Monday, December 21, 2009
50 HZs
You need alternating current to operate a transformer. (It does not work with DC). Transformers are required to step up and down the voltage which is required to transport electric energy in an economic way. frequency's of 40 to 400 Hz work fairly well for transformers, and the choice with in this range must have been fairly arbitrairly. But one can imagine that the number 60 is inspired minutes of a clock, wher as the number 50 is inspired by the decimal number counting (a half of 100). By the way 60 Hz is slightly more efficient. A US transformer often has a hard life in Europe. For weight saving the frequency of installations in airplanes are historically 400Hz. Transformers can be much smaller this way.
50Hzs
Utility frequency
From Wikipedia, the free encyclopedia
The waveform of 230 volt, 50 Hz compared with 110 V, 60 Hz.
The line frequency (American English) or mains frequency (British English) is the frequency at which alternating current (AC) is transmitted from a power plant to the end user. In most parts of the world this is 50 Hz, although in the Americas it is typically 60 Hz. Precise details are shown in the list of countries with mains power plugs, voltages and frequencies.
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 100-120 V. Both frequencies co-exist today (some countries such as Japan use both) with no technical reason to prefer one over the other 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.
Contents [hide]
1 Operating factors
1.1 Lighting
1.2 Rotating machines
1.3 Transmission and transformers
1.4 System interconnection
2 History
2.1 25 Hz origins
2.2 40 Hz origins
2.3 Standardization
3 Railways
4 400 Hz
5 Stability
5.1 Long-term stability and clock synchronization
5.2 Frequency and load
6 Audible noise and interference
7 See also
8 Further reading
9 References
[edit]Operating factors
Several factors influence the choice of frequency in an AC system.[1] 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 the 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.
[edit]Lighting
The first applications of commercial electric power were incandescent lighting and commutator-type electric motors. Both devices operate well on DC, but DC cannot be easily transmitted long distances at utilization voltage and also cannot be easily changed in 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.
[edit]Rotating machines
Commutator-type motors do not operate well on high-frequency AC since the rapid changes of current are opposed by the inductance of the motor field; even today, although commutator-type universal motors are common in 50 Hz and 60 Hz household appliances, 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 induction 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. Direct-driven generators off steam turbines after about 1906 favored higher frequencies. The steadier rotation speed of high-speed machines allowed for satisfactory operation of commutators in rotary converters.[2]
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.
[edit]Transmission and transformers
With AC, transformers can be used to step down high transmission voltages to lower utilization voltage. 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.
[edit]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.
[edit]History
Utility frequencies currently in use.
Many different power frequencies were used in the 19th century.
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.[3] 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 2000 RPM, giving a frequency of 133 cycles per second.
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, allegedly because 60 was not a preferred number. AEG's choice of 50 Hz is thought by some to relate to a more "metric-friendly" number than 60. 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.[4]
Westinghouse Electric decided to standardize on a lower 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] Frequencies much below 50 Hz gave noticeable flicker of arc or incandescent lighting. The operation of Tesla's induction motor required a lower frequency than the 133 Hz common for lighting systems in 1890. 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.
[edit]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.[6] Because the Niagara project was so influential on electric power systems design, 25 Hz prevailed as the North American standard for low-frequency AC.
[edit]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.[7] The oldest continuously-operating commercial hydroelectric power plant in the United States, at Mechanicville, New York, 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.
[edit]Standardization
In the early days of electrification, so many frequencies were used that no one value prevailed (London in 1918 had 10 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 interconection 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, 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.
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 USA, and for railway electrification. In the 1950s, many 25 Hz systems, from the generators right through to household appliances, were converted and standardized. Some 25 Hz generators still exist at the Beck 1 and Rankine generating stations 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 electrical generator power station exist in New Orleans for floodwater pumps [1]. Some of the metre gauge railway lines in Switzerland operate at 16⅔ Hz, which can obtained from the local 50 Hz 3 phase power grid through frequency converters.
