Relay Circuit Diagram Symbol

A fan can be used in switching and protection applications to switch circuits so that the current passing through it can be transferred from the current circuit to another circuit. The switching operation can be done manually or automatically. Manual operations for switching relays are performed via buttons and other conventional switches. But in most cases, the control circuit output drives the relay automatically.

Fan appliances are used to ensure the smooth operation of any power system so that they isolate specific circuits or sound an alarm when parameters such as voltage or current exceed their limits. Therefore, the main function of relays is to turn on or off circuits in switching and protection applications, and various types of relays can be found in a variety of applications.

Composition OF Relay

A relay is an electromechanical device with electrical, magnetic, and mechanical components that controls a circuit by opening or closing its contacts. Electromechanical relays consist of three terminals, common (COM), normally closed (NC), and normally open (NO) contacts, which can be opened or closed while the relay is in operation and operate on both AC and DC power supplies.

Of course, the structure of AC and DC relays is somewhat different, but both work according to the principle of electromagnetic induction. In the case of AC relays, for each current zero position, the relay coil is demagnetized, which makes it possible to continue disconnecting the circuit. Therefore, AC relays are constructed with special mechanisms to provide sustained magnetism, thus avoiding this problem. This structure includes an electronic circuit assembly or a shield coil construction,

Most current electromechanical relays are either attractive or inductive,

Suction electromagnetic relays operate on AC and DC where the armature is attracted to the electromagnet or the armature is drawn into the solenoid through the plunger. All of these relays work on the principle of electromagnetic attraction. The electromagnetic force applied to the armature or plunger is proportional to the square of the current in the air gap or the square of the magnetic flux. These are divided into several types, such as articulated armature type, plunger type, balance beam type, moving coil type and reed type relays.

Inductive relays work according to the principle of electromagnetic induction. These types of relays are used for AC power only. In these relays, the driving force is generated by a moving contact, which can be a disk or cup shape, through the interaction of two alternating magnetic fluxes on the magnetic element. Induction relays are divided into pole type, induction cup type and energy meter relay.

Working Process Schematic Diagram

The following diagram illustrates the working process of the relay. For ease of understanding, the suction electromagnetic relay is given here. In any type of electromechanical relay, the main components are the coil, armature and contacts. A wire is wound around the core, so it forms an electromagnet. When power is supplied to this coil, it becomes energized and generates an electromagnetic field. The armature is a movable part whose main function is to open or close the contact. It has a spring attached so that under normal operating conditions, the armature returns to its original position. A contact is a conductive part that connects the load to the source circuit.

Relay Condition When Powered On

If the coil is powered by a power supply, the relay's wire is energized and produces a magnetic flux proportional to the current flowing through it. This magnetic field draws the armature towards the electromagnet, so that the moving and fixed contacts are close to each other, as shown in the figure below. For NO, NC, and COM terminals (not shown in the figure), when the relay is powered on, both the NO and COM terminals touch, while the NC contacts remain floating.

Relay Condition In Power Off State

When no power is supplied to the relay coil, no magnetic flux is generated, so the armature is at rest. Therefore, both contacts remain unchanged, and there is a small air gap between these contacts. In other words, the NC and COM contacts touch each other when the coil is powered off.

What Are The Types OF Relays

Relays can be divided into different types according to their function, structure, application, etc.

Drive relay

As mentioned above, relays allow switching high power circuits with low power circuits. Therefore, for the relay to work, the coil must be energized by running a current through the wire. Therefore, the drive circuit is necessary, and there is nothing but the control circuit of the relay. A relay drives a circuit to operate or drive a relay to properly perform a switching function in a particular circuit. The drive circuit of the drive relay mainly has two kinds: AC relay drive circuit and DC relay drive circuit.

Relay Application

Relays are used to protect electrical systems and minimize damage to connected devices in the system due to overcurrent/voltage. Relays are used to protect the equipment connected to them. These are high-voltage circuits used to control low-voltage signals in application audio amplifiers and certain types of modems. These are used to control high-current circuits through low-current signals, such as the starting solenoid of a car. It can also detect and isolate faults occurring in transmission and distribution systems. Typical application areas of relays include:

Lighting control system

Telecommunication system

Industrial process controller

Traffic control

Motor drive control

Power system protection system

Computer interface

CARS

Household appliance

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