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Utility frequency

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.


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,

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.

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]

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 (Kyoto 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.


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.

Time 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 and 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.
  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 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".
  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
  22. Time Error Correction.
  23. "National Grid: Real Time Frequency Data – Last 60 Minutes".
  24. "Dynamic Demand".
  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".
  29. "First Solar Proves That PV Plants Can Rival Frequency Response Services From Natural Gas Peakers". 19 January 2017. Retrieved 20 January 2017.
  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


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 and no apparent desire for complete worldwide standardization ...more...



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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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 frequency, f ...more...

High frequency


HF's position in the electromagnetic spectrum. High frequency (HF) is the ITU designation 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, weat ...more...

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. 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 isolati ...more...



GPU-Z is a lightweight utility designed to provide information about video cards and GPUs . 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 GPU core clock 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". Retrieved 2017-06-05. External links Official website GPU-Z is a lightweight utility designed to ...more...

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. 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; 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 and software. VFDs are made in a number of differen ...more...

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 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. But in the case of goalkeepers playing as outfield players, it is extremely rare. Some may be free kick and penalty specialists (Rogério Ceni, José Luis Chilavert and Jorge Campos), but they do not hold a role in the ...more...

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. 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. They are usually quite large to take advantage of economies of scale. The electric power which is generated is stepped up to a higher voltage at which it connects to the electric power transmission network. 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 th ...more...

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) . FHSS is a wireless technology that spreads its signal over rapidly changing frequencies. Each available frequency band is divided into sub-frequencies. Signals rapidly change ("hop") among these in a pre-determined 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-spectr ...more...

Continental U.S. power transmission grid


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 and Canada, 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; however, 120 V is the nominal voltage. History In the United States in the 1920s, utilities formed joint-ope ...more...

Solar inverter


A solar inverter, or converter or PV inverter, 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 Solar inverters may be classified into three broad types: Stand-alone inverters, used in isolated systems where the inverter draws its DC energy from batteries charged by photovoltaic arrays. Many stand-alone inverters also incorporate integral battery chargers to replenish the battery from an AC source, when available. Normally these do not interface ...more...

Transfer switch


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 transfer switch may be Open Transition (OT) (th ...more...

Automatic meter reading


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 frequency (RF), or powerline transmission. Technologies Touch technology With touch-based AMR, a meter reader carries a handheld computer or data collection device with a wand ...more...

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 ea ...more...

Grid-connected photovoltaic power system


A grid-connected, residential solar rooftop system near Boston, USA A grid-connected photovoltaic power system, or grid-connected PV power system is an electricity generating solar PV power system that is connected to the utility grid. A grid-connected PV system consists of solar panels, one or several inverters, a power conditioning unit and grid connection equipment. They range from small residential and commercial rooftop systems to large utility-scale solar power stations. Unlike stand-alone power systems, a grid-connected system rarely includes an integrated battery solution, as they are still very expensive. When conditions are right, the grid-connected PV system supplies the excess power, beyond consumption by the connected load, to the utility grid. Operation Photovoltaic power station at Nellis Air Force Base, United States Residential, grid-connected rooftop systems which have a capacity more than 10 kilowatts can meet the load of most consumers. They can feed excess power to the grid wher ...more...

Welding power supply


A welding power supply is a device that provides an electric current to perform welding. 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 with a vol ...more...



Look up hq in Wiktionary, the free dictionary. HQ often refers to headquarters. HQ may also refer to: Arts and entertainment HQ (album), a 1975 album by Roy Harper Chase H.Q., an arcade racing game HeroQuest (role-playing game) HQ (app), a live trivia game app Businesses and utilities Hagströmer & Qviberg, a Swedish investment bank Harmony Airways (IATA airline designator) Home Quarters Warehouse, a defunct retail chain Hydro-Québec, an electrical power utility of Québec, Canada Thomas Cook Airlines Belgium (IATA airline code) Other uses Geely HQ (Haoqing), a car model HAVE QUICK, a frequency-hopping system used to protect military UHF radio traffic The FIPS PUB 10-4 territory code for Howland Island Twickenham Stadium, a rugby union stadium in London, England often called "HQ" Holden HQ, a range of car models Abbreviated form of high quality Look up hq in Wiktionary, the free dictionary. HQ often refers to headquarters. HQ may also refer to: Arts and entertainment HQ (album) ...more...

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). 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). 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 spectru ...more...

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 manufactured since 2008, more particularly, those based on the Nehalem, Sandy Bridge, and later microarchitectures. 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. The design concept behind Turbo Boost is commonly referred to as "dynamic overclocking". 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 increased clock ...more...

