marine Corps Combat Utility Uniform, often abbreviated to "Utilities", the battledress uniform of the United States Marine Corps Utility, a software program designed for a specific task: see List of utility software See also Utility player, a baseball player who plays more than one position regularly, usually in a reserve capacity Utility model, an intellectual property right to protect inventions Utility f ...more...



Electrical grid

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Electrical grid

General layout of electricity networks. Voltages and depictions of electrical lines are typical for Germany and other European systems. An electrical grid is an interconnected network for delivering electricity from producers to consumers. It consists of generating stations that produce electrical power, high voltage transmission lines that carry power from distant sources to demand centers, and distribution lines that connect individual customers.[1] Power stations may be located near a fuel source, at a dam site, or to take advantage of renewable energy sources, and are often located away from heavily populated areas. The electric power which is generated is stepped up to a higher voltage at which it connects to the electric power transmission net. The bulk power transmission network will move the power long distances, sometimes across international boundaries, until it reaches its wholesale customer (usually the company that owns the local electric power distribution network). On arrival at a substat ...more...

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Induction heating

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Induction heating

Component of Stirling radioisotope generator is heated by induction during testing Induction heating is the process of heating an electrically conducting object (usually a metal) by electromagnetic induction, through heat generated in the object by eddy currents. An induction heater consists of an electromagnet, and an electronic oscillator that passes a high-frequency alternating current (AC) through the electromagnet. The rapidly alternating magnetic field penetrates the object, generating electric currents inside the conductor called eddy currents. The eddy currents flowing through the resistance of the material heat it by Joule heating. In ferromagnetic (and ferrimagnetic) materials like iron, heat may also be generated by magnetic hysteresis losses. The frequency of current used depends on the object size, material type, coupling (between the work coil and the object to be heated) and the penetration depth. An important feature of the induction heating process is that the heat is generated inside the ...more...

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Mains electricity

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Mains electricity

World map showing the percentage of the population in each country with access to mains electricity (as of 2012), a measure of the extent of electrification. Mains electricity (as it is known in the UK; US terms include grid power, wall power, and domestic power) is the general-purpose alternating-current (AC) electric power supply. It is the form of electrical power that is delivered to homes and businesses, and it is the form of electrical power that consumers use when they plug kitchen appliances, televisions and electric lamps into wall sockets. The two principal properties of the electric power supply, voltage and frequency, differ between regions. A voltage of (nominally) 230 V and a frequency of 50 Hz is used in Europe, most of Africa, most of Asia, much of South America and Australia. In North America, the most common combination is 120 V and a frequency of 60 Hz. Other voltages exist, and some countries may have, for example, 230 V but 60 Hz. This is a concern to travellers, since portable applian ...more...

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Frequency-hopping spread spectrum

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Frequency-hopping spread spectrum

Frequency-hopping spread spectrum (FHSS) is a method of transmitting radio signals by rapidly switching a carrier among many frequency channels, using a pseudorandom sequence known to both transmitter and receiver. It is used as a multiple access method in the code division multiple access (CDMA) scheme frequency-hopping code division multiple access (FH-CDMA). Each available frequency band is divided into sub-frequencies. Signals rapidly change ("hop") among these in a predetermined order. Interference at a specific frequency will only affect the signal during that short interval. FHSS can, however, cause interference with adjacent direct-sequence spread spectrum (DSSS) systems. A sub-type of FHSS used in Bluetooth wireless data transfer is adaptive frequency-hopping spread spectrum (AFH). Spread-spectrum A spread-spectrum transmission offers three main advantages over a fixed-frequency transmission: Spread-spectrum signals are highly resistant to narrowband interference. The process of re-collecting a ...more...

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Radio resource management

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High frequency

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High frequency

HF's position in the electromagnetic spectrum. High frequency (HF) is the ITU designation[1] for the range of radio frequency electromagnetic waves (radio waves) between 3 and 30 megahertz (MHz). It is also known as the decameter band or decameter wave as its wavelengths range from one to ten decameters (ten to one hundred metres). Frequencies immediately below HF are denoted medium frequency (MF), while the next band of higher frequencies is known as the very high frequency (VHF) band. The HF band is a major part of the shortwave band of frequencies, so communication at these frequencies is often called shortwave radio. Because radio waves in this band can be reflected back to Earth by the ionosphere layer in the atmosphere – a method known as "skip" or "skywave" propagation – these frequencies are suitable for long-distance communication across intercontinental distances. The band is used by international shortwave broadcasting stations (2.31–25.82 MHz), aviation communication, government time stations, w ...more...