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.[8] Converters for production of DC from alternating current were larger and 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 consume 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, the Southern California Edison company had standardized on 50 Hz [9]. 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.[10]
In Mexico, areas operating on 50 Hz grid were converted during the 1970s, uniting the country under 60 Hz.[11]
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.
Utility Frequencies in Use in 1897 in North America [12]
Cycles 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 "increasing 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
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 [13] 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)
Cycles 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.
[edit]Railways
Main article: List of current systems for electric rail traction
Other power frequencies are used. Germany, Austria, Switzerland, Sweden and Norway use traction power networks for railways, distributing single-phase AC at 16.7 Hz[14]. A frequency of 25 Hz is used for the Austrian railway Mariazeller Bahn and some railway systems in New York and Pennsylvania (Amtrak) in the USA. Other 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 generating stations. In the 19th Century frequencies as low as 8 Hz were contemplated for operation of electric railways with commutator motors [1] Some outlets in trains carry the correct voltage, but using the original train network frequency like 16⅔ Hz.
[edit]400 Hz
Frequencies as high as 400 Hz are used in submarines, aerospace, spacecraft and server rooms for computer power and hand-held machine tools. Such high frequencies cannot be economically transmitted long distances, so 400 Hz power systems are usually confined to a building or vehicle. 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. This is an application suitable for switched-mode power supplies.
[edit]Stability
[edit]Long-term stability and clock synchronization
Regulation of power system frequency for timekeeping accuracy was not commonplace until after 1926 and the invention of the electric clock driven by a synchronous motor. Network operators will 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.[15] In the continental European UCTE grid, the deviation between network phase time and UTC is calculated at 08:00 each day in a control center in Switzerland, and the target frequency is then adjusted by up to ±0.02% from 50 Hz as needed, to ensure a long-term frequency average of exactly 3600×24×50 cycles per day is maintained.[16] 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.[17][18] A dynamicdemand.co.uk/grid - Real-time frequency meter for power generation in the United Kingdom is available online. Smaller power systems may not maintain frequency with the same degree of accuracy.
[edit]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 so 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. AGC (automatic generation control) is used to maintain scheduled frequency and interchange power flows. Control systems in power plants 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.
Frequency protection 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.[19][20]
[edit]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. It is usually produced by motor and transformer core laminations vibrating in time with the magnetic field. This hum is often evident in poorly made audio amplifiers as well, where the power supply is inadequately filtered.
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 helps prevent power line hum and magnetic interference from causing visible beat frequencies in the displayed picture of analog receivers, but is of diminishing importance in modern digital display systems.
[edit]See also
Mains electricity
Mains power systems
List of countries with mains power plugs, voltages and frequencies
Power connector
From Wikipedia, the free encyclopedia
The waveform of 230 volt, 50 Hz compared with 110 V, 60 Hz.
The line frequency (American English) or mains frequency (British English) is the frequency at which alternating current (AC) is transmitted from a power plant to the end user. In most parts of the world this is 50 Hz, although in the Americas it is typically 60 Hz. Precise details are shown in the list of countries with mains power plugs, voltages and frequencies.
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 100-120 V. Both frequencies co-exist today (some countries such as Japan use both) with no technical reason to prefer one over the other 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.
Contents [hide]
1 Operating factors
1.1 Lighting
1.2 Rotating machines
1.3 Transmission and transformers
1.4 System interconnection
2 History
2.1 25 Hz origins
2.2 40 Hz origins
2.3 Standardization
3 Railways
4 400 Hz
5 Stability
5.1 Long-term stability and clock synchronization
5.2 Frequency and load
6 Audible noise and interference
7 See also
8 Further reading
9 References
[edit]Operating factors
Several factors influence the choice of frequency in an AC system.[1] 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 the 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.
[edit]Lighting
The first applications of commercial electric power were incandescent lighting and commutator-type electric motors. Both devices operate well on DC, but DC cannot be easily transmitted long distances at utilization voltage and also cannot be easily changed in 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.
