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In 1891, Nikola Tesla invented the Tesla coil, an air-cored, dual-tuned resonant transformer for producing very high voltages at high frequency. Audio frequency transformers ("repeating coils") were used by early experimenters in the development of the telephone.  See also
There are several types of transformer used in radio frequency (RF) work. Laminated steel is not suitable for RF. Air-core transformer. These are used for high frequency work. The lack of a core means very low inductance. All current excites current and induces secondary voltage which is proportional to the mutual inductance.
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What is a variable-frequency transformer?
What is a large power transformer?
What is a high frequency radio wave?
What causes a power transformer to overexcitate?
A variable-frequency transformer is used to transmit electricity between two alternating current frequency domains. The VFT is a relatively recent development. Most asynchronous grid inter-ties use high-voltage direct current converters, while synchronous grid inter-ties are connected by lines and "ordinary" transformers, but without the ability to control power flow between the systems. It can be thought of as a very high power synchro, or a rotary converter acting as a frequency changer, which
An Oudin coil, also called an Oudin oscillator or Oudin resonator, is a resonant transformer circuit that generates very high voltage, high frequency alternating current electricity at low current levels, used in the obsolete medical field of electrotherapy around the turn of the 20th century. It is very similar to the earlier Tesla coil, patented in 1891, with the difference being that the Oudin coil was connected as an autotransformer. It was invented in 1893 by French physician Paul Marie Oud
Very high frequency is the ITU designation for the range of radio frequency electromagnetic waves from 30 to 300 megahertz, with corresponding wavelengths of ten meters to one meter. Frequencies immediately below VHF are denoted high frequency, and the next higher frequencies are known as ultra high frequency. VHF radio waves propagate mainly by line-of-sight, they are blocked by hills and mountains, although due to refraction they can travel somewhat beyond the visual horizon out to about 160 k
- Propagation characteristics
High frequency is the ITU designation for the range of radio frequency electromagnetic waves between 3 and 30 megahertz. It is also known as the decameter band or decameter wave as its wavelengths range from one to ten decameters. Frequencies immediately below HF are denoted medium frequency, while the next band of higher frequencies is known as the very high frequency band. The HF band is a major part of the shortwave band of frequencies, so communication at these frequencies is often called sh
The dominant means of long-distance communication in this band is skywave propagation, in which radio waves directed at an angle into the sky refract back to Earth from layers of ionized atoms in the ionosphere. By this method HF radio waves can travel beyond the horizon, around the curve of the Earth, and can be received at intercontinental distances. However, suitability of this portion of the spectrum for such communication varies greatly with a complex combination of factors: 1. Sunlight/dar
The main users of the high frequency spectrum are: 1. Military and governmental communication systems 2. Aviation air-to-ground communications 3. Amateur radio 4. Shortwave international and regional broadcasting 5. Maritime sea-to-shore and ship-to-ship services 6. Over-the-horizon radar systems 7. Global Maritime Distress and Safety System communication 8. Citizen's Band Radio services worldwide The high frequency band is very popular with amateur radio operators, who can take advantage of dir
The most common antennas in this band are wire antennas such as wire dipoles and the rhombic antenna; in the upper frequencies, multielement dipole antennas such as the Yagi, quad, and log-periodic antennas. Powerful shortwave broadcasting stations often use large wire curtain arrays. Antennas for transmitting skywaves are typically made from horizontal dipoles or bottom-fed loops, both of which emit horizontally polarized waves. The preference for horizontally polarized transmission is because
- 100 to 10 m
- 3 to 30 MHz
In 1891 Nikola Tesla invented the Tesla coil, an air-cored, dual-tuned resonant transformer for generating very high voltages at high frequency. Audio frequency transformers (at the time called repeating coils) were used by the earliest experimenters in the development of the telephone. While new technologies have made transformers in some electronics applications obsolete, transformers are still found in many electronic devices.
- Basic Principles
- Practical Considerations
- Transformer Designs
- Uses of Transformers
- See Also
A simple single phase transformer consists of two electrical conductors called the primary winding and the secondary winding. The primary is fed with a varying (alternating or pulsed continuous) electric current which creates a varying magnetic field around the conductor. According to the principle of mutual inductance, the secondary, which is placed in this varying magnetic field, will develop an electromotive force or EMF. If the ends of the secondary are connected together to form an elect...
Consider the following two laws: 1. According to the law of conservation of energy, the powerdelivered by a transformer cannot exceed the power fed into it. 2. The power dissipated in a load at any instant is equal to the product of the voltage across it and the (in phase) current passing through it (see also Ohm's law). It follows from the above two laws that a transformer is not an amplifier. If the transformer is used to change power from one voltage to another, the magnitudes of the curre...
Those credited with the invention of the transformer include: 1. Michael Faraday, who invented an 'induction ring' on August 29, 1831. This was the first transformer, although Faraday used it only to demonstrate the principle of electromagnetic inductionand did not foresee the use to which it would eventually be put. 2. Lucien Gaulard and John Dixon Gibbs, who first exhibited a device called a 'secondary generator' in London in 1881 and then sold the idea to American company Westinghouse. This may have been the first practical power transformer, but was not the first transformer of any kind. They also exhibited the invention in Turinin 1884, where it was adopted for an electric lighting system. Their early devices used a linear iron core, which was later abandoned in favour of a more efficient circular core. 3. William Stanley, an engineer for Westinghouse, who built the first practical device in 1885 after George Westinghouse bought Gaulard and Gibbs' patents. The core was made fro...