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Electric clock

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Electric clock

Telechron synchronous electric clock manufactured around 1940. By 1940 the synchronous clock became the most common type of clock in the U.S. An electric clock is a clock that is powered by electricity, as opposed to a mechanical clock which is powered by a hanging weight or a mainspring. The term is often applied to the electrically powered mechanical clocks that were used before quartz clocks were introduced in the 1980s. The first experimental electric clocks were constructed around 1840, but they were not widely manufactured until mains electric power became available in the 1890s. In the 1930s the synchronous electric clock replaced mechanical clocks as the most widely used type of clock. Types Electromechanical self-winding clock movement from Switzerland. Electric clocks can operate by several different types of mechanism: Electromechanical clocks These have a traditional mechanical movement, which keeps time with an oscillating pendulum or balance wheel powered through a gear train by a ma ...more...

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Scottish inventions

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Utility station

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Utility station

The term utility station is used to describe fixed radio broadcasters disseminating signals that are not intended for reception by the general public (but such members are not actively prohibited from receiving). Utility stations, as the name suggests, do broadcast signals that have an immediate practical use, by means of analog or usually digital modes; most often utility transmissions are of a "point-to-point" nature, intended for a specific receiving station. Utility stations are most prevalent on shortwave frequencies, though they are not restricted to the shortwave frequencies. Examples of utility station and modes One common use of utility stations is disseminating weather information. Weather information is often broadcast using RTTY and sending synoptic codes, or weather charts are sent using radiofax, which are used by mariners and others. Airports make voice weather broadcasts on HF, known as VOLMET. Some examples include New York Radio, which broadcasts weather information for locations in the eas ...more...

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Radio stations

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Beacon Power

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Beacon Power

Beacon Power is an American limited liability company and wholly owned subsidiary of Rockland Capital LLC specializing in flywheel-based energy storage headquartered in Tyngsboro, Massachusetts. Beacon designs and develops products aimed at utility frequency regulation for power grid operations. The storage systems are designed to help utilities match supply with varying demand by storing excess power in arrays of 2,800-pound (1,300 kg) flywheels at off-peak times for use during peak demand.[5] History Beacon Power was founded in Woburn, Massachusetts in 1997 as a subsidiary of SatCon Technology Corporation, a maker of alternative energy management systems. The company went public in 2000.[6][7][8] In June 2008, Beacon Power opened new headquarters in Tyngsboro, with financing from Massachusetts state agencies. The new facility is intended to support an expansion of the company's operation.[5] In 2009 Beacon received a loan guarantee from the United States Department of Energy (DOE) for $43 million to bui ...more...

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Companies started in 1997

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Mains electricity by country

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Mains electricity by country

Mains electricity by country includes a list of countries and territories, with the plugs, voltages and frequencies they commonly use for providing electrical power to appliances, equipment, and lighting typically found in homes and offices. (For industrial machinery, see Industrial and multiphase power plugs and sockets.) Some countries have different voltage levels for small vs. large appliances, and sometimes different plugs are mandated for different voltage or current levels. Voltage, frequency, and plug type vary widely, but large regions may use common standards. Physical compatibility of receptacles may not ensure compatibility of voltage, frequency, or connection to earth (ground), including plugs and cords. In some areas, older standards may still exist. Foreign enclaves, extraterritorial government installations, or buildings frequented by tourists may support plugs not otherwise used in a country, for the convenience of travellers. Main reference source—IEC World Plugs The International Electrot ...more...

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Islanding

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Islanding

Islanding is the condition in which a distributed generator (DG) continues to power a location even though 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 is going to be violated, 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. A common example of islanding is a distribution feeder that has solar panels attached to it. In the case of a power outage, the solar panels will continue to deliver power as long as irradiance is sufficient. In this case, the circuit detached by the outage becomes an "island". For this reason, solar inverters that are designed to supply power to the grid are generally required to hav ...more...

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Ground loop (electricity)

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Ground loop (electricity)

In an electrical system, a ground loop or earth loop occurs when two points of a circuit both intended to be at ground reference potential have a potential between them.[1] This can be caused, for example, in a signal circuit referenced to ground, if enough current is flowing in the ground to cause two points to be at different potentials. Ground loops are a major cause of noise, hum, and interference in audio, video, and computer systems. Wiring practices that protect against ground loops include ensuring that all vulnerable signal circuits are referenced to one point as ground. The use of differential connections can provide rejections of ground-induced interference. Removal of safety ground connections to equipment in an effort to eliminate ground loops also eliminates the protection the safety ground connection is intended to provide. Ground loop 50 Hz sound Ground loop at 50 Hz captured with audio equipment. Problems playing this file? See media help. Description A ground loop is c ...more...

