What is Relay?

A relay is an electrically operated switch in the context of electronics and electrical engineering. It is made up of a coil and one or more contact sets. When an electrical current runs through the coil, a magnetic field is created that activates the contacts, allowing them to open or close the circuits. Relays are frequently employed in automotive applications, industrial automation, and control systems to control high-power or high-voltage devices with a lower-power signal.

What Is A Relay?

A simple electromagnetic switch is a relay that can be used to make or break an electrical connection. Basically, the relay is just like a mechanical switch, but we can control it with an electromagnetic signal instead of manually turning it on or off. It can be of different types, like electromechanical, which is frequently used, or solid-state. Every electromechanical relay consists of an Electromagnet, Switching points, Mechanically moveable contacts, and a spring. Also, the electromagnet is constructed by wounding a copper coil on a metal core. The two ends of the coil are connected by two pins of the relay. Two more contacts are present, called switching points to connect high ampere loads and common contacts to connect the switching points. Contacts are known as NO (Normal Open), NC (Normal Closed), and COM (Common) contacts. Someone can use a relay either in an AC circuit or a DC circuit.

Construction of Relay

Given Below is the Construction diagram of Relay

• In controlling circuits, relays involve several parts working in together. The electromagnet is an iron piece that is movable and only attracted when the coil becomes magnetized because of the current flow through it is connected to an armature that is a coil of wire and a spring which returns it to its original position.
• Relay is a metal part which depends on the position of the armature to open or close the circuit.There are two types of relay Normally open (no) and Normally Closed (Nc).The Yoke is used to give the magnetic flux produced by the electromagnet a low resistance path.

How Relay Works?

Given below is the Diagram for the relay

Diagram

Relay works on the basis of the principle of electromagnetic induction.

• Include a magnetic field around the relay, when the electromagnet is applied with some current.
• Can use a switch to apply DC current to the load.
• The copper coil and the iron core act as the electromagnet in the relay.
• Energizing of relay: When the coil is applied with DC current, it starts attracting the contact.
• De-energizing of relay: When the supply is removed it retrieves back to the original position.

DIAGRAM

Relay Contact Types

As Relay is a switch, so the terminology of 'Poles & Throws' is also applicable for relay. Relays are classified depending on the poles and throws

• Single Pole Single Throw Relay (SPST): It consists of only one pole one throw which path is easier of closed or opened. The best example for this is a Push Button. It is used for the applications which is require the ON or OFF state.
  
• Single Pole Double Throw Relay (SPDT): It consists of only one pole but has two throws. The example for this is a Slide switch. It is also called as changeover relay.
  
• Double Pole Single Throw Relay (DPST): It consists two poles and a throw. It can be used to connect two terminals of a single circuit at a time. Toggle Switch works on this property.
  
• Double Pole Double Throw Relay (DPDT): It consists two poles but the individual pole has two throws. These are used for phase or polarity reversal in motor direction control.

DIAGRAM

Types of Relays

Depending on functionality, structure and application, relays can be classified into different types:

• Electromagnetic: Uses an electromagnet to mechanically operate a switch.
• Electronic: Relies on solid-state components to switch circuits without moving parts.
• Latching or Non-Latching: Latching will be in same state after activation and non-latching returns to its default state when the activating signal is removed.
• Reed type: Consists of reed contacts in a sealed glass tube
• High Voltage: Designed to handle high voltage applications.
• Small signal :Ideal for low voltage and low current applications
• Time delay & Multi Dimensional: Delays switching action for a specified period.
• Thermal: Operates based on temperature changes.
• Differential: Compares two signals or conditions and activates when there's a difference.
• Distance: Measures distance or displacement and switches based on proximity.
• Frequency & Automotive: Designed for specific frequency ranges.
• Polarized: Has a specific polarity for operation.
• Moving coil: Uses a coil moving within a magnetic field.
• Safety & Super vision: Ensures safe operation and monitors systems for faults
• Ground fault: Detects ground faults and interrupts the circuit
• Rotary: Uses rotational movement.

Applications of Relay

There are limitless applications of relay, its main function is to control the high voltage circuit (230V AC circuit) with the low voltage(DC voltage) power supply.

• Relays are used in computer circuits in order to perform the mathematical and arithmetic operations in it.
• It used to control the electric motor switches. We need 230V AC supply to turn on an electric motor but in some cases, there can make situation to switch ON the motor with the DC supply voltage, a relay can be used for those cases.
• A Relay is used on Automatic Stabilizers. The set of relays sense the voltage variations and also controls the load circuit with the help of circuit breakers, when the supply voltage is other than rated voltage.
• If there exists more than one circuit in a system, it is used for circuit selection also.
• It is used in Traffic signal controllers, temperature controllers and televisions.

How to Test a Relay?

Some techniques to test if the Relay is working are

DIAGRAM

• With a multimeter
• By build a simple circuit
• By use a DC power supply to see the proper functioning.

Steps to Test a Relay

Given below are the Steps to Test a Relay

1. Identify Relay Terminals

• Coil Terminals which are marked or can be found on the relay data sheet.
• Common (COM) these terminals change between NO and NC Contacts
• Normally open (NO) these terminals are open when the relay is de-energized.
• Normally Closed(NC) these terminals are closed when the relay is de-energized.

2. Test the Coil

• Set the multimeter to the Resistance Mode
• Measure the coil Resistance

3. Test the Contacts (Without Power)

• Set the multimeter to the Resistance Mode
• Measure the NC Contact
• Measure the NO Contact

4. Activate the Relay

• Apply the rated voltage to the coil.

5. Test the Contacts (With Power)

• Measure the NC Contact
• Measure the NO Contact

Advantages and Disadvantages of Relay

There are some Advantages and Disadvantages of Relay given below :

Advantages of Relay

• Relay allows us to control a remote device.
• At High temperature, it works well.
• Relay can activate large machines of great power and also can active with low current.
• Relay can switch Direct Current (DC) or Alternating Current (AC).

Disadvantages of Relay

• When relay use continuous, the contacts are damage.
• At the time of activation and deactivation, it generates a lot of noise.
• It has high switching time.

Conclusion

As per the discussion of the Working Principle & Types of Relay, we understand the principle of electromagnetic attraction when it gets energized of the operating to the given signal. Basically, the required signal is given by the micro-controllers or microprocessors as well. It also used in power system operations to prevent & detent the fault.