IDMT Relays

You also asked in another thread if a relay can work with AC.

What school do you attend?

yaa...actually i had a doubt wagging behind my mind if relay operates in D.C as well?

How do you think a simple relay and/or switch works?

Well! as far as my knowledge is concerned, a relay is a electromechanical switch....thats how it differs from a simple switch.

And also a simple switch can be manipulated by humans but a Relay operation is not human manipulated..isn't it?

Hmm, this may become more painful than I originally imagined. Particularly since you started this thread asking about a very sophisticated relay and you posted another thread about a basic relay characteristic. You're making me wonder if you're playing me.

An electromagnet can attract and therefore move ferromagnetic material. A switch completes or interrupts a circuit by moving something. A relay is an electromagnetically controlled switch.

Looking at your threads and responses, I cannot help but wonder... What have you done with the money you were supposed to spend on textbooks? Surely some of the information you seek is between the covers of some of them.

The question is "What is the mechanism involved in bridging the two fixed contacts by the moving contact?"

Answer-

Induction relays, are available in many variations to provide accurate pickup and time-current responses for a wide range of simple or complex system conditions. They're actually like induction motors. On the relay, the moving element (rotor) is usually a metal disk, although sometimes it's a metal cylinder or cup. The stationary part (stator) is one or more integral electromagnets, with current or potential coils inducing currents in the disk, causing it to rotate. Until the rotational forces are great enough to turn the disk and bring its moving contact against the stationary contact, a spring restrains the disk motion. This closes the circuit the relay is controlling. The greater the sensed fault, the greater the current in the coils, and the faster the disk rotates.

A calibrated adjustment called the time dial sets the spacing between the moving and stationary contacts; this varies the operating time of the relay from fast (contacts only slightly open) to slow (contacts nearly a full disk revolution apart). Reset action begins upon removing the rotational force, either by closing the relay contact that trips a breaker or by otherwise removing the malfunction the relay is sensing. The restraining spring resets the disk to its original position. The time required to reset depends on the type of relay and the time-dial setting (contact spacing).

With multiple magnetic coils, these relays can sense several conditions of voltage and current simultaneously. The coils' signals can be additive or subtractive in actuating the disk. For example, a current-differential relay has two current coils with opposing action. If the two currents are equal, regardless of magnitude, the disk does not move. If the difference between the two currents exceeds the pickup setting, the disk rotates slowly for a small difference and faster for a greater difference. The relay contacts close when the difference continues for the length of time determined by the relay characteristics and settings. By using multiple coils, directional relays can sense the direction of current or power flow, as well as magnitude. Since induced magnetic fields from AC magnets create the disk's movement, induction relays are almost completely unresponsive to the DC component of an asymmetrical fault.

From EC&M

You know by having other people do your work your not learning. Now if you are wanting to verified your understanding of something. Ask it as such. You will attract a lot more answers being humble that attacking the people that your asking help from.

Since you have access to a computer. Learn how to filter the search terms your trying to get info about. You may learn more, also you may spot when someone gives you miss-information about something. Or it may broaden your knowledge enough to ask additional questions.

Charles