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  1. Transformer - Wikipedia › wiki › Transformer

    In 1891, Nikola Tesla invented the Tesla coil, an air-cored, dual-tuned resonant transformer for producing very high voltages at high frequency. [77] Audio frequency transformers (" repeating coils ") were used by early experimenters in the development of the telephone .

  2. Very high frequency - Wikipedia › wiki › VHF_Band

    Very high frequency ( VHF) is the ITU designation for the range of radio frequency electromagnetic waves ( radio waves) from 30 to 300 megahertz (MHz), with corresponding wavelengths of ten meters to one meter. Frequencies immediately below VHF are denoted high frequency (HF), and the next higher frequencies are known as ultra high frequency (UHF).

    • 10 to 1 m
    • 30 MHz to 300 MHz
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    How does a high frequency transformer design work?

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  4. Variable-frequency transformer - Wikipedia › wiki › Variable-frequency_transformer

    A variable-frequency transformer ( VFT) is used to transmit electricity between two ( asynchronous or synchronous) 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 ...

  5. High frequency - Wikipedia › wiki › High_frequency

    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 meters).

    • 100 to 10 m
    • 3 to 30 MHz
  6. Transformer types - Wikipedia › wiki › Transformer_types

    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.

  7. Transformer | Wikitronics | Fandom › wiki › Transformer
    • History
    • Basic Principles
    • Practical Considerations
    • Transformer Types and Uses
    • Construction
    • External Links

    Michael Faraday built the first transformer in 1831, although he used it only to demonstrate the principle of electromagnetic induction and did not foresee its practical uses. Lucien Gaulard and John Dixon Gibbs, who first exhibited a device called a 'secondary generator' in London in 1882 and then sold the idea to American company Westinghouse. This may have been the first practical power transformer. They also exhibited the invention in Turin in 1884, where it was adopted for an electric lighting system. Their early devices used an open iron core, which was soon abandoned in favour of a more efficient circular core with a closed magnetic path. Russian engineer Pavel Yablochkov in 1876 invented a lighting system based on a set of induction coils, where primary windings were connected to a source of alternating current and secondary windings could be connected to several "electric candles". As the patent said, such a system "allows to provide separate supply to several lighting fixt...

    Coupling by mutual induction

    The principles of the transformer are illustrated by consideration of a hypothetical ideal transformer consisting of two windings of zero resistance around a core of negligible reluctance. A voltage applied to the primary winding causes a current, which develops a magnetomotive force (MMF) in the core. The current required to create the MMF is termed the magnetising current; in the ideal transformer it is considered to be negligible. The MMF drives flux around the magnetic circuitof the core....

    Under load

    If a load impedance is connected to the secondary winding, a current will flow in the secondary circuit so created. The current develops an MMF over the secondary winding in opposition to that of the primary winding, so acting to cancel the flux in the core. The now decreased flux reduces the primary EMF, causing current in the primary circuit to increase to exactly offset the effect of the secondary MMF, and returning the flux to its former value. The core flux thus remains the same regardle...

    Circuit symbols

    Standard symbols

    Effect of frequency

    The time-derivative term in Faraday's Law implies that the flux in the core is the integral of the applied voltage. An ideal transformer would, at least hypothetically, work under direct-current excitation, with the core flux increasing linearly with time. In practice, the flux would rise very rapidly to the point where magnetic saturationof the core occurred and the transformer would cease to function as such. All practical transformers must therefore operate under alternating (or pulsed) cu...

    Energy losses

    An ideal transformer would have no energy losses, and would therefore be 100% efficient. Despite the transformer being amongst the most efficient of electrical machines, with experimental models using superconducting windings achieving efficiencies of 99.85%, energy is dissipated in the windings, core, and surrounding structures. Larger transformers are generally more efficient, and those rated for electricity distribution usually perform better than 95%.A small transformer such as a plug-in...

