Skip to main content

Electromechanical Relays

As the name indicates, electromechanical relays use the principle of inter conversion between electrical and mechanical energies. The most common type of electromechanical relay is the induction coil.

Basic operation of an electromechanical relay:


  1. The relay used should activate the circuit breaker when an over current occurs, thereby the circuit breaker disconnects the current flow and prevent the circuit components from damages.
  2. Usually a current transformer is used and current flows through its secondary only when over current flows.
  3. The current across the secondary of the transformer energizes the relay coil which in turn breaks the circuit connection in the circuit breaker.
  4. Thus further damages are prevented.


In the case of induction relays, there may be one or more exciting coils wound around a magnetic core. Due to flow of current in the exciting coil, the electromagnetic torque is produced which rotates the rotor.

This rotation of rotor is translated into mechanical action for closing of relay.

Types of induction relay:

  1. Induction disk relays
  2. Induction cup relays
  3. Hinged armature relays


Disadvantages of Electromechanical relays
Electromechanical relays are widely used for various applications but they suffer the following drawbacks:

  1. High burden on instrument transformers
  2. High operating time due to high inertia
  3. Contact pitting and corrosion
  4. Contact Racing: The Phenomenon by which the inertia of the moving parts causes unwanted connections in the circuit, which makes relay co-ordination difficult.
  5. Requires frequent maintenance as there are several moving parts.
  6. It is easily affected by shocks and vibrations from outside
Labels:

Comments

Post a Comment

Comment Policy
We’re eager to see your comment. However, Please Keep in mind that all comments are moderated manually by our human reviewers according to our comment policy, and all the links are nofollow. Using Keywords in the name field area is forbidden. Let’s enjoy a personal and evocative conversation.

Popular posts from this blog

Demagnetising and Cross Magnetizing Conductors

The conductors which are responsible for producing demagnetizing and distortion effects are shown in the Fig.1. Fig. 1        The brushes are lying along the new position of MNA which is at angle θ  from GNA. The conductors in the region AOC = BOD = 2θ  at the top and bottom of the armature are carrying current in such a direction as to send the flux in armature from right to left. Thus these conductors are in direct opposition to main field and called demagnetizing armature conductors.         The remaining armature conductors which are lying in the region AOD and BOC carry current in such a direction as to send the flux pointing vertically downwards i.e. at right angles to the main field flux. Hence these conductors are called cross magnetizing armature conductors which will cause distortion in main field flux.        These conductors are shown in the Fig. 2 Fig. 2  ...
Post a Comment
Read more

Armature Voltage Control Method or Rheostatic Control of dc motor

Speed Control of D.C. Shunt Motor (Part2)  2. Armature Voltage Control Method or Rheostatic Control        The speed is directly proportional to the voltage applied across the armature. As the supply voltage is normally constant, the voltage across the armature can be controlled by adding a variable resistance in series with the armature as shown in the Fig. 1. Fig. 1 Rheostat control of shunt motor        The field winding is excited by the normal voltage hence I sh is rated and constant in this method. Initially the reheostat position is minimum and rated voltage gets applied across the armature. So speed is also rated. For a given load, armature current is fixed. So when extra resistance is added in the armature circuit, I a remains same and there is voltage drop across the resistance added ( I a R). Hence voltage across the armature decreases, decreasing the speed below normal value. By varyi...
Post a Comment
Read more

Characteristics of Separately Excited D.C. Generators

The characteristics is separately excited d.c. generator are divided into two types, 1) Magnetization   and         2) Load characteristics. 1.1 Magnetization or Open Circuit Characteristics         The arrangement to obtain this characteristics is shown in the Fig. 1. Fig. 1  Obtaining O.C.C. of separately excited generator        The rheostat as a potential driver is used to control the field current and the flux. It is varied from zero and is measured on ammeter connected.        E o  = (ΦPNZ) / (60A)        As I f is varied, then Φ change and hence induced e.m.f. E o  also varies. It is measured on voltmeter connected across armature. No Load is connected to machine, hence characteristics are also called no load characteristics which is graph of E o  against field current I f as sho...
Post a Comment
Read more