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Induction furnace

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Induction furnace

An Induction Furnace is an electrical furnace in which the heat is applied by induction heating of metal.[1][2][3] Induction furnace capacities range from less than one kilogram to one hundred tonnes, and are used to melt iron and steel, copper, aluminium, and precious metals. The advantage of the induction furnace is a clean, energy-efficient and well-controllable melting process compared to most other means of metal melting. Most modern foundries use this type of furnace, and now also more iron foundries are replacing cupolas with induction furnaces to melt cast iron, as the former emit lots of dust and other pollutants.[4] Since no arc or combustion is used, the temperature of the material is no higher than required to melt it; this can prevent loss of valuable alloying elements.[5] The one major drawback to induction furnace usage in a foundry is the lack of refining capacity; charge materials must be clean of oxidation products and of a known composition and some alloying elements may be lost due to ...more...

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Industrial furnaces

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Variable-frequency drive

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Variable-frequency drive

Small variable-frequency drive Chassis of above VFD (cover removed) A variable-frequency drive (VFD; also termed adjustable-frequency drive, “variable-voltage/variable-frequency (VVVF) drive”, variable speed drive, AC drive, micro drive or inverter drive) is a type of adjustable-speed drive used in electro-mechanical drive systems to control AC motor speed and torque by varying motor input frequency and voltage.[1][2][3][4] VFDs are used in applications ranging from small appliances to large compressors. About 25% of the world's electrical energy is consumed by electric motors in industrial applications, which can be more efficient when using VFDs in centrifugal load service;[5] however, VFDs' global market penetration for all applications is relatively small. Over the last four decades, power electronics technology has reduced VFD cost and size and has improved performance through advances in semiconductor switching devices, drive topologies, simulation and control techniques, and control hardware ...more...

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GPU-Z

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GPU-Z

GPU-Z is a lightweight utility designed to provide information about video cards and GPUs[2]. The program displays the specifications of the GPU and its memory, and displays temperature, core frequency, memory frequency, GPU load and fan speeds. Features This program allows to view the following information of the video card: Card's name GPU title Technology process Chip area Number of transistors Support for DirectX / Pixel Shader Memory type Amount of memory Memory bandwidth Type of bus Width of the bus Frequency of the GPU (standard / overclocked) Memory clock Driver version BIOS version Sensors[3] GPU core clock[3] GPU memory clock Low GPU Fan speed Downloads GPU real-time See also CPU-Z References "TechPowerUp GPU-Z Download Page". TechPowerUp GPU-Z "Monitor Your GPU on Windows with GPU-Z by TechPowerUp - Windows Experience BlogWindows Experience Blog". blogs.windows.com. Retrieved 2017-06-05. External links Official website ...more...

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Windows-only free software

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Continental U.S. power transmission grid

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Continental U.S. power transmission grid

The two major and three minor NERC interconnections, and the nine NERC Regional Reliability Councils. The electric power transmission grid of the contiguous United States consists of 120,000 miles (190,000 km) of lines operated by 500 companies. The electrical grid that powers mainland North America is divided into multiple regions. 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 60 Hz electrical power. The regions are not directly connected or synchronized to each other, but there are some HVDC interconnections. In the United States[1] and Canada,[2] national standards specify that the nominal voltage supplied to the consumer should be 120 V and allow a range of 114 V to 126 V (RMS) (−5% to +5%). Historically 110 V, 115 V and 117 V have been used at different times and places in North America. Mains power is sometimes spoken of as 110 V; ...more...



Utility player

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Utility player

In sport, a utility player is one who can play several positions competently, a sort of jack of all trades. Sports in which the term is often used include football, baseball, rugby union, rugby league, water polo, and softball. The term has gained prominence in all sports due to its use in fantasy leagues, but in rugby and rugby league, it is commonly used by commentators to recognize a player's versatility. Association football For a more comprehensive list, see: Category:Association football utility players In football, like other sports, the utility man is usually a player who can play myriad positions. This will commonly be defence and midfield, sometimes defence and attack. A few outfield players have also made competent substitute goalkeepers, for example Phil Jagielka, Jan Koller (originally trained as a goalkeeper before converting into a striker) and Cosmin Moți.[1] But in the case of goalkeepers playing as outfield players, it is extremely rare. Some may be free kick and penalty specialists (Rog ...more...

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Terminology used in multiple sports

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576i

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576i

SDTV resolution by nation; countries using 576i are in blue. 576i is a standard-definition video mode originally used for broadcast television in most countries of the world where the utility frequency for electric power distribution is 50 Hz. Because of its close association with the color encoding system, it is often referred to as simply PAL, PAL/SECAM or SECAM when compared to its 60 Hz (typically, see PAL-M) NTSC-color-encoded counterpart, 480i. In digital applications it is usually referred to as "576i"; in analogue contexts it is often called "625 lines",[1] and the aspect ratio is usually 4:3 in analogue transmission and 16:9 in digital transmission. The 576 identifies a vertical resolution of 576 lines, and the i identifies it as an interlaced resolution. The field rate, which is 50 Hz, is sometimes included when identifying the video mode, i.e. 576i50; another notation, endorsed by both the International Telecommunication Union in BT.601 and SMPTE in SMPTE 259M, includes the frame rate, as in 576 ...more...