Frequentist probability


John Venn Frequentist probability or frequentism is an interpretation of probability; it defines an event's probability as the limit of its relative frequency in a large number of trials. This interpretation supports the statistical needs of experimental scientists and pollsters; probabilities can be found (in principle) by a repeatable objective process (and are thus ideally devoid of opinion). It does not support all needs; gamblers typically require estimates of the odds without experiments. The development of the frequentist account was motivated by the problems and paradoxes of the previously dominant viewpoint, the classical interpretation. In the classical interpretation, probability was defined in terms of the principle of indifference, based on the natural symmetry of a problem, so, e.g. the probabilities of dice games arise from the natural symmetric 6-sidedness of the cube. This classical interpretation stumbled at any statistical problem that has no natural symmetry for reasoning. Definition ...more...

Letter beacon


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 and ENIGMA-2000 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 particular transmitter was located in Cuba. In 1982 there were als ...more...

Mains electricity


Mains electricity 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 travelers, since portable appliances designed for one voltage and frequency combination may not operate with, or may even be destroyed by another. The use of different and incompatible plugs and sockets in different regions and countries provides some protection from accidental use ...more...

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 mai ...more...

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...

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. 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, th ...more...

Cardinal utility


In economics, a cardinal utility function or scale is a utility index that preserves preference orderings uniquely up to positive affine transformations. 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 for fixed constants a and b. Thus the utility functions themselves are related by The two indices differ only with respect to scale and origin. Thus if one is concave, so is the other, in which case there is often said to be diminishing marginal utility. Thus the use of cardinal utility imposes the assumption that levels of absolute satisfaction exist, so that the magnitudes of increments to satisfaction can be compared across different situations. The idea of cardinal utility is considered o ...more...



RG-6 coaxial cable for television signals RG-6 coaxial cable RG-6/U is a common type of coaxial cable used in a wide variety of residential and commercial applications. An RG-6/U coaxial cable has a characteristic impedance of 75 ohms. The term, RG-6, is generic and is applied to a wide variety of cable designs, which differ from one another in shielding characteristics, center conductor composition, dielectric type and jacket type. RG was originally a unit indicator for bulk radio frequency (RF) cable in the U.S. military's Joint Electronics Type Designation System. The suffix /U means for general utility use. The number was assigned sequentially. The RG unit indicator is no longer part of the JETDS system (MIL-STD-196E) and cable sold today under the RG-6 label is unlikely to meet military specifications. In practice, the term RG-6 is generally used to refer to coaxial cables with an 18 AWG (1.024 mm) center conductor and 75 ohm characteristic impedance. Applications The most commonly recognized v ...more...

Utility Radio


The Utility Radio or Wartime Civilian Receiver was a valve domestic radio receiver, manufactured in Great Britain during World War II starting in July 1944. It was designed by G.D Reynolds of Murphy Radio. Both AC and battery-operated versions were made. History When war broke out in 1939, British radio manufacturers devoted their resources to producing a range of military radio equipment required for the armed forces. This resulted in a shortage of consumer radio sets and spare parts, particularly valves, as all production was for the services. The war also prompted a shortage of radio repairmen, as virtually all of them were needed in the services to maintain vital radio and radar equipment. This meant it was very difficult for the average citizen to get a radio repaired, and with very few new sets available, there was a desperate need to overcome the problem. The Government solved this by arranging for over 40 radio manufacturers to produce sets to a standard design with as few components as possible c ...more...

Cable television


The bottom product is a set-top box, an electronic device which cable subscribers use to connect the cable signal to their television set. Cable television is a system of delivering television programming to paying subscribers via radio frequency (RF) signals transmitted through coaxial cables, or in more recent systems, light pulses through fiber-optic cables. This contrasts with broadcast television, in which the television signal is transmitted over the air by radio waves and received by a television antenna attached to the television; or satellite television, in which the television signal is transmitted by a communications satellite orbiting the Earth and received by a satellite dish on the roof. FM radio programming, high-speed Internet, telephone services, and similar non-television services may also be provided through these cables. Analog television was standard in the 20th century, but since the 2000s, cable systems have been upgraded to digital cable operation. A "cable channel" (sometimes known ...more...

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. 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. History The late 1870s ...more...

