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DFIG
Doubly-fed electric machines also slip-ring generators are electric motors or electric generators, where both the field magnet windings and armature windings are separately connected to equipment outside the machine. By feeding adjustable frequency AC power to the field windings, the magnetic field can be made to rotate, allowing variation in motor or generator speed. This is useful, for instance, for generators used in wind turbines. DFIG-based wind turbines, because of their flexibility and ability to control active and reactive power, are almost the most interesting wind turbine technology. Introduction Doubly fed electrical generators are similar to AC electrical generators, but have additional features which allow them to run at speeds slightly above or below their natural synchronous speed. This is useful for large variable speed wind turbines, because wind speed can change suddenly. When a gust of wind hits a wind turbine, the blades try to speed ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
DFIG In Wind Turbine
Doubly-fed electric machines also slip-ring generators are electric motors or electric generators, where both the field magnet windings and armature windings are separately connected to equipment outside the machine. By feeding adjustable frequency AC power to the field windings, the magnetic field can be made to rotate, allowing variation in motor or generator speed. This is useful, for instance, for generators used in wind turbines. DFIG-based wind turbines, because of their flexibility and ability to control active and reactive power, are almost the most interesting wind turbine technology. Introduction Doubly fed electrical generators are similar to AC electrical generators, but have additional features which allow them to run at speeds slightly above or below their natural synchronous speed. This is useful for large variable speed wind turbines, because wind speed can change suddenly. When a gust of wind hits a wind turbine, the blades try to speed ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Wound-rotor Doubly-fed Electric Machine
Doubly-fed electric machines also slip-ring generators are electric motors or electric generators, where both the field magnet windings and armature windings are separately connected to equipment outside the machine. By feeding adjustable frequency AC power to the field windings, the magnetic field can be made to rotate, allowing variation in motor or generator speed. This is useful, for instance, for generators used in wind turbines. DFIG-based wind turbines, because of their flexibility and ability to control active and reactive power, are almost the most interesting wind turbine technology. Introduction Doubly fed electrical generators are similar to AC electrical generators, but have additional features which allow them to run at speeds slightly above or below their natural synchronous speed. This is useful for large variable speed wind turbines, because wind speed can change suddenly. When a gust of wind hits a wind turbine, the blades try to spee ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Variable Speed Wind Turbine
A variable speed wind turbine is one which is specifically designed to operate over a wide range of rotor speeds. It is in direct contrast to fixed speed wind turbine where the rotor speed is approximately constant. The reason to vary the rotor speed is to capture the maximum aerodynamic power in the wind, as the wind speed varies. The aerodynamic efficiency, or coefficient of power, C_p for a fixed blade pitch angle is obtained by operating the wind turbine at the optimal tip-speed ratio as shown in the following graph. Tip-speed ratio is given by the following expression, \lambda = \frac where \omega is the rotor speed (in radians per second), R is the radius of the rotor, and v is the wind speed. As the wind speed varies, the rotor speed must be varied to maintain peak efficiency. Background Before the need to connect wind turbines to the grid, turbines were fixed-speed. This was not a problem because turbines did not have to be synchronized with the frequency of the g ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Field Winding
A field coil is an electromagnet used to generate a magnetic field in an electro-magnetic machine, typically a rotating electrical machine such as a motor or generator. It consists of a coil of wire through which a current flows. In a rotating machine, the field coils are wound on an iron magnetic core which guides the magnetic field lines. The magnetic core is in two parts; a stator which is stationary, and a rotor, which rotates within it. The magnetic field lines pass in a continuous loop or magnetic circuit from the stator through the rotor and back through the stator again. The field coils may be on the stator or on the rotor. The magnetic path is characterized by ''poles'', locations at equal angles around the rotor at which the magnetic field lines pass from stator to rotor or vice versa. The stator (and rotor) are classified by the number of poles they have. Most arrangements use one field coil per pole. Some older or simpler arrangements use a single field coil w ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Chinese Society For Electrical Engineering
The Chinese Society for Electrical Engineering (CSEE; ) is a professional organization for electrical engineers in China. It was founded in 1934 in Shanghai, as the Chinese Society for Electrical Engineers. , its members include over 120,000 individual engineers and over 1000 organizations.. The CSEE is a member of the China Association for Science and Technology (CAST). It includes 32 provincial societies, 32 study committees on subtopics within electrical engineering, and 8 working committees. Together with the electrical engineering organizations of several other Asian countries, it is a sponsor of the annual International Conference of Electrical Engineering. Its flagship academic journal, founded in 1964 and produced in cooperation with CAST and the China Electric Power Research Institute, is the ''Proceedings of the Chinese Society for Electrical Engineering''.. See also *List of engineering societies An engineering society is a professional organization for engineers of vari ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Slip Ring
