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Relais with shading coil (arrow head) for operating with AC

A shading coil or Shading ring (Also called Frager spire or Frager coil) is a single turn of electrical conductor (usually copper or aluminum) palced in the face of the magnet assembly or armature. The main alternating magnetic flux induces currents in the Frager coil. So, these induced currents create auxiliary magnetic flux out of phase from the main flux[1]. In other words, shading coil's purpose is to give sizeable phase-shifted magnetic field to keep the contactor on when the main coil flux passes through zero, avoiding unwanted chatter[2] and mechanical destruction of the magnet and power contacts.

The property of property allows the armature sealed-in when the main flux falls to zero (e. 100 (or 120) times / second with 50 (or 60) cycles AC).

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 (e.g. reducing the bouncing of relay or power contacts and the chatter)[3]

Shaded-pole motors

Shaded-pole motors are provided with a main winding connected to the single-phase electric supply. In addition, that kind of AC motors have a permanently short-circuited winding, known as a shading coil and located ahead of the main winding in the direction of rotation. This shading coil consists of one (e.g. shading ring) or more (z.g. shading coil) shorted turns. The shading coil allows to delay the establishment of magnetic flux in the region that it encircles and producing thereby a small component of rotating field at standstill[4].

References

  1. ^ https://www.researchgate.net/figure/Sketch-of-the-contactors-electromagnet-dimensions-in-centimeter-Not-to-scale_fig2_259577477
  2. ^ https://www.chegg.com/homework-help/explain-shading-coil-ac-contactor-reduces-chatter-chapter-13-problem-2rq-solution-9780130612106-exc
  3. ^ https://cr4.globalspec.com/thread/56783/Shading-Ring
  4. ^ https://www.britannica.com/technology/electric-motor/Capacitor-induction-motor#ref152155
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