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Electric power distribution

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Electric power distribution

A 50 kVA pole-mounted distribution transformer 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.[1] 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 or 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.[2] History The late 1 ...more...

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Resolver (electrical)

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Resolver (electrical)

A resolver is a type of rotary electrical transformer used for measuring degrees of rotation. It is considered an analog device, and has digital counterparts such as the digital resolver, rotary (or pulse) encoder. Description Concept of rotor excited resolver Rotor excitation and response The most common type of resolver is the brushless transmitter resolver (other types are described at the end). On the outside, this type of resolver may look like a small electrical motor having a stator and rotor. On the inside, the configuration of the wire windings makes it different. The stator portion of the resolver houses three windings: an exciter winding and two two-phase windings (usually labeled "x" and "y") (case of a brushless resolver). The exciter winding is located on the top; it is in fact a coil of a turning (rotary) transformer. This transformer induces current in the rotor without a direct electrical connection, thus there are no wires to the rotor limiting its rotation and no need for brush ...more...

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Transformers (electrical)

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Alternating current

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Alternating current

Alternating current (green curve). The horizontal axis measures time; the vertical, current or voltage. Alternating current (AC) is an electric current which periodically reverses direction, in contrast to direct current (DC) which flows only in one direction. Alternating current is the form in which electric power is delivered to businesses and residences, and it is the form of electrical energy that consumers typically use when they plug kitchen appliances, televisions, fans and electric lamps into a wall socket. A common source of DC power is a battery cell in a flashlight. The abbreviations AC and DC are often used to mean simply alternating and direct, as when they modify current or voltage.[1][2] The usual waveform of alternating current in most electric power circuits is a sine wave. In certain applications, different waveforms are used, such as triangular or square waves. Audio and radio signals carried on electrical wires are also examples of alternating current. These types of alternating current ...more...

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Quartz clock

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Quartz clock

A quartz clock A quartz clock is a clock that uses an electronic oscillator that is regulated by a quartz crystal to keep time. This crystal oscillator creates a signal with very precise frequency, so that quartz clocks are at least an order of magnitude more accurate than mechanical clocks. Generally, some form of digital logic counts the cycles of this signal and provides a numeric time display, usually in units of hours, minutes, and seconds. The first quartz clock was built in 1927 by Warren Marrison and J. W. Horton at Bell Telephone Laboratories. Since the 1980s, when the advent of solid-state digital electronics allowed them to be made compact and inexpensive, quartz timekeepers have become the world's most widely used timekeeping technology, used in most clocks and watches, as well as computers and other appliances that keep time. Explanation First European quartz clock for consumers "Astrochron", Junghans, Schramberg, 1967 (German Clock Museum, Inv. 1995-603) First quartz wristwatch move ...more...

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Horology

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Cardinal utility

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Cardinal utility

A simple example of two cardinal utility functions u (first column) and v (second column) whose values in all circumstances are related by v=2u+3 In economics, a cardinal utility function or scale is a utility index that preserves preference orderings uniquely up to positive affine transformations.[1][2] Two utility indices are related by an affine transformation if for the value u ( x i ) {\displaystyle u(x_{i})} of one index u, occurring at any quantity x i {\displaystyle x_{i}} of the goods bundle being evaluated, the corresponding value v ( x i ) {\displaystyle v(x_{i})} of the other index v satisfies a relationship of the form v ( x i ) = a u ( x i ) + b {\displaystyle v(x_{i})=au(x_{i})+b\!} , for fixed constants a and b. Thus the utility functions themselves are related by v ( x ) = a u ( x ) + b . {\displaystyle v(x)=au(x)+b.} The two indices differ only with respect to scale and origin.[1] Thus if one is concave, so is the other, in whi ...more...

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Transfer switch

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Transfer switch

3-phase transfer switch single-line diagram Intelligent transfer switch A transfer switch is an electrical switch that switches a load between two sources. Some transfer switches are manual, in that an operator effects the transfer by throwing a switch, while others are automatic and trigger when they sense one of the sources has lost or gained power. An Automatic Transfer Switch (ATS) is often installed where a backup generator is located, so that the generator may provide temporary electrical power if the utility source fails. Operation of a transfer switch As well as transferring the load to the backup generator, an ATS may also command the backup generator to start, based on the voltage monitored on the primary supply. The transfer switch isolates the backup generator from the electric utility when the generator is on and providing temporary power. The control capability of a transfer switch may be manual only, or a combination of automatic and manual. The switch transition mode (see below) of a ...more...

