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Shading coil

Shading coil is a physics 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 Shading coil rather than just read about it. In short: A shading coil or shading ring (Also called Frager spire or Frager coil) is one or more turns of electrical conductor (usually copper or aluminum) located in the face of the magnet assembly or armature of an alternating current solenoid, and only encircles part of the magnetic path. The alternating current in the energized primary coil induces an alternating current in the shading coil.

Shading coil — main illustration
Shading coil — illustration

Key takeaways

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

Reference excerpt

A shading coil or shading ring (Also called Frager spire or Frager coil) is one or more turns of electrical conductor (usually copper or aluminum) located in the face of the magnet assembly or armature of an alternating current solenoid, and only encircles part of the magnetic path. The alternating current in the energized primary coil induces an alternating current in the shading coil. This induced current creates an auxiliary magnetic flux which is 90 degrees out of phase from the magnetic flux created by the primary coil.

Because of the 90 degree phase difference between the current in the shading coil and the current in the primary coil, the shading coil maintains a magnetic flux and hence a force between the armature and the assembly while the current in the primary coil crosses zero. Without this shading ring, the armature would tend to open each time the main flux goes through zero and create noise, heat and mechanical damages on the magnet faces, so it reduces bouncing or chatter of relay or power contacts.

Shaded-pole AC motors

A shaded-pole motor is an AC single phase induction motor. Its includes an auxiliary winding composed of a copper ring called a shading ring (or shading coil with more than one turn). The auxiliary winding produces a secondary magnetic flux which, along with the flux from the primary coil, forms a rotating magnetic field suitable for applying torque to and rotating the rotor. These devices are typically used as low-cost motors for microwave oven fans.

References

External links

The short film AC MOTORS AND GENERATORS (1961) is available for free viewing and download at the Internet Archive. The short film AC MOTORS (1969) is available for free viewing and download at the Internet Archive. Engineer's Relay Handbook, 5th edition, published by the Relay and Switch Industry Association (RSIA) – formerly NARM Information about relays and the Latching Relay circuit "Harry Porter's Relay Computer", a computer made out of relays "Relay Computer Two", by Jon Stanley

Illustrations

Shading coil: AC relay with shading coil (red arrow near top) for operating with AC
AC relay with shading coil (red arrow near top) for operating with AC
Shading coil: Frager spire or shading coil's purpose is to provide sizeable phase-shifted magnetic field (in blue) to keep the contactor on when the main coil flux (in red) passes through zero, avoiding unwanted chatter[2] and mechanical destruction of the magnet and power contacts. .
Frager spire or shading coil's purpose is to provide sizeable phase-shifted magnetic field (in blue) to keep the contactor on when the main coil flux (in red) passes through zero, avoiding unwanted chatter[2] and mechanical destruction of the magnet and power contacts. .
Shading coil: Operation of a two-pole squirrel-cage shaded-pole motor showing its rotating magnetic field
Operation of a two-pole squirrel-cage shaded-pole motor showing its rotating magnetic field

Worked examples

Example 1 — a first encounter with Shading coil

Start with the simplest possible case. Write down what Shading coil claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In physics, 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 Shading coil 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 Shading coil 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 Shading coil

In research
Shading coil appears in physics 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 Shading coil 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
Shading coil is common in secondary-school and first-year university syllabi. It links to neighbouring topics AC motors, Electromagnetic components, Power engineering, so understanding it makes those chapters shorter.
In everyday life
Look for Shading coil 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 Shading coil in 20 minutes

  1. Read the reference excerpt below once, without taking notes.
  2. Close the page and write down what Shading coil 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 Shading coil out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Shading coil in simple terms?

A shading coil or shading ring (Also called Frager spire or Frager coil) is one or more turns of electrical conductor (usually copper or aluminum) located in the face of the magnet assembly or armature of an alternating current solenoid, and only encircles part of the magnetic path. The alternating…

Why does Shading coil matter?

Because it connects several physics 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 Shading coil?

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 Shading coil.

Tags

  • AC motors
  • Electromagnetic components
  • Power engineering
  • Relays

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