[edit]Rotating machines
Commutator-type motors do not operate well on high-frequency AC since the rapid changes of current are opposed by the inductance of the motor field; even today, although commutator-type universal motors are common in 50 Hz and 60 Hz household appliances, 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 induction 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. Direct-driven generators off steam turbines after about 1906 favored higher frequencies. The steadier rotation speed of high-speed machines allowed for satisfactory operation of commutators in rotary converters.[2]
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.
[edit]Transmission and transformers
With AC, transformers can be used to step down high transmission voltages to lower utilization voltage. 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.
[edit]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.
[edit]History
Utility frequencies currently in use.
Many different power frequencies were used in the 19th century.
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.[3] 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 2000 RPM, giving a frequency of 133 cycles per second.
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, allegedly because 60 was not a preferred number. AEG's choice of 50 Hz is thought by some to relate to a more "metric-friendly" number than 60. 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.[4]
Westinghouse Electric decided to standardize on a lower 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] Frequencies much below 50 Hz gave noticeable flicker of arc or incandescent lighting. The operation of Tesla's induction motor required a lower frequency than the 133 Hz common for lighting systems in 1890. 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.
[edit]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.[6] Because the Niagara project was so influential on electric power systems design, 25 Hz prevailed as the North American standard for low-frequency AC.
[edit]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.[7] The oldest continuously-operating commercial hydroelectric power plant in the United States, at Mechanicville, New York, 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.
[edit]Standardization
In the early days of electrification, so many frequencies were used that no one value prevailed (London in 1918 had 10 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 interconection 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, 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.
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 USA, and for railway electrification. In the 1950s, many 25 Hz systems, from the generators right through to household appliances, were converted and standardized. Some 25 Hz generators still exist at the Beck 1 and Rankine generating stations 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 electrical generator power station exist in New Orleans for floodwater pumps [1]. Some of the metre gauge railway lines in Switzerland operate at 16⅔ Hz, which can obtained from the local 50 Hz 3 phase power grid through frequency converters.
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.[8] Converters for production of DC from alternating current were larger and 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 consume 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, the Southern California Edison company had standardized on 50 Hz [9]. 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.[10]
In Mexico, areas operating on 50 Hz grid were converted during the 1970s, uniting the country under 60 Hz.[11]
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.
Utility Frequencies in Use in 1897 in North America [12]
Cycles 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 "increasing 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
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 [13] 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)
Cycles 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.
[edit]Railways
Main article: List of current systems for electric rail traction
Other power frequencies are used. Germany, Austria, Switzerland, Sweden and Norway use traction power networks for railways, distributing single-phase AC at 16.7 Hz[14]. A frequency of 25 Hz is used for the Austrian railway Mariazeller Bahn and some railway systems in New York and Pennsylvania (Amtrak) in the USA. Other 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 generating stations. In the 19th Century frequencies as low as 8 Hz were contemplated for operation of electric railways with commutator motors [1] Some outlets in trains carry the correct voltage, but using the original train network frequency like 16⅔ Hz.
[edit]400 Hz
Frequencies as high as 400 Hz are used in submarines, aerospace, spacecraft and server rooms for computer power and hand-held machine tools. Such high frequencies cannot be economically transmitted long distances, so 400 Hz power systems are usually confined to a building or vehicle. 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. This is an application suitable for switched-mode power supplies.
[edit]Stability
[edit]Long-term stability and clock synchronization
Regulation of power system frequency for timekeeping accuracy was not commonplace until after 1926 and the invention of the electric clock driven by a synchronous motor. Network operators will 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.[15] In the continental European UCTE grid, the deviation between network phase time and UTC is calculated at 08:00 each day in a control center in Switzerland, and the target frequency is then adjusted by up to ±0.02% from 50 Hz as needed, to ensure a long-term frequency average of exactly 3600×24×50 cycles per day is maintained.[16] 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.[17][18] A dynamicdemand.co.uk/grid - Real-time frequency meter for power generation in the United Kingdom is available online. Smaller power systems may not maintain frequency with the same degree of accuracy.
[edit]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 so 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. AGC (automatic generation control) is used to maintain scheduled frequency and interchange power flows. Control systems in power plants 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.