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Switches

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Grid GridCase 1535EXP

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Grid GridCase 1535EXP

Grid GridCase 1535EXP is a rugged laptop with a 80386 CPU, an optional 80387 floating point processor and up to 8 Mbyte of DRAM designed for NASA to be used in space. It was first flown into space in December 1992 on the STS-53 for use of the HERCULES geolocation device. The power input is 100-240 V AC 50/60/400 Hz, 80 W. The 400 Hz utility frequency is common on airplanes and submarines. See also Switched-mode power supply applications - Use of 400 Hz powergrid. References "DAVES OLD COMPUTERS - PC compatibles". 090519 classiccmp.org ...more...

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History of computing hardware

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FNET

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FNET

FNET (Frequency monitoring Network; a.k.a. FNET/GridEye, GridEye) is a wide-area power system frequency measurement system. Using a type of phasor measurement unit (PMU) known as a Frequency Disturbance Recorder (FDR), FNET/GridEye is able to measure the power system frequency, voltage, and angle very accurately. These measurements can then be used to study various power system phenomena, and may play an important role in the development of future smart grid technologies. The FNET/GridEye system is currently operated by the Power Information Technology Laboratory at the University of Tennessee (UTK) in Knoxville, TN and Oak Ridge National Laboratory (ORNL) in Oak Ridge, TN.[1] History A Phasor measurement unit is an important tool that is used to monitor and study electric power systems. The first PMUs were developed at Virginia Tech in the late 1980s. These devices measure the voltage, frequency and phase angle at buses within the power system. By utilizing the Global Positioning System, a PMU can provide a ...more...

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Virginia Tech

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Automatic meter reading

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Automatic meter reading

Older US residential electric meter location, retrofitted with a 1-phase digital smart meter. The meter communicates to its collection point using 900 MHz mesh network topology. Automatic meter reading, or AMR, is the technology of automatically collecting consumption, diagnostic, and status data from water meter or energy metering devices (gas, electric) and transferring that data to a central database for billing, troubleshooting, and analyzing. This technology mainly saves utility providers the expense of periodic trips to each physical location to read a meter. Another advantage is that billing can be based on near real-time consumption rather than on estimates based on past or predicted consumption. This timely information coupled with analysis can help both utility providers and customers better control the use and production of electric energy, gas usage, or water consumption. AMR technologies include handheld, mobile and network technologies based on telephony platforms (wired and wireless), radio ...more...

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Automation

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Uninterruptible power supply

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Uninterruptible power supply

A small free-standing UPS with one IEC 60320 C14 input and three C13 outputs A large datacenter-scale UPS being installed by electricians An uninterruptible power supply or uninterruptible power source (UPS) is an electrical apparatus that provides emergency power to a load when the input power source or mains power fails. A UPS differs from an auxiliary or emergency power system or standby generator in that it will provide near-instantaneous protection from input power interruptions, by supplying energy stored in batteries, supercapacitors, or flywheels. The on-battery run-time of most uninterruptible power sources is relatively short (only a few minutes) but sufficient to start a standby power source or properly shut down the protected equipment. A UPS is typically used to protect hardware such as computers, data centers, telecommunication equipment or other electrical equipment where an unexpected power disruption could cause injuries, fatalities, serious business disruption or data loss. UPS unit ...more...

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Electric power systems components

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High frequency line trap

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High frequency line trap

Electricity pylon with line traps A line trap (high-frequency stopper) is a maintenance-free parallel resonant circuit, mounted inline on high-voltage (HV) AC transmission power lines to prevent the transmission of high frequency (40 kHz to 1000 kHz) carrier signals of power line communication to unwanted destinations. Line traps are cylinder-like structures connected in series with HV transmission lines. A line trap is also called a wave trap.[1] The line trap acts as a barrier or filter to prevent signal losses. The inductive reactance of the line trap presents a high reactance to high-frequency signals but a low reactance to mains frequency. This prevents carrier signals from being dissipated in the substation or in a tap line or branch of the main transmission path and grounds in the case of anything happening outside of the carrier transmission path. The line trap is also used to attenuate the shunting effects of high-voltage lines. Design The trap consists of three major components: the main coil, t ...more...

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Electric power infrastructure

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Power electronics

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Power electronics

An HVDC thyristor valve tower 16.8 m tall in a hall at Baltic Cable AB in Sweden A battery charger is an example of a piece of power electronics A PCs power supply is an example of a piece of power electronics, whether inside or outside of the cabinet Power electronics is the application of solid-state electronics to the control and conversion of electric power. The first high power electronic devices were mercury-arc valves. In modern systems the conversion is performed with semiconductor switching devices such as diodes, thyristors and transistors, pioneered by R. D. Middlebrook and others beginning in the 1950s. In contrast to electronic systems concerned with transmission and processing of signals and data, in power electronics substantial amounts of electrical energy are processed. An AC/DC converter (rectifier) is the most typical power electronics device found in many consumer electronic devices, e.g. television sets, personal computers, battery chargers, etc. The power range is typicall ...more...

