7th lecture. Electromechanical elements plan

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7th lecture. Electromechanical elements


PLAN:

1. 
   Electromechanical elements
   

2. 
   Electromagnetic relays
   

2. 
   Induction relays
   

Basic words and phrases

Electromechanical elements, electromechanical relay, electromagnetic relay, induction relay, maximum relay, minimum relay, return coefficient of relay, torque of induction relay

Elements that convert electrical energy into mechanical energy or mechanical energy into electrical energy are called electromechanical elements. Electromechanical relays, which are part of electromechanical elements, are widely used in relay protection and automation.

The relay gives a signal to jump (abruptly) change the state of the controlled circuit when the value characterizing the disturbance of the controlled object'smode reaches a predetermined value. For example, it affects power devices (switches).

Electromechanical relays are divided into electromagnetic, induction and magnetoelectric relays. The main requirements for contacts and sockets of the main elements of electromechanical relays are as follows:

• 
  The contacts of the relays must be designed to reliably disconnect and connect the current in the circuits they control and to operate sufficiently many times;
  

• The coil of the relay should

have thermal stability when a permissible current passes or a permissible voltage is applied to it for a long and a short time.

Electromagnetic relays

In the electromagnetic principle, mainly three types of relays are made: pull-out anchored, pivoted anchored and transversely moved anchored.

All types of electromagnetic relays (Fig. 1.6) consist of a magnetic core 1, a coil 6, a moving armature 2, a moving contact 4, a non-moving contact 3, a resistance spring 5.

The current Ir flowing through the coil creates a magnetizing force (ms) Irÿwr , under its influence the generated magnetic flux F passes through the electromagnetic core 1, the air gap ÿ and the moving armature 2. The armature is magnetized and attracted to the electromagnetic pole. The movable contact 4 together with the armature connects the stationary contacts 3. The initial position of the anchor is bounded by the support.

The electromagnetic force pulling the armature is proportional to the square of the

2
magnetic flux F in the air gap, F = kF. Magnetic flux


^F=I r wr /Rm ,
where Ir is the current passing through the coil, wr is the number of windings, Rm is the magnetic resistance.
Machine Translated by Google

Figure 1.6. Electromagnetic relays
The electromagnetic force Fe=kw2 I 2 /R2 is proportional to the square of the current, that is, it does not depend on the direction (sign) of the current. Therefore, the electromagnetic principle is suitable for making both DC and AC relays.
Current, voltage, interval, signal and time relays operating on the electromagnetic principle are made.

The electromagnetic force Fe creates a torque Me Me =Fe Lr , where Lr is the shoulder

of the force Fe .

For the relay to work, the electromagnetic force must be greater than the resistance	mass
force of the spring Fn , and the friction force Fu , that is, Fe
=Fe.ru=Fn +Fu or Me = Me.ru =Mn +Mu .
The smallest current at which the relay operates is called the relay starting current and is		ri

denoted by I.

To change the starting current of the relay, the number of windings in the relay coil is changed Wr , the resistance of the spring is Fn , or the size of the air gap ÿ is changed to change the magnetic resistance Rm .

The operating current of the relay is smooth and winding in practice by adjusting the spring is changed step by step by changing the number.

The relay is the largest in the circuit, which returns to its initial position after being activated The current is called the return current of the relay and is defined by Irq .

The return coefficient of the relay is the ratio of the return current to the operating current and is denoted by Kq .

11. 
    q^{= I} rq^/I ri
    

Relays can be maximum or minimum. A relay that operates when the current increases is

called a maximum relay and a relay that operates when the current decreases is called a minimum relay.

The armature of the minimum relay is normally tensioned.

The minimum relay operating current is the largest armature return current, and the minimum armature current is the return current. The return coefficient of the maximum relay is Kq< 1, and the return coefficient of the minimum relay is Kq> 1.