Frequency protection 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.[19][20]
[edit]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. It is usually produced by motor and transformer core laminations vibrating in time with the magnetic field. This hum is often evident in poorly made audio amplifiers as well, where the power supply is inadequately filtered.
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 helps prevent power line hum and magnetic interference from causing visible beat frequencies in the displayed picture of analog receivers, but is of diminishing importance in modern digital display systems.
[edit]See also
Mains electricity
Mains power systems
List of countries with mains power plugs, voltages and frequencies
Power connector
Sunday, December 20, 2009
speech at copenhegen
Following is the text of Shri Jairam Ramesh , Minister of State (independent charge) for Environment & Forests, Government Of India, At the high-level segment of the Un Climate Conference, Copenhagen, 16 December 2009.
“Mr. President, Excellencies, Ladies & Gentlemen,
It is my privilege to speak on behalf of the Government of India. We continue to derive inspiration from the Father of our nation, Mahatma Gandhi who is an icon for the environmental movement everywhere.
India is already and will be even more profoundly impacted by climate change. In many ways, we have the highest vulnerability on multiple dimensions. We have a tremendous obligation to our own people by way of both adaptation and mitigation policies and programmes. That is why we have already announced a number of ambitious measures proactively.
We have a detailed national action plan on climate change with eight focused national missions and twenty four critical initiatives. Under this plan, we have already launched a solar energy mission aimed at 20,000 Mw by 2022 and a domestic market-based mechanism for further stimulating energy efficiency in industry. Other national missions for accelerating afforestation, for promoting sustainable habitats, for expanding sustainable agriculture and for protecting the crucial Himalayan ecosystem are on the anvil. New GHG emission-reducing technologies in coal-based power generation are being deployed on a large-scale. Mandatory fuel efficiency standards in the transport sector will soon become a reality.
We have established our own version of an IPCC comprising more than 120 of our leading scientific and technological institutions to continuously measure, monitor and model the impacts of climate change on different sectors and in different regions of our country. In addition to establishing a nation-wide climate observatory network, we are going to launch our own satellite in 2011 to monitor GHG and aerosol emissions globally.
Derived from our detailed National Action Plan on Climate Change, we are now considering nationally accountable mitigation outcomes in different sectors like industry, energy, transport, building and forests. Over the last decade we have added over 3 million hectares to our forest cover and today our forest cover is sequestering close to 10% of our annual greenhouse gas emissions. We will endeavour to maintain that level.
India has been a major participant in the CDM. If all our projects are approved and implemented as scheduled by 2012, carbon credits amounting to a further 10% of our annual GHG emissions will be available to developed countries to enable them to meet their KP commitments.
We are convinced that a low-carbon strategy is an essential aspect of sustainable development. While we already have one of the lowest emissions intensity of the economy, we will do more. We are targeting a further emissions intensity decline of 20-25% by 2020 on 2005 levels. This is significant given our huge developmental imperatives.
Deeply conscious of our international responsibilities as well, we have already declared that our per capita emissions will never exceed the per capita emissions of the developed countries. We have recently unveiled projected GHG emissions profiles till the year 2030.
Aware of the need for enhanced transparency, we have suggested using the National Communication process, in a format and frequency to be agreed to, as a mechanism to reflect internationally the nature and impact of actions taken domestically. Let me add here that India has probably the most rigorous MRV system that any government can go through – with its democratic Parliament, activist judiciary, vigilant NGOs and watchful media.
We are transforming environmental governance systems. A judicial National Green Tribunal and an executive National Environmental Protection Agency is on the anvil. We have just announced a new generation of national ambient air quality standards that is on par with the strictest in the world.
Our entire approach to this Conference is anchored in the sanctity of the troika--the UNFCCC, the Kyoto Protocol and the Bali Action Plan. We believe that the well-known and widely accepted principles of (i) common but differentiated responsibility; and (ii) historical responsibilities are sacrosanct.
As a global goal, India subscribes to the view that the temperature increase ought not to exceed 2 degrees Celsius by 2050 from mid-19th century levels. But this objective must be firmly embedded in a demonstrably equitable access to atmospheric space, with adequate finance and technology available to all developing countries.