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Letter beacon

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Letter beacon

Signal of letter beacon D on 5137.5 kHz Letter beacons are radio transmissions of uncertain origin and unknown purpose, consisting of only a single repeating Morse code letter. They have been classified into a number of groups according to transmission code and frequency, and it is supposed that the source for most of them is Russia. (Some beacons sending Morse code letters are well known directional or non-directional beacons for radio navigation. These are not discussed in this article.) Letter beacons have been referred to as: SLB, or "Single Letter Beacons" SLHFB, or "Single Letter High Frequency Beacons" SLHFM, or "Single Letter High Frequency Markers" Cluster beacons MX — an ENIGMA[NOTES 1] and ENIGMA-2000[NOTES 2] designation. Transmission locations These radio transmissions were discovered in the late 1960s. Their presence became known to the wider amateur radio community in 1978, when beacon “W” started transmitting on 3584 kHz, in the 80 meters band. There is indirect evidence that this ...more...

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Welding power supply

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Welding power supply

A welding power supply is a device that provides an electric current to perform welding.[1][2][3] Welding usually requires high current (over 80 amperes) and it can need above 12,000 amperes in spot welding. Low current can also be used; welding two razor blades together at 5 amps with gas tungsten arc welding is a good example. A welding power supply can be as simple as a car battery and as sophisticated as a high-frequency inverter using IGBT technology, with computer control to assist in the welding process. Classification Welding machines are usually classified as constant current (CC) or constant voltage (CV); a constant current machine varies its output voltage to maintain a steady current while a constant voltage machine will fluctuate its output current to maintain a set voltage. Shielded metal arc welding and gas tungsten arc welding will use a constant current source and gas metal arc welding and flux-cored arc welding typically use constant voltage sources but constant current is also possible wit ...more...

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Power-line communication

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Power-line communication

Power-line communication (PLC) carries data on a conductor that is also used simultaneously for AC electric power transmission or electric power distribution to consumers. It is also known as power-line carrier, power-line digital subscriber line (PDSL), mains communication, power-line telecommunications, or power-line networking (PLN). A wide range of power-line communication technologies are needed for different applications, ranging from home automation to Internet access which is often called broadband over power lines (BPL). Most PLC technologies limit themselves to one type of wires (such as premises wiring within a single building), but some can cross between two levels (for example, both the distribution network and premises wiring). Typically transformers prevent propagating the signal, which requires multiple technologies to form very large networks. Various data rates and frequencies are used in different situations. A number of difficult technical problems are common between wireless and power-l ...more...

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Radio spectrum

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Radio spectrum

The radio spectrum is the part of the electromagnetic spectrum with frequencies from 3 Hz to 3 000 GHz (3 THz). Electromagnetic waves in this frequency range, called radio waves, are extremely widely used in modern technology, particularly in telecommunication. To prevent interference between different users, the generation and transmission of radio waves is strictly regulated by national laws, coordinated by an international body, the International Telecommunication Union (ITU).[1] Different parts of the radio spectrum are allocated by the ITU for different radio transmission technologies and applications; some 40 radiocommunication services are defined in the ITU's Radio Regulations (RR).[2] In some cases, parts of the radio spectrum are sold or licensed to operators of private radio transmission services (for example, cellular telephone operators or broadcast television stations). Ranges of allocated frequencies are often referred to by their provisioned use (for example, cellular spectrum or television s ...more...

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Synchronous motor

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Synchronous motor

A synchronous motor from a Hammond organ Small synchronous motor with integral stepdown gear from a microwave oven A synchronous electric motor is an AC motor in which, at steady state,[1] the rotation of the shaft is synchronized with the frequency of the supply current; the rotation period is exactly equal to an integral number of AC cycles. Synchronous motors contain multiphase AC electromagnets on the stator of the motor that create a magnetic field which rotates in time with the oscillations of the line current. The rotor with permanent magnets or electromagnets turns in step with the stator field at the same rate and as a result, provides the second synchronized rotating magnet field of any AC motor. A synchronous motor is termed doubly fed if it is supplied with independently excited multiphase AC electromagnets on both the rotor and stator. The synchronous motor and induction motor are the most widely used types of AC motor. The difference between the two types is that the synchronous motor ...more...

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Artifact (error)

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Artifact (error)

Diffraction spikes are lens flare artifacts In natural science and signal processing, an artifact is any error in the perception or representation of any information, introduced by the involved equipment or technique(s).[1] Computer science In computer science, digital artifacts are anomalies introduced into digital signals as a result of digital processing. Microscopy In microscopy, artifacts are sometimes introduced during the processing of samples into slide form. See Artifact (microscopy) Econometrics In econometrics, which trades on computing relationships between related variables, an artifact is a spurious finding, such as one based on either a faulty choice of variables or an over extension of the computed relationship. Such an artifact may be called a statistical artifact. For instance, imagine a hypothetical finding that presidential approval rating is approximately equal to twice the percentage of citizens making more than $50,000 annually; if 60% of citizens make more than $50,000 annually, t ...more...