    A variety of specialised transformer designs has been created to fulfil certain engineering applications. The numerous applications to which transformers are adapted lead them to be classified in many ways: 1. By power level: from a fraction of a volt-ampere(VA) to over a thousand MVA; 2. By frequency range: power-, audio- or radio frequency; 3. By voltage class: from a few volts to hundreds of kilovolts; 4. By cooling type: air cooled, oil filled, fan cooled, or water cooled; 5. By application function: such as power supply, impedance matching or circuit isolation; 6. By end purpose: distribution, rectifier, arc furnace, amplifier output; 7. By winding turns ratio: step-up, step-down, isolating (near equal ratio), variable.


    The wire of the adjacent turns in a coil, and in the different windings, must be electrically insulated from each other. The wire used is generally magnet wire. Magnet wire is a copper wire with a coating of varnish or some other synthetic coating. Transformers for years have used Formvarwire, which is a varnished type of magnet wire. The conducting material used for the winding depends upon the application. Small power and signal transformers are wound with solid copper wire, insulated usual...

    Winding insulation

    The turns of the windings must be insulated from each other to ensure that the current travels through the entire winding. The potential difference between adjacent turns is usually small, so that enamel insulation may suffice for small power transformers. Supplemental sheet or tape insulation is usually employed between winding layers in larger transformers. The transformer may also be immersed in transformer oil that provides further insulation. Although the oil is primarily used to cool th...


    Where transformers are intended for minimum electrostatic coupling between primary and secondary circuits, an electrostatic shield can be placed between windings to reduce the capacitance between primary and secondary windings. The shield may be a single layer of metal foil, insulated where it overlaps to prevent it acting as a shorted turn, or a single layer winding between primary and secondary. The shield is connected to earth ground. Transformers may also be enclosed by magnetic shields,...

    Inside Transformersfrom Denver University
    Understanding Transformers: Characteristics and Limitationsfrom Conformity Magazine
    DMOZ: Business: Electronics and Electrical: Substation and TransmissionTransformers for the Utility sector
  8. Wikipedia | TRANSFORMERS › category › wikipedia

    Special high voltage pulse transformers are also used to generate high power pulses for radar, particle accelerators, or other high energy pulsed power applications. ————————– RF TRANSFORMERS. Air-core transformers These are used for high frequency work. The lack of a core means very low inductance.

  9. Design of High-density Transformers for High-frequency High ... › bitstream › handle

    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

  10. Transformer wiki | TheReaderWiki › en › Transformer
    • Principles
    • Construction
    • Classification Parameters
    • Applications
    • History

    Ideal transformer

    An ideal transformer is a theoretical linear transformer that is lossless and perfectly coupled. Perfect coupling implies infinitely high core magnetic permeability and winding inductances and zero net magnetomotive force (i.e. ipnp - isns = 0).[c] A varying current in the transformer's primary winding attempts to create a varying magnetic flux in the transformer core, which is also encircled by the secondary winding. This varying flux at the secondary winding induces a varying electromotive...

    Real transformer

    The ideal transformer model neglects the following basic linear aspects of real transformers: (a) Core losses, collectively called magnetizing current losses, consisting of 1. Hysteresislosses due to nonlinear magnetic effects in the transformer core, and 2. Eddy currentlosses due to joule heating in the core that are proportional to the square of the transformer's applied voltage. (b) Unlike the ideal model, the windings in a real transformer have non-zero resistances and inductances associa...

    Transformer EMF equation

    If the flux in the core is purely sinusoidal, the relationship for either winding between its rms voltage Erms of the winding, and the supply frequency f, number of turns N, core cross-sectional area a in m2 and peak magnetic flux density Bpeak in Wb/m2or T (tesla) is given by the universal EMF equation: 1. E rms = 2 π f N a B peak 2 ≈ 4.44 f N a B peak {\\displaystyle E_{\\text{rms}}={\\frac {2\\pi fNaB_{\\text{peak}}}{\\sqrt {2}}}\\approx 4.44fNaB_{\\text{peak}}}


    Core form = core type; shell form = shell type Closed-core transformers are constructed in 'core form' or 'shell form'. When windings surround the core, the transformer is core form; when windings are surrounded by the core, the transformer is shell form. Shell form design may be more prevalent than core form design for distribution transformer applications due to the relative ease in stacking the core around winding coils. Core form design tends to, as a general rule, be more economical, and...