A slip ring is an electromechanical device that allows the transmission of power and electrical signals from a stationary to a rotating structure. A slip ring can be used in any electromechanical system that requires rotation while transmitting power or signals. It can improve mechanical performance, simplify system operation and eliminate damage-prone wires dangling from movable joints. Also called rotary electrical interfaces, rotating electrical connectors, collectors, swivels, or electrical rotary joints, these rings are commonly found in slip ring motors, electrical generators for alternating current (AC) systems and alternators and in packaging machinery, cable reels, and wind turbines. They can be used on any rotating object to transfer power, control circuits, or analog or digital signals including data such as those found on aerodrome beacons, rotating tanks, power shovels, radio telescopes, telemetry systems, heliostats or ferris wheels. A slip ring (in electrical eng ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Induction Generator
An induction generator or ''asynchronous generator'' is a type of alternating current (AC) electrical generator that uses the principles of induction motors to produce electric power. Induction generators operate by mechanically turning their rotors faster than synchronous speed. A regular AC induction motor usually can be used as a generator, without any internal modifications. Because they can recover energy with relatively simple controls, induction generators are useful in applications such as mini hydro power plants, wind turbines, or in reducing high-pressure gas streams to lower pressure. An induction generator draws reactive excitation current from an external source. Induction generators have an AC rotor and cannot bootstrap using residual magnetization to black start a de-energized distribution system as synchronous machines do. Power factor correcting capacitors can be added externally to neutralize a constant amount of the variable reactive excitation current. After s ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Insulated-gate Bipolar Transistor
An insulated-gate bipolar transistor (IGBT) is a three-terminal power semiconductor device primarily used as an electronic switch, which, as it was developed, came to combine high efficiency and fast switching. It consists of four alternating layers (P–N–P–N) that are controlled by a metal–oxide–semiconductor (MOS) gate structure. Although the structure of the IGBT is topologically the same as a thyristor with a "MOS" gate ( MOS-gate thyristor), the thyristor action is completely suppressed, and only the transistor action is permitted in the entire device operation range. It is used in switching power supplies in high-power applications: variable-frequency drives (VFDs), electric cars, trains, variable-speed refrigerators, lamp ballasts, arc-welding machines, induction hobs, and air conditioners. Since it is designed to turn on and off rapidly, the IGBT can synthesize complex waveforms with pulse-width modulation and low-pass filters, so it is also used in switching ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cycloconverter
A cycloconverter (CCV) or a cycloinverter converts a constant amplitude, constant frequency Alternating current, AC waveform to another AC waveform of a lower frequency by synthesizing the output waveform from segments of the AC supply without an intermediate DC link ( and ). There are two main types of CCVs, circulating current type or blocking mode type, most commercial high power products being of the blocking mode type. Characteristics Whereas phase-controlled silicon-controlled rectifier, SCR switching devices can be used throughout the range of CCVs, low cost, low-power TRIAC-based CCVs are inherently reserved for resistive load applications. The amplitude and frequency of converters' output voltage are both variable. The output to input frequency ratio of a three-phase CCV must be less than about one-third for circulating current mode CCVs or one-half for blocking mode CCVs.Bose (2006), p. 153 Output waveform quality improves as the ''pulse number'' of switching-device bri ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Mercury-arc Valve
A mercury-arc valve or mercury-vapor rectifier or (UK) mercury-arc rectifier is a type of electrical rectifier used for converting high-voltage or high-current alternating current (AC) into direct current (DC). It is a type of cold cathode gas-filled tube, but is unusual in that the cathode, instead of being solid, is made from a pool of liquid mercury and is therefore self-restoring. As a result mercury-arc valves, when used as intended, are far more robust and durable and can carry much higher currents than most other types of gas discharge tube. Some examples have been in continuous service, rectifying 50 ampere currents for decades. Invented in 1902 by Peter Cooper Hewitt, mercury-arc rectifiers were used to provide power for industrial motors, electric railways, streetcars, and electric locomotives, as well as for radio transmitters and for high-voltage direct current (HVDC) power transmission. They were the primary method of high power rectification before the advent of semi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Arthur Scherbius
Arthur Scherbius (30 October 1878 – 13 May 1929) was a German electrical engineer who invented the mechanical cipher Enigma machine. He patented the invention and later sold the machine under the brand name Enigma. Scherbius offered unequalled opportunities and showed the importance of cryptography to both military and civil intelligence. Biography Early life and work Scherbius was born in Frankfurt am Main, Germany. His father was a businessman. He studied electrical engineering at the Technical University Munich and then went on to study at the Leibniz University Hannover, finishing in March 1903. The next year he completed a dissertation entitled "Proposal for the Construction of an Indirect Water Turbine Governor" and was awarded a doctorate in engineering (Dr.-Eng.). Career Scherbius subsequently worked for a number of electrical firms in Germany and Switzerland. In 1918 he founded the firm of Scherbius & Ritter. He made a number of inventions including asynchronou ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