Power inverter


An inverter on a free-standing solar plant Overview of solar-plant inverters A power inverter, or inverter, is an electronic device or circuitry that changes direct current (DC) to alternating current (AC). The input voltage, output voltage and frequency, and overall power handling depend on the design of the specific device or circuitry. The inverter does not produce any power; the power is provided by the DC source. A power inverter can be entirely electronic or may be a combination of mechanical effects (such as a rotary apparatus) and electronic circuitry. Static inverters do not use moving parts in the conversion process. Input and output Input voltage A typical power inverter device or circuit requires a relatively stable DC power source capable of supplying enough current for the intended power demands of the system. The input voltage depends on the design and purpose of the inverter. Examples include: 12 V DC, for smaller consumer and commercial inverters that typically run from a recha ...more...

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Folder: car inverter


Power inverters can be very big and hefty—especially if they have built-in battery packs so they can work in a standalone way. They also generate lots of heat, which is why they have large heat sinks (metal fins) and often cooling fans as well. As you can see from our top photo, typical ones are about as big as a car battery or car battery charger; larger units look like a bit like a bank of car batteries in a vertical stack. The smallest inverters are more portable boxes the size of a car radio that you can plug into your cigarette lighter socket to produce AC for charging laptop computers or cellphones. Car Inverter Company is a leader among inverter manufacturer. Our main focus is creating the highest quality products. Car Inverter Company is an america inverter company located in Los Angeles. Our company concentrates on inverter design and inverter manufacture. The main products are car inverter, home inverter, pure sine wave inverter, 12v to 220v inverter and so on. The main function of an inverter is to convert direct current (DC) into alternating current (AC), and to change the voltage level into a stable 120 or 240 VAC that can be used by household appliances or "sold back" to the utility grid. The word "inverter" was originally used because the output wave form produced by its circuits alternates between a positive and a negative voltage. This device "inverts" the polarity of the power source (typically, a battery or PV array), causing the current to flow in alternating directions through the load. Hence the term "alternating current". A car inverter is an electrical device for converting 12-volt DC battery power into 120 volt AC power. Inverters are available in sizes ranging from as low as 30 watts up to 4,000 watts or more. For pratical purposes, an inverter size of 2,000-3,000 watts will be needed (or will already be installed) in an RV. There are two basic kinds of inverters:pure sine wave inverter and modified sine wave inverter. pure sine wave is what comes out of the wall. Modified sine wave is basically a square wave with the corners smoothed a little. Most stores only carry modified sine inverters because they are a lot cheaper. Operation of an inverter is, for the most part, automatic, although most require some settings to be programmed. When shore &/or generator power is lost, the inverter senses this and provides its own power to maintain an uninterupted power source. When shore power is restored or the generator started, the inverter will again sense this and, usually after a short delay, will automatically switch shore or generator power to the RV. Battery charging can also occur automatically, although it's usually possible to override this manually. There are two basic types of inverter available, known as modified sine-wave inverter and pure sine wave inverter, the former being the most common and least costly. Some appliances have been reported to not run on a modified sine-wave inverter, although the author has not experienced this with various inverters I've installed in RVs and boats. Our power inverter line has input voltages ranging from 12 volt dc power inverters, 24 volt dc power inverters and 48 volt dc power inverters. You will find a complete line of industrial grade power inverters, available in 12 volt, 24 volt and 48 volts. Our industrial power inverters are built tough and ready for use in commercial applications. We also offers 220 50hz export power inverters. The Export power inverters that we offer are modified sine 220 50hz power inverters, which are designed to be used in Africa and Europe. These 220 50hz power inverters are available in both 12 volt and 48 volt. Visit to learn more.

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 movement, used in the Seiko ...more...

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. 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. 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. In 2009 Beacon received a loan guarantee from the United States Department of Energy (DOE) for $43 million to build a 20-megaw ...more...

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 t ...more...



RMClock, short for RightMark CPU Clock Utility (formerly known as AMD64CLK), is software developed by, distributed under the brand RightMark Gathering. A free version is available as is a licensed "pro" version. RightMark CPU Clock Utility (RMClock) is a small GUI application designed for real-time CPU frequency, throttling, load level monitoring, and on-the-fly adjustment of the CPU performance level on supported CPU models via the processor's power management model-specific registers (MSRs). In automatic management mode it continuously monitors the CPU usage level and dynamically adjusts the CPU frequency, throttle and/or voltage level as needed, realizing the "Performance on Demand" concept. RMClock is confirmed to work on Windows XP, Windows Vista, Windows 7. Currently RMClock only supports the 64-bit versions of Vista and Windows 7 in a limited way. The last version was released in 2008 and no further development has been undertaken. Common usage Underclocking and/or Reducing voltage to sa ...more...