    The electrical conductor used for the windings depends upon the application, but in all cases the individual turns must be electrically insulated from each other to ensure that the current travels throughout every turn. For small transformers, in which currents are low and the potential difference between adjacent turns is small, the coils are often wound from enamelled magnet wire. Larger power transformers may be wound with copper rectangular strip conductors insulated by oil-impregnated pa...


    It is a rule of thumb that the life expectancy of electrical insulation is halved for about every 7 °C to 10 °C increase in operating temperature (an instance of the application of the Arrhenius equation). Small dry-type and liquid-immersed transformers are often self-cooled by natural convection and radiation heat dissipation. As power ratings increase, transformers are often cooled by forced-air cooling, forced-oil cooling, water-cooling, or combinations of these. Large transformers are fil...

    Transformers can be classified in many ways, such as the following: 1. Power rating: From a fraction of a volt-ampere (VA) to over a thousand MVA. 2. Duty of a transformer: Continuous, short-time, intermittent, periodic, varying. 3. Frequency range: Power-frequency, audio-frequency, or radio-frequency. 4. Voltage class: From a few volts to hundreds of kilovolts. 5. Cooling type: Dry or liquid-immersed; self-cooled, forced air-cooled;forced oil-cooled, water-cooled. 6. Application: power supply, impedance matching, output voltage and current stabilizer, pulse, circuit isolation, power distribution, rectifier, arc furnace, amplifier output, etc.. 7. Basic magnetic form: Core form, shell form, concentric, sandwich. 8. Constant-potential transformer descriptor: Step-up, step-down, isolation. 9. General winding configuration: By IEC vector group, two-winding combinations of the phase designations delta, wye or star, and zigzag; autotransformer, Scott-T 10. Rectifier phase-shift winding c...

    Various specific electrical application designs require a variety of transformer types. Although they all share the basic characteristic transformer principles, they are customized in construction or electrical properties for certain installation requirements or circuit conditions. In electric power transmission, transformers allow transmission of electric power at high voltages, which reduces the loss due to heating of the wires. This allows generating plants to be located economically at a distance from electrical consumers.All but a tiny fraction of the world's electrical power has passed through a series of transformers by the time it reaches the consumer. In many electronic devices, a transformer is used to convert voltage from the distribution wiring to convenient values for the circuit requirements, either directly at the power line frequency or through a switch mode power supply. Signal and audio transformers are used to couple stages of amplifiers and to match devices such...

    Discovery of induction

    Electromagnetic induction, the principle of the operation of the transformer, was discovered independently by Michael Faraday in 1831 and Joseph Henry in 1832. Only Faraday furthered his experiments to the point of working out the equation describing the relationship between EMF and magnetic flux now known as Faraday's law of induction: 1. | E | = | d Φ B d t | , {\\displaystyle |{\\mathcal {E}}|=\\left|{{\\mathrm {d} \\Phi _{\\text{B}}} \\over \\mathrm {d} t}\\right|,} where | E | {\\displaystyle |{\\m...

    Induction coils

    The first type of transformer to see wide use was the induction coil, invented by Rev. Nicholas Callan of Maynooth College, Ireland in 1836. He was one of the first researchers to realize the more turns the secondary winding has in relation to the primary winding, the larger the induced secondary EMF will be. Induction coils evolved from scientists' and inventors' efforts to get higher voltages from batteries. Since batteries produce direct current (DC) rather than AC, induction coils relied...

    First alternating current transformers

    By the 1870s, efficient generators producing alternating current (AC) were available, and it was found AC could power an induction coil directly, without an interrupter. In 1876, Russian engineer Pavel Yablochkov invented a lighting system based on a set of induction coils where the primary windings were connected to a source of AC. The secondary windings could be connected to several 'electric candles'(arc lamps) of his own design. The coils Yablochkov employed functioned essentially as tran...

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