Excellencies, one of the two heads of state to address the first UN Conference on the Environment held in Stockholm thirty seven years back was Mrs. Indira Gandhi – the other being the host Prime Minister. What she said on the historic occasion brought the development agenda into the mainstream of the discourse on environmental concerns. We recall that message and reiterate our resolve to be integral part of the solution to global warming—now and always.”
“Mr. President, Excellencies, Ladies & Gentlemen,
It is my privilege to speak on behalf of the Government of India. We continue to derive inspiration from the Father of our nation, Mahatma Gandhi who is an icon for the environmental movement everywhere.
India is already and will be even more profoundly impacted by climate change. In many ways, we have the highest vulnerability on multiple dimensions. We have a tremendous obligation to our own people by way of both adaptation and mitigation policies and programmes. That is why we have already announced a number of ambitious measures proactively.
We have a detailed national action plan on climate change with eight focused national missions and twenty four critical initiatives. Under this plan, we have already launched a solar energy mission aimed at 20,000 Mw by 2022 and a domestic market-based mechanism for further stimulating energy efficiency in industry. Other national missions for accelerating afforestation, for promoting sustainable habitats, for expanding sustainable agriculture and for protecting the crucial Himalayan ecosystem are on the anvil. New GHG emission-reducing technologies in coal-based power generation are being deployed on a large-scale. Mandatory fuel efficiency standards in the transport sector will soon become a reality.
We have established our own version of an IPCC comprising more than 120 of our leading scientific and technological institutions to continuously measure, monitor and model the impacts of climate change on different sectors and in different regions of our country. In addition to establishing a nation-wide climate observatory network, we are going to launch our own satellite in 2011 to monitor GHG and aerosol emissions globally.
Derived from our detailed National Action Plan on Climate Change, we are now considering nationally accountable mitigation outcomes in different sectors like industry, energy, transport, building and forests. Over the last decade we have added over 3 million hectares to our forest cover and today our forest cover is sequestering close to 10% of our annual greenhouse gas emissions. We will endeavour to maintain that level.
India has been a major participant in the CDM. If all our projects are approved and implemented as scheduled by 2012, carbon credits amounting to a further 10% of our annual GHG emissions will be available to developed countries to enable them to meet their KP commitments.
We are convinced that a low-carbon strategy is an essential aspect of sustainable development. While we already have one of the lowest emissions intensity of the economy, we will do more. We are targeting a further emissions intensity decline of 20-25% by 2020 on 2005 levels. This is significant given our huge developmental imperatives.
Deeply conscious of our international responsibilities as well, we have already declared that our per capita emissions will never exceed the per capita emissions of the developed countries. We have recently unveiled projected GHG emissions profiles till the year 2030.
Aware of the need for enhanced transparency, we have suggested using the National Communication process, in a format and frequency to be agreed to, as a mechanism to reflect internationally the nature and impact of actions taken domestically. Let me add here that India has probably the most rigorous MRV system that any government can go through – with its democratic Parliament, activist judiciary, vigilant NGOs and watchful media.
We are transforming environmental governance systems. A judicial National Green Tribunal and an executive National Environmental Protection Agency is on the anvil. We have just announced a new generation of national ambient air quality standards that is on par with the strictest in the world.
Our entire approach to this Conference is anchored in the sanctity of the troika--the UNFCCC, the Kyoto Protocol and the Bali Action Plan. We believe that the well-known and widely accepted principles of (i) common but differentiated responsibility; and (ii) historical responsibilities are sacrosanct.
As a global goal, India subscribes to the view that the temperature increase ought not to exceed 2 degrees Celsius by 2050 from mid-19th century levels. But this objective must be firmly embedded in a demonstrably equitable access to atmospheric space, with adequate finance and technology available to all developing countries.