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Error

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Intel Turbo Boost

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Intel Turbo Boost

Intel Turbo Boost is Intel's trade name for a feature that automatically raises certain of its processors' operating frequency, and thus performance, when demanding tasks are running. Turbo-Boost-enabled processors are the Core i5, Core i7 and Core i9 series[1] manufactured since 2008, more particularly, those based on the Nehalem, Sandy Bridge, and later microarchitectures.[2] The frequency is accelerated when the operating system requests the highest performance state of the processor. Processor performance states are defined by the Advanced Configuration and Power Interface (ACPI) specification, an open standard supported by all major operating systems; no additional software or drivers are required to support the technology.[1] The design concept behind Turbo Boost is commonly referred to as "dynamic overclocking".[3] When the workload on the processor calls for faster performance, the processor's clock will try to increase the operating frequency in regular increments as required to meet demand. The inc ...more...

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Kota Super Thermal Power Plant

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Kota Super Thermal Power Plant

Kota Thermal Power Plant is Rajasthan's first major coal-fired power plant. It is located on the west bank of the Chambal River near Kota. Power plant Kota Thermal Power Station has received Meritories productivity awards during 1984, 1987, 1989, 1991 and every year since 1992 onwards.[1] Installed capacity Stage Unit number Installed capacity (MW) Date of commissioning Status Stage I 1 110 January 1983 Running Stage I 2 110 July, 1983 Running Stage II 3 210 September 1988 Running Stage II 4 210 May, 1989 Running Stage III 5 210 March 1994 Running Stage IV 6 195 July, 2003 Running Stage V 7 195 May 2009 Running Features Control room Boiler generator turbine assembly Fully automated control room Fire station Side view Flocculator tank Pumps for water circulation See also Suratgarh Super Thermal Power Plant Giral Lignite Power Plant Chhabra Thermal Power Plant References "Kota Thermal Power Plant". Rajast ...more...

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Kota district

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Radio-frequency identification

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Radio-frequency identification

Small RFID chips, here compared to a grain of rice, are incorporated in consumer products, and implanted in pets, for identification purposes Radio-frequency identification (RFID) uses electromagnetic fields to automatically identify and track tags attached to objects. The tags contain electronically-stored information. Passive tags collect energy from a nearby RFID reader's interrogating radio waves. Active tags have a local power source (such as a battery) and may operate hundreds of meters from the RFID reader. Unlike a barcode, the tag need not be within the line of sight of the reader, so it may be embedded in the tracked object. RFID is one method for Automatic Identification and Data Capture (AIDC).[1] RFID tags are used in many industries, for example, an RFID tag attached to an automobile during production can be used to track its progress through the assembly line; RFID-tagged pharmaceuticals can be tracked through warehouses; and implanting RFID microchips in livestock and pets allows for positi ...more...

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Higashi-Shimizu Frequency Converter

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Higashi-Shimizu Frequency Converter

Location of Higashi-Shimizu Frequency Converter and Japan's two utility frequencies Schematic of Higashi-Shimizu Frequency Converter Higashi-Shimizu Frequency Converter is the third facility in Japan for interconnecting the power grid of Eastern Japan, which is operated with 50 hertz to that of Western Japan, which is operated with 60 hertz. The Higashi-Shimizu Frequency Converter Station, which is operated by Chubu Electric Power Co and situated northeast of Shimizu at 677-3 Tanakake, Hirose-aza, Shimizu-ku, Shizuoka is fed over a 275 kV power line and over a 154 kV power line. Its inverters operate with a DC voltage of 125 kV and have a maximum transmission rate of 300 MW. Other stations are at Shin Shinano, Sakuma Dam, and Minami-Fukumitsu. See also Energy in Japan External links http://www.chuden.co.jp/english/corporate/press2005/0323_1.html ...more...

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Digital clock

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Digital clock

Basic digital alarm clock without a radio. The mark in the top-left of the display indicates that the time is 4:00pm, not 4:00am. A 1969 radio alarm clock (Sony Digimatic 8FC-59W) with an early mechanical-digital display A digital clock is a type of clock that displays the time digitally (i.e. in numerals or other symbols), as opposed to an analog clock, where the time is indicated by the positions of rotating hands. Digital clocks are often associated with electronic drives, but the "digital" description refers only to the display, not to the drive mechanism. (Both analog and digital clocks can be driven either mechanically or electronically, but "clockwork" mechanisms with digital displays are rare.) The biggest digital clock is the Lichtzelt Pegel ("Light Time Level") on the television tower Rheinturm Düsseldorf, Germany. History The first digital pocket watch was the invention of Austrian engineer Josef Pallweber who created his "jump-hour" mechanism in 1883. Instead of a conventional dial, the ...more...

