Sites: GlobalSpec.com | GlobalSpec Electronics | CR4 | Electronics360
Login | Register
The Engineer's Place for News and Discussion®

Previous in Forum: Maximum Runs On A Busbar According To Standards   Next in Forum: Maximum Power Carrying Capacity
Close

Comments Format:






Close

Subscribe to Discussion:

CR4 allows you to "subscribe" to a discussion
so that you can be notified of new comments to
the discussion via email.

Close

Rating Vote:







7 comments
Member

Join Date: Jul 2010
Posts: 5

Shading Ring

07/05/2010 6:55 AM

Sir,

I want to know about the shading ring provided in the core of a contractor. What is the function of that shading ring?

Register to Reply
Pathfinder Tags: CONTACTOR CORE SHADDING RING
Interested in this topic? By joining CR4 you can "subscribe" to
this discussion and receive notification when new comments are added.

Comments rated to be Good Answers:

These comments received enough positive ratings to make them "good answers".
Commentator

Join Date: May 2008
Posts: 96
#1

Re: ELECTRICAL ENG.

07/05/2010 7:17 AM

Hi NARAYAN SHARMA

See have a look at this thread:

http://cr4.globalspec.com/thread/30566/humming-contactor-250v-ac

Thanks...............

__________________
look for "learning & knowledge" even in Antarctica
Register to Reply
2
Guru
India - Member - New Member

Join Date: Sep 2009
Location: Bangalore, India
Posts: 2644
Good Answers: 154
#2

Re: ELECTRICAL ENG.

07/05/2010 8:05 AM

A shading coil is a single turn of conducting material (generally copper or aluminum) mounted in the face of the magnet assembly or armature. The alternating main magnetic flux induces currents in the shading coil and these currents set up auxiliary magnetic flux which is out of phase from the main flux. The auxiliary flux produces a magnetic pull out of phase from the pull due to the main flux and this keeps the armature sealed-in when the main flux falls to zero (which occurs 100 times per second with 50 cycles ac). Without the shading coil, the armature would tend to open each time the main flux goes through zero. Excessive noise, wear on the magnet faces, and heat would result.

You will require more knowledge of contactorsm relays and starters. Please visit this link and download the pdf file which is very informative : Motor control

__________________
Nothing worthwhile can ever be taught, it can only be learnt.
Register to Reply Good Answer (Score 2)
Power-User

Join Date: Nov 2008
Location: India
Posts: 333
Good Answers: 6
#3

Re: ELECTRICAL ENG.

07/05/2010 12:15 PM

dear sir,

This shadding ring produces the magnetic field, that reduces the bouncing of contacts during starting, reducing the wear & tear of the power contacts. Also, it helps in reducing the chattering / humming of the contactors.

__________________
Exploring the Science of Electricity
Register to Reply
2
Guru
India - Member - New Member

Join Date: Sep 2009
Location: Bangalore, India
Posts: 2644
Good Answers: 154
#4
In reply to #3

Re: ELECTRICAL ENG.

07/05/2010 9:21 PM

Partially correct i am afraid.

Shading coil's purpose is to give enough phase-shifted magnetic field to keep the contactor on when the main coil flux passes through zero, thereby avoiding chatter and mechanical destruction of the magnet, and the power contacts also. Here is an image of the main and shaded flux forces.

The shading coil does not help in reduction of contact bounce. Bounce reduction is achieved by different means by many designers...elastomer buffers on magnets, leaf springs on contacts and armatures, bell-crank design like this one ...

More recently, designers have resorted to using electronically controlled coils for contactors, some of which give just enough force to the magnet to close and seal, thereby practically eliminating bounce. Here is an image from a patent, which shows the tailored force curve.

__________________
Nothing worthwhile can ever be taught, it can only be learnt.
Register to Reply Good Answer (Score 2)
Guru

Join Date: Feb 2006
Posts: 1775
Good Answers: 6
#5
In reply to #4

Re: ELECTRICAL ENG.

07/06/2010 8:22 AM

GA for excellently description.

I like to add from:

Shaded-pole_motor

A shaded-pole motor is a type of AC single-phase induction motor. It is basically a small squirrel cage motor in which the auxiliary winding is composed of a copper ring surrounding a portion of each pole.[1] This auxiliary winding is called a shading coil. Currents in this coil delay the phase of magnetic flux in that part of the pole enough to provide a rotating magnetic field. The direction of rotation is from the unshaded side to the shaded (ring) side of the pole.[2] The effect produces only a low starting torque compared to other classes of single-phase motors.

Register to Reply
Guru
India - Member - New Member

Join Date: Sep 2009
Location: Bangalore, India
Posts: 2644
Good Answers: 154
#6
In reply to #5

Re: ELECTRICAL ENG.

07/06/2010 9:26 AM

Thanks. In fact, i believe the shaded pole motor came first!

__________________
Nothing worthwhile can ever be taught, it can only be learnt.
Register to Reply
Guru

Join Date: Feb 2006
Posts: 1775
Good Answers: 6
#7
In reply to #6

Re: ELECTRICAL ENG.

07/06/2010 7:54 PM

Regards.

May be!

When I started job in 1950s in late 50s a clock driven by Shaded pole motor was in there but got involved in Power Electricity & Electronics quite late 70s where I came accross Shaded Pole AC relays & in late 80s Contactors.

Register to Reply
Register to Reply 7 comments
Interested in this topic? By joining CR4 you can "subscribe" to
this discussion and receive notification when new comments are added.

Comments rated to be Good Answers:

These comments received enough positive ratings to make them "good answers".
Copy to Clipboard

Users who posted comments:

Ali18 (1); Haajee (2); harry potter (1); kvsridhar (3)

Previous in Forum: Maximum Runs On A Busbar According To Standards   Next in Forum: Maximum Power Carrying Capacity
You might be interested in: Metal Ring Seals, V-ring Seals, Ring Gages