A clothespin (US English), or clothes peg (UK English) is a fastener used to hang up clothes for drying, usually on a clothes line. Clothespins often come in many different designs. Design A one-piece wooden clothespin Plastic clothespin Not to be confused with the one-piece wooden clothes-peg for hanging up coats that was invented by the Shaker community in the 1700s. During the 1700s laundry was hung on bushes, limbs or lines to dry but no clothespins can be found in any painting or prints of the era. The clothespin for hanging up wet laundry only appears in the early 19th century patented by Jérémie Victor Opdebec. This design does not use springs, but is fashioned in one piece, with the two prongs part of the peg chassis with only a small distance between them—this form of peg creates the gripping action due to the two prongs being wedged apart and thus squeezing together in that the prongs want to return to their initial, resting state. This form of peg is often fashioned from plastic, or or ...more...

Rooftop photovoltaic power station


A rooftop photovoltaic power station, or rooftop PV system, is a photovoltaic system that has its electricity-generating solar panels mounted on the rooftop of a residential or commercial building or structure. The various components of such a system include photovoltaic modules, mounting systems, cables, solar inverters and other electrical accessories. Rooftop mounted systems are small compared to ground-mounted photovoltaic power stations with capacities in the megawatt range. Rooftop PV systems on residential buildings typically feature a capacity of about 5 to 20 kilowatts (kW), while those mounted on commercial buildings often reach 100 kilowatts or more. Installation Rooftop PV systems at Googleplex, California The urban environment provides a large amount of empty rooftop spaces and can inherently avoid the potential land use and environmental concerns. Estimating rooftop solar insolation is a multi-faceted process, as insolation values in rooftops are impacted by the following: Time of the ...more...

Radio-frequency identification


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). 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 positive identification of animals. Since RFID tags can be attached to cash, clothing, and possessions, or implanted in animals and people, the possibil ...more...



A section of RG-59 cable with its end stripped. Outer plastic sheath Copper braid shield Inner dielectric insulator Copper-plated core (sometimes solid core) RG-59/U is a specific type of coaxial cable , often used for low-power video and RF signal connections. The cable has a characteristic impedance of 75 ohms , and a capacitance of around 20pF/ft (60pF/m). The 75 ohm impedance matches a dipole antenna in free space. RG (for radio guide) was originally a unit indicator for bulk radio frequency (RF) cable in the U.S. military's Joint Electronics Type Designation System . The suffix /U means for general utility use. The number 59 was assigned sequentially. The RG unit indicator is no longer part of the JETDS system (MIL-STD-196E) and cable sold today under the RG-59 label does not necessarily meet military specifications. RG-59 is often used at baseband video frequencies, such as composite video . It may also be used for broadcast frequencies, but its high-frequency losses are too high to allow its use over ...more...

Cherry Ripe (numbers station)


Cherry Ripe is the nickname of a discontinued shortwave numbers station that used several bars from the English folk song "Cherry Ripe" as an interval signal. The station was believed to be operated by the British Secret Intelligence Service and to have emanated from Australia. It was thought to have previously broadcast from Guam. It consisted of an electronically synthesised English-accented female voice reading groups of five numbers, e.g. "3-5-7-6-1". It is likely that the station was used to communicate messages to undercover agents operating in other countries, to be decoded using a one-time pad. Cherry Ripe had a more famous and much more active Middle-Eastern cousin, the Lincolnshire Poacher, which also used several bars from the English folk song of the same name as its interval signal. The Lincolnshire Poacher had long been suspected as being operated by Britain and had been detected as emanating from RAF Akrotiri on Cyprus. Apart from the interval signal, the format and voice of the two stations w ...more...

Gutmann method


The Gutmann method is an algorithm for securely erasing the contents of computer hard disk drives, such as files. Devised by Peter Gutmann and Colin Plumb and presented in the paper Secure Deletion of Data from Magnetic and Solid-State Memory in July 1996, it involved writing a series of 35 patterns over the region to be erased. The selection of patterns assumes that the user does not know the encoding mechanism used by the drive, so it includes patterns designed specifically for three types of drives. A user who knows which type of encoding the drive uses can choose only those patterns intended for their drive. A drive with a different encoding mechanism would need different patterns. Most of the patterns in the Gutmann method were designed for older MFM/RLL encoded disks. Gutmann himself has noted that more modern drives no longer use these older encoding techniques, making parts of the method irrelevant. He said "In the time since this paper was published, some people have treated the 35-pass overwrite t ...more...