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Telangana Power Generation Corporation

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Telangana Power Generation Corporation

Telangana Power Generation Corporation Limited is a power generating organization of Telangana.[2] It has ceased to do power trading and has retained with powers of controlling system operations of Power Generation after formation of Telangana state.[3] Telangana Power Generation Corporation Limited has been incorporated under companies Act, 2013, on 19 May 2014 and commenced its operations from 2 June 2014.[4] History The erstwhile Andhra Pradesh State Electricity Board which came into existence in 1959 was responsible for Generation, Transmission and Distribution of Electricity.Under Electricity Sector Reforms agenda,Government of Andhra Pradesh promulgated Andhra Pradesh Electricity Reforms Act, 1998. The erstwhile APSEB was unbundled into one Generating Company (APGENCO), One Transmission Company (APTRANSCO) and Four Distribution Companies (APDISCOMs) as part of the reform process. Later, on 2 June 2014, when the state was bifurcated, APGENCO distributed all the assets, liabilities and power stations t ...more...

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Companies started in 2014

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PAL

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PAL

Television encoding systems by nation; countries now using (and once using) the PAL system are shown in blue. Phase Alternating Line (PAL) is a color encoding system for analogue television used in broadcast television systems in most countries broadcasting at 625-line / 50 field (25 frame) per second (576i). Other common colour encoding systems are NTSC and SECAM. All the countries using PAL are currently in process of conversion or have already converted standards to DVB, ISDB or DTMB. This page primarily discusses the PAL colour encoding system. The articles on broadcast television systems and analogue television further describe frame rates, image resolution and audio modulation. History In the 1950s, the Western European countries started planning to introduce colour television, and were faced with the problem that the NTSC standard demonstrated several weaknesses, including colour tone shifting under poor transmission conditions, which became a major issue considering Europe's geographical and weat ...more...

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Suratgarh Super Thermal Power Plant

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Suratgarh Super Thermal Power Plant

Suratgarh Super Thermal Power Station is Rajasthan's first super thermal power station. It is located 27 km away from Suratgarh town in Ganganagar district. The power plant is operated by Rajasthan Rajya Vidyut Utpadan Nigam Ltd (RVUNL). The power plant has 6 units that can produce 250 megawatts each. Awards The plant received a gold shield on August 8, 2004 from Hon'ble President for consistently outstanding performance during the years 2000 to 2004. It also received a bronze shield from Hon' Prime Minisr for outstanding performance during the years 2005 and 2006.[1] Installed capacity Following is the unit wise capacity of the plant.[2] Stage Unit Number Installed Capacity (MW) Date of Commissioning Status Stage I 1 250 May, 1998 Running Stage I 2 250 March, 2000 Running Stage II 3 250 October, 2001 Running Stage II 4 250 March, 2002 Running Stage III 5 250 June, 2003 Running Stage IV 6 250 March, 2009 Running Stage V 7 660 2016 Work in progress(Drainable Hydro Test has been successfully ...more...

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Sri Ganganagar district

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Wide-area damping control

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Wide-area damping control

Wide-area damping control (WADC) is a class of automatic control systems used to provide stability augmentation to modern electrical power systems known as smart grids. Actuation for the controller is provided via modulation of capable active or reactive power devices throughout the grid. Such actuators are most commonly previously-existing power system devices, such as high-voltage DC (HVDC) transmission lines and static VAR compensators (SVCs) which serve primary purposes not directly related to the WADC application. However, damping may be achieved with the utilization of other devices installed with the express purpose of stability augmentation, including energy storage technologies. Wide-area instability of a large electrical grid unequipped with a WADC is the result of the loss of generator rotor synchronicity and is typically envisioned as a generator (or group of generators) oscillating with an undamped exponential trajectory as the result of insufficient damping torque. Rotor Instability Phenomena L ...more...

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Load management

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Load management

Load management, also known as demand side management (DSM), is the process of balancing the supply of electricity on the network with the electrical load by adjusting or controlling the load rather than the power station output. This can be achieved by direct intervention of the utility in real time, by the use of frequency sensitive relays triggering the circuit breakers (ripple control), by time clocks, or by using special tariffs to influence consumer behavior. Load management allows utilities to reduce demand for electricity during peak usage times (peak shaving), which can, in turn, reduce costs by eliminating the need for peaking power plants. In addition, some peaking power plants can take more than an hour to bring on-line which makes load management even more critical should a plant go off-line unexpectedly for example. Load management can also help reduce harmful emissions, since peaking plants or backup generators are often dirtier and less efficient than base load power plants. New load-managemen ...more...

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