Excellencies, one of the two heads of state to address the first UN Conference on the Environment held in Stockholm thirty seven years back was Mrs. Indira Gandhi – the other being the host Prime Minister. What she said on the historic occasion brought the development agenda into the mainstream of the discourse on environmental concerns. We recall that message and reiterate our resolve to be integral part of the solution to global warming—now and always.”
PPP-NHRM
National Rural Health Mission [NRHM] was launched in April 2005 with thrust on creating a fully functional platform for health care at all levels, from the village, the Sub-Centre, the Primary Health Centre, the Community Health Centre, the District Hospital to the District and State levels with the prime objective of providing quality services that are affordable, accessible and accountable. The NRHM Mission document has also articulated the need for Public Private Partnerships. NRHM encourages training and up-gradation of skills for public-private providers wherever such efforts are likely to improve quality of services for the poor.
Some of the examples of successful models of Public Private Partnership under NRHM are: [i] Tamil Nadu Government’s Criteria for Accreditation of Public-Private providers undertaken as part of the Janani Suraksha Yojana (JSY) for institutional delivery. [ii] Franchising, as per agreed standards and costs as attempted by the Surya Clinics of Janani in Bihar, [iii] Yeshasvini Trust Health Insurance partnerships in Karnataka for standard surgeries at agreed costs [iv] Chiranjeevi Scheme of Gujarat to involve private sector Gynaecologists for institutional delivery of Below Poverty Line women, [v] Initiative by Government of West Bengal in partnerships with the private sector for its Mobile Health Clinics, [vi] Outsourcing of diagnostic tests successfully attempted in Bihar and West Bengal [vii] community worker programme of Mitanins, ASHAs and link workers in some States involving private organizations on a very large scale in facilitation, training and resource support. [viii] The successful management of PHCs in Arunachal Pradesh by Karuna Trust, Voluntary Health Association of India and other organizations. [ix] Emergency Medical Relief Programme (EMRI) of Andhra Pradesh.
This information was given by Shri Ghulam Nabi Azad, Union Minister of Health & Family Welfare in a written reply to a question in the Lok Sabha today.
Some of the examples of successful models of Public Private Partnership under NRHM are: [i] Tamil Nadu Government’s Criteria for Accreditation of Public-Private providers undertaken as part of the Janani Suraksha Yojana (JSY) for institutional delivery. [ii] Franchising, as per agreed standards and costs as attempted by the Surya Clinics of Janani in Bihar, [iii] Yeshasvini Trust Health Insurance partnerships in Karnataka for standard surgeries at agreed costs [iv] Chiranjeevi Scheme of Gujarat to involve private sector Gynaecologists for institutional delivery of Below Poverty Line women, [v] Initiative by Government of West Bengal in partnerships with the private sector for its Mobile Health Clinics, [vi] Outsourcing of diagnostic tests successfully attempted in Bihar and West Bengal [vii] community worker programme of Mitanins, ASHAs and link workers in some States involving private organizations on a very large scale in facilitation, training and resource support. [viii] The successful management of PHCs in Arunachal Pradesh by Karuna Trust, Voluntary Health Association of India and other organizations. [ix] Emergency Medical Relief Programme (EMRI) of Andhra Pradesh.
This information was given by Shri Ghulam Nabi Azad, Union Minister of Health & Family Welfare in a written reply to a question in the Lok Sabha today.
Tuesday, December 15, 2009
new states
climate change affect everyone.so solution by everyone.
CDR,ADOPTION TECHNOLOGY,FUND
NEW STATES:
1.ADM N DEVELOPMENT REGIONS
2.VOTORS WILL BE MORE INFORMED
3.INTER-STATE MOVEMENT OF PEOPLE WILL increase
4.all new states-chatis,jhar,utt have more pci than the parent states
5.cost benefit analysis
CDR,ADOPTION TECHNOLOGY,FUND
NEW STATES:
1.ADM N DEVELOPMENT REGIONS
2.VOTORS WILL BE MORE INFORMED
3.INTER-STATE MOVEMENT OF PEOPLE WILL increase
4.all new states-chatis,jhar,utt have more pci than the parent states
5.cost benefit analysis
Saturday, December 12, 2009
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