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Transformer

Transformer is a engineering topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Transformer rather than just read about it. In short: In electrical engineering, a transformer is a passive component that transfers electrical energy from one electrical circuit to another circuit, or multiple circuits. A varying current in any coil of the transformer produces a varying magnetic flux in the transformer's core, which induces a varying electromotive force (EMF) across any other coils wound around the same core.

Transformer — main illustration
Transformer — illustration

Key takeaways

  • Transformer belongs to engineering; place it in that map before memorising details.
  • Learn the definition first, then one example that makes the definition concrete.
  • Connect Transformer to a quantity you can measure, compute or draw — that is where exam questions come from.
  • Reproduce the core statement of Transformer from memory before moving on to harder problems.

Reference excerpt

In electrical engineering, a transformer is a passive component that transfers electrical energy from one electrical circuit to another circuit, or multiple circuits. A varying current in any coil of the transformer produces a varying magnetic flux in the transformer's core, which induces a varying electromotive force (EMF) across any other coils wound around the same core. Electrical energy can be transferred between separate coils without a metallic (conductive) connection between the two circuits. Faraday's law of induction, discovered in 1831, describes the induced voltage effect in any coil due to a changing magnetic flux encircled by the coil. Transformers are used to change AC voltage levels, such transformers being termed step-up or step-down type to increase or decrease voltage level, respectively. Transformers can also be used to provide galvanic isolation between circuits as well as to couple stages of signal-processing circuits. 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. A wide range of transformer designs is encountered in electronic and electric power applications. Transformers range in size from RF transformers less than a cubic centimeter in volume, to units weighing hundreds of tons used to interconnect the power grid.

Principles

Ideal transformer An ideal transformer is linear, lossless, and perfectly coupled. Perfect coupling implies infinitely high core magnetic permeability and winding inductance and zero net magnetomotive force (i.e. ipnp − isns = 0).

A varying current in the transformer's primary winding creates 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 force or voltage in the secondary winding. This electromagnetic induction phenomenon is the basis of transformer action and, in accordance with Lenz's law, the secondary current so produced creates a flux equal and opposite to that produced by the primary winding. The windings are wound around a core of infinitely high magnetic permeability so that all of the magnetic flux passes through both the primary and secondary windings. With a voltage source connected to the primary winding and a load connected to the secondary winding, the transformer currents flow in the indicated directions and the core magnetomotive force cancels to zero. According to Faraday's law, since the same magnetic flux passes through both the primary and secondary windings in an ideal transformer, a voltage is induced in each winding proportional to its number of turns. The transformer winding voltage ratio is equal to the winding turns ratio. An ideal transformer is a reasonable approximation for a typical commercial transformer, with voltage ratio and winding turns ratio both being inversely proportional to the corresponding current ratio. The load impedance referred to the primary circuit is equal to the turns ratio squared times the secondary circuit load impedance.

Real transformer

Deviations from ideal transformer The ideal transformer model neglects many basic linear aspects of real transformers, including unavoidable losses and inefficiencies. (a) Core losses, collectively called magnetizing current losses, consisting of

Hysteresis losses due to nonlinear magnetic effects in the transformer core, and Eddy current losses 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 associated with:

Joule losses due to resistance in the primary and secondary windings Leakage flux that escapes from the core and passes through one winding only, resulting in primary and secondary reactive impedance. (c) similar to an inductor, parasitic capacitance and self-resonance phenomenon due to the electric field distribution. Three kinds of parasitic capacitance are usually considered and the closed-loop equations are provided

Capacitance between adjacent turns in any one layer; Capacitance between adjacent layers; Capacitance between the core and the layer(s) adjacent to the core; Inclusion of capacitance into the transformer model is complicated, and is rarely attempted; the 'real' transformer model's equivalent circuit shown below does not include parasitic capacitance. However, the capacitance effect can be measured by comparing open-circuit inductance, i.e., the inductance of a primary winding when the secondary circuit is open, to a short-circuit inductance when the secondary winding is shorted.

Leakage flux

… excerpt ends here. Continue reading the full article.

Illustrations

Transformer illustration
Transformer illustration
Transformer illustration
Transformer: Ideal transformer connected with source VP on primary and load impedance ZL on secondary, where 0 < ZL < ∞.
Ideal transformer connected with source VP on primary and load impedance ZL on secondary, where 0 < ZL < ∞.
Transformer: Ideal transformer and induction law[d]
Ideal transformer and induction law[d]

Worked examples

Example 1 — a first encounter with Transformer

Start with the simplest possible case. Write down what Transformer claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In engineering, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Transformer before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Transformer ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Transformer

In research
Transformer appears in engineering research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry
Engineering practice reuses Transformer in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom
Transformer is common in secondary-school and first-year university syllabi. It links to neighbouring topics 19th-century inventions, British inventions, Electric power conversion, so understanding it makes those chapters shorter.
In everyday life
Look for Transformer outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Transformer in 20 minutes

  1. Read the reference excerpt below once, without taking notes.
  2. Close the page and write down what Transformer means in your own words.
  3. Compare your version with the excerpt and mark what you missed.
  4. Work through the three examples above with pen and paper.
  5. Explain Transformer out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Transformer in simple terms?

In electrical engineering, a transformer is a passive component that transfers electrical energy from one electrical circuit to another circuit, or multiple circuits. A varying current in any coil of the transformer produces a varying magnetic flux in the transformer's core, which induces a varying…

Why does Transformer matter?

Because it connects several engineering ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Transformer?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Transformer.

Tags

  • 19th-century inventions
  • British inventions
  • Electric power conversion
  • Electric transformers
  • Electrical engineering
  • Hungarian inventions

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