Ground-penetrating radar


Ground-penetrating radar (GPR) is a geophysical method that uses radar pulses to image the subsurface. This nondestructive method uses electromagnetic radiation in the microwave band (UHF/VHF frequencies) of the radio spectrum, and detects the reflected signals from subsurface structures. GPR can have applications in a variety of media, including rock, soil, ice, fresh water, pavements and structures. In the right conditions, practitioners can use GPR to detect subsurface objects, changes in material properties, and voids and cracks. GPR uses high-frequency (usually polarized) radio waves, usually in the range 10 MHz to 2.6 GHz. A GPR transmitter emits electromagnetic energy into the ground. When the energy encounters a buried object or a boundary between materials having different permittivities, it may be reflected or refracted or scattered back to the surface. A receiving antenna can then record the variations in the return signal. The principles involved are similar to seismology, except GPR methods impl ...more...

Mains hum


Mains hum , electric hum , or power line hum is a sound associated with alternating current at the frequency of the mains electricity . The fundamental frequency of this sound is usually 50  Hz or 60 Hz, depending on the local power-line frequency . The sound often has heavy harmonic content above 50–60 Hz. Because of the presence of mains current in mains-powered audio equipment as well as ubiquitous AC electromagnetic fields from nearby appliances and wiring, 50/60 Hz electrical noise can get into audio systems, and is heard as mains hum from their speakers. Mains hum may also be heard coming from powerful electric power grid equipment such as utility transformers , caused by mechanical vibrations induced by the powerful AC current in them. Causes of electric hum Electric hum around transformers is caused by stray magnetic fields causing the enclosure and accessories to vibrate. Magnetostriction is a second source of vibration, in which the core iron changes shape minutely when exposed to magnetic fields. T ...more...

Phase converter


A phase converter is a device that converts electric power provided as single phase to multiple phase or vice versa. The majority of phase converters are used to produce three-phase electric power from a single-phase source, thus allowing the operation of three-phase equipment at a site that only has single-phase electrical service. Phase converters are used where three-phase service is not available from the utility, or is too costly to install due to a remote location. A utility will generally charge a higher fee for a three-phase service because of the extra equipment for transformers and metering and the extra transmission wire. Conversion systems Three-phase induction motors may operate adequately on an unbalanced supply if not heavily loaded. This allows various imperfect techniques to be used. A single-phase motor can drive a three-phase generator, which will produce a high-quality three-phase source but with high cost for apparatus. Several methods exist to run three-phase motors from a single-phas ...more...

Flicker fusion threshold


The flicker fusion threshold (or flicker fusion rate) is a concept in the psychophysics of vision. It is defined as the frequency at which an intermittent light stimulus appears to be completely steady to the average human observer. Flicker fusion threshold is related to persistence of vision. Although flicker can be detected for many waveforms representing time-variant fluctuations of intensity, it is conventionally, and most easily, studied in terms of sinusoidal modulation of intensity. There are seven parameters that determine the ability to detect the flicker: the frequency of the modulation; the amplitude or depth of the modulation (i.e., what is the maximum percent decrease in the illumination intensity from its peak value); the average (or maximum—these can be inter-converted if modulation depth is known) illumination intensity; the wavelength (or wavelength range) of the illumination (this parameter and the illumination intensity can be combined into a single parameter for humans or other animals ...more...

Free-floating barrel


CheyTac .408 sniper rifle. A free-floating barrel is a specific design technology used in highly accurate rifles, particularly match grade rifles, to increase the accuracy of the weapon. With conventional rifles, the barrel rests in contact with the fore-end of the stock. If the stock is manufactured from wood, environmental conditions or operational use may warp the wood, which may cause the barrel to shift its alignment slightly over time as well, altering the projectile's external ballistics and point of impact. Contact between the barrel and the stock also interferes with the natural frequency of the barrel, which can have a detrimental effect on accuracy especially when the barrel gets hot with repeated firing. The interference of the stock with the barrel's oscillation harmonics as the bullet passes down the bore can cause the barrel to vibrate inconsistently from shot to shot, depending on the external forces acting upon the stock at the time of the shot. Micro-vibrations acting during the bullet's ...more...

Traction substation


Karlsruhe traction current converter plant Woburn rail traction substation in Lower Hutt, New Zealand, supplying 1500 V DC to the electrified Hutt Valley Line. A traction substation or traction current converter plant is an electrical substation that converts electric power from the form provided by the electrical power industry for public utility service to an appropriate voltage, current type and frequency to supply railways, trams (streetcars) or trolleybuses with traction current. Conversions These systems can be used to convert three-phase 50Hz or 60Hz alternating current (AC) for the supply of AC railway electrification systems at a lower frequency and single phase, as used by many older systems, or to rectify AC into direct current (DC) for those systems (primarily public transit systems) using DC for traction power. Equipment Rotating Originally, the conversion equipment usually consisted of one or more motor-generator sets containing three-phase synchronous AC motors and single-phase AC ...more...

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 typic ...more...

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