Transformers come in a range of sizes from a thumbnail-sized coupling transformer hidden inside a stage microphoneto gigawatt units used to interconnect large portions of national power grids, all operating with the same basic principles and with many similarities in their parts. A rough classification of transformers by the power handled in the circuit, in watts (or, more accurately, VA (volt amperes)): 1. Up to 1 watt: Signal transformers, interstage coupling 2. 1 - 1000 watts: Small power...
An ideal transformer would have no loss, and would therefore be 100% efficient. However, the coils of a real transformer have resistance. When modeling a real transformer the resistance can be considered as existing in series with the winding of an ideal transformer. Large power transformers are often more than 98% efficient, in terms of energy supplied to the primary winding of the transformer and coupled to the secondary. The remaining 2% (or less) of the input energy is lost to: 1. 1.1. Wi...
High frequency operation
The universal transformer emf equation indicates that at higher frequency, the core flux density will be lower for a given voltage. This implies that a core can have a smaller cross-sectional area and thus be physically more compact without reaching saturation. It is for this reason that the aircraft manufacturers and the military use 400 hertz supplies. They are less concerned with efficiency, which is lower at higher frequencies (mostly due to increased hysteresis losses), but are more conc...
A transformer usually has: 1. two or more insulated windings, to carry current 2. a core, in which the mutual magnetic field couplesthe windings. In transformers designed to operate at low frequencies, the windings are usually formed around an iron or steel core. This helps to confine the magnetic field within the transformer and increase its efficiency, although the presence of the core causes energy losses. Transformers made to operate at high frequencies may use other lower loss materials, or may use an air core. Power transformers are further classified by the exact arrangement of the core and windings as "shell type", "core type" and also by the number of "limbs" that carry the flux (3, 4 or 5 for a 3-phase transformer). The differences in the performance of each of these types, while of continuing interest to specialists, is perhaps more detail than is appropriate for a general encyclopedia.
An autotransformerhas only a single winding, which is tapped at some point along the winding. AC or pulsed DC power is applied across a portion of the winding, and a higher (or lower) voltage is produced across another portion of the same winding. Autotransformers are used to compensate for voltage drop in a distribution system or for matching two transmission voltages, for example 115 kV and 138 kV. For voltage ratios not exceeding about 3:1, an autotransformer is less costly, lighter, small...
For three-phase power, three separate single-phase transformers can be used, or all three phases can be connected to a single polyphase transformer. The three primary windings are connected together and the three secondary windings are connected together. The most common connections are Y-Δ, Δ-Y, Δ-Δ and Y-Y. If a winding is connected to earth (grounded) the earth connection point is usually the center point of a Y winding. There are many possible configurations that may involve more or fewer...
A resonant transformer is one that operates at the resonant frequency of one or more of its coils. The resonant coil, usually the secondary, acts as an inductor, and is connected in series with a capacitor. If the primary coil is driven by a periodic source of alternating current, such as a square or sawtooth wave, each pulse of current helps to build up an oscillation in the secondary coil. Due to resonance, a very high voltage can develop across the secondary, until it is limited by some pr...Electric power transmission over long distances. The simplicity, reliability, and economy of conversion of voltages by stationary transformers was the principal factor in the selection of alternati...High-voltage direct-current HVDCpower transmission systemsLarge, specially constructed power transformers are used for electric arc furnaces used in steelmaking.Rotating transformers are designed so that one winding turns while the other remains stationary. A common use was the video head system as used in VHS and Beta video tape players. These can pass po...
Template:Wikibookspar 1. Main : Distributed generation, Electronic power supply, Electronics, Inductor, Pickup, Electrical network, Electricity distribution, Wet transformer, Electronics topics 2. Circuits: Ballast, Clamp meter, Repeating coil, Inverter (electrical), Ignition system, Electricity generation, Linear variable differential transformer, Neon signage, Regulator, Electrical substation, Switched-mode power supply, Technological applications of superconductivity, Tesla coil, Transducer 3. Electromagnetism: Alternating current, Electric power, Electric power transmission, Electromagnetic induction, Equivalent series resistance, High-voltage direct current, Impedance matching, Inductive coupling, Potential difference, Skin effect, Leakage inductance, Superconductivity 4. People: Ottó Bláthy, Miksa Déri, John Ambrose Fleming, Otto A. Knopp, William Stanley, Nikola Tesla, Milan Vidmar, George Westinghouse, Károly Zipernowsky 5. Other: DI unit, Polychlorinated biphenyl, Stafford,...
Design of High-density Transformers for High-frequency High-power Converters Wei Shen ABSTRACT Moore’s Law has been used to describe and predict the blossom of IC industries, so increasing the data density is clearly the ultimate goal of all technological development. If the power density of power electronics converters can be analogized to
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