power transformerelectrical transformerprimary windingsecondary windingstep-up transformertaptransformersAC transformerideal transformerelectrical transformers
A transformer is a passive electrical device that transfers electrical energy from one electrical circuit to one or more circuits.wikipedia
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Faraday's law of induction

Faraday's lawMaxwell–Faraday equationelectromagnetic induction
Faraday's law of induction discovered in 1831 described the induced voltage effect in any coil due to changing magnetic flux encircled by the coil.
It is the fundamental operating principle of transformers, inductors, and many types of electrical motors, generators and solenoids.

Isolation transformer

for an isolation transformer a = 1.
An isolation transformer is a transformer used to transfer electrical power from a source of alternating current (AC) power to some equipment or device while isolating the powered device from the power source, usually for safety reasons.

Electromotive force

EMFelectromotive force (EMF)
A varying current in any one coil of the transformer produces a varying magnetic flux, which, in turn, induces a varying electromotive force across any other coils wound around the same core.
Devices that can provide emf include electrochemical cells, thermoelectric devices, solar cells, photodiodes, electrical generators, transformers and even Van de Graaff generators.

Leakage inductance

leakage fluxleakage reactanceleakage
Such flux is termed leakage flux, and results in leakage inductance in series with the mutually coupled transformer windings.
Leakage inductance derives from the electrical property of an imperfectly-coupled transformer whereby each winding behaves as a self-inductance in series with the winding's respective ohmic resistance constant.

Eddy current

eddy currentseddyeddy-current
Hysteresis and eddy current losses are constant at all load levels and dominate at no load, while winding loss increases as load increases.
They can be induced within nearby stationary conductors by a time-varying magnetic field created by an AC electromagnet or transformer, for example, or by relative motion between a magnet and a nearby conductor.

Railway electrification system

electrifiedelectrificationelectric railway
Conversely, frequencies used for some railway electrification systems were much lower (e.g. 16.7 Hz and 25 Hz) than normal utility frequencies (50–60 Hz) for historical reasons concerned mainly with the limitations of early electric traction motors.
The railway usually provides its own distribution lines, switches, and transformers.

Electric power transmission

transmissionpower linespower line
Since the invention of the first constant-potential transformer in 1885, transformers have become essential for the transmission, distribution, and utilization of alternating current electric power.
These networks use components such as power lines, cables, circuit breakers, switches and transformers.

Open-circuit test

no loadOpen circuit testopen-circuit
Transformer equivalent circuit impedance and transformer ratio parameters can be derived from the following tests: open-circuit test, short-circuit test, winding resistance test, and transformer ratio test.
The open-circuit test, or "no-load test", is one of the methods used in electrical engineering to determine the no-load impedance in the excitation branch of a transformer.

Magnetic core

core lossiron coresoft iron
A magnetic core is a piece of magnetic material with a high magnetic permeability used to confine and guide magnetic fields in electrical, electromechanical and magnetic devices such as electromagnets, transformers, electric motors, generators, inductors, magnetic recording heads, and magnetic assemblies.

Flyback transformer

line output transformerflybackflyback coils
A flyback transformer (FBT), also called a line output transformer (LOPT), is a special type of electrical transformer.

Electrical resistance and conductance

resistanceelectrical resistanceconductance
In other cases, such as a transformer, diode or battery, V and I are not directly proportional.

Utility frequency

50 Hzfrequencymains frequency
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.

Joule heating

resistive heatingohmic heatingJoule's law
However, in applications where heating is an unwanted by-product of current use (e.g., load losses in electrical transformers) the diversion of energy is often referred to as resistive loss.

Short-circuit test

short circuit testshort circuitshort-circuited
Transformer equivalent circuit impedance and transformer ratio parameters can be derived from the following tests: open-circuit test, short-circuit test, winding resistance test, and transformer ratio test.
The purpose of a short-circuit test is to determine the series branch parameters of the equivalent circuit of a transformer.

Mains hum

humbuckinghum60-cycle hum
Mains hum may also be heard coming from powerful electric power grid equipment such as utility transformers, caused by mechanical vibrations induced by magnetostriction in magnetic core.

Inrush current

surge currentFull load currentInrush currents
When power is then reapplied, the residual field will cause a high inrush current until the effect of the remaining magnetism is reduced, usually after a few cycles of the applied AC waveform.
Alternating-current electric motors and transformers may draw several times their normal full-load current when first energized, for a few cycles of the input waveform.

Electrical steel

silicon steelgrain-oriented electrical steelelectrical steels
Designing energy efficient transformers for lower loss requires a larger core, good-quality silicon steel, or even amorphous steel for the core and thicker wire, increasing initial cost.
These strips are cut to shape to make laminations which are stacked together to form the laminated cores of transformers, and the stator and rotor of electric motors.

Polarity (mutual inductance)

Dot conventionpolarity
A dot convention is often used in transformer circuit diagrams, nameplates or terminal markings to define the relative polarity of transformer windings.
In electrical engineering, dot marking convention, or alphanumeric marking convention, or both, can be used to denote the same relative instantaneous polarity of two mutually inductive components such as between transformer windings.

Energy efficient transformer

Designing energy efficient transformers for lower loss requires a larger core, good-quality silicon steel, or even amorphous steel for the core and thicker wire, increasing initial cost.
In a typical power distribution grid, electric transformer power loss typically contributes to about 40-50% of the total transmission and distribution loss.


Two (or more) inductors in proximity that have coupled magnetic flux (mutual inductance) form a transformer, which is a fundamental component of every electric utility power grid.


remanentremanent magnetizationremanent magnetism
A steel core's remanence means that it retains a static magnetic field when power is removed.
In transformers, electric motors and generators a large residual magnetization is not desirable (see also electrical steel) as it is an unwanted contamination, for example a magnetization remaining in an electromagnet after the current in the coil is turned off.

Voltage regulation

regulationregulation of the voltage
It is not directly a power loss, but results in inferior voltage regulation, causing the secondary voltage not to be directly proportional to the primary voltage, particularly under heavy load.
• a load tap changer (LTC) at the substation transformer, which changes the turns ratio in response to load current and thereby adjusts the voltage supplied at the sending end of the feeder;

Magnet wire

Enameled wireenamelenameled
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.
It is used in the construction of transformers, inductors, motors, generators,

Switched-mode power supply

switched-mode power suppliesswitching power suppliesSwitched-mode power supply applications
The development of switching power semiconductor devices made switch-mode power supplies viable, to generate a high frequency, then change the voltage level with a small transformer.
This boost converter acts like a step-up transformer for DC signals.

Center tap

Volts Center Tappedcenter-tappedcenter-tapped transformer
A center-tapped transformer is often used in the output stage of an audio power amplifier in a push-pull circuit.
In electronics, a center tap (CT) is a contact made to a point halfway along a winding of a transformer or inductor, or along the element of a resistor or a potentiometer.