In the efficient working of electrical circuits, Electrical Relays play an important role. They make sure that the switching of the components incorporated in a circuit is done according to the requirements. In this blog, we will look into electrical relays, their working circuits, working examples, and applications.
A relay is an electrical component that acts as a switch to control the flow of electric current between two or more circuits. It is an electromechanical device that uses an electromagnetic coil to generate a magnetic field, which activates a set of contacts to open or close the circuit. Electrical relays control high-voltage circuits with low-voltage signals, isolating the input and output circuits.
Fig 1: Electrical Relay
Components of an Electric Relay
An electrical relay consists of several key parts that work together to control the flow of electric current.
Coil: The coil is made of copper wire and is wound around a core. When an electrical current flows through the coil, it generates a magnetic field.
Core: The core, often made of iron or ferrous material, enhances the magnetic properties of the coil. It intensifies the magnetic field created by the coil when it is energized.
Armature: The relay’s contacts connect to a movable component known as the armature. It is typically a spring-loaded mechanism that responds to the magnetic field generated by the coil. When the coil is energized, the armature is attracted or repelled, causing it to move and actuate the contacts.
Contacts: The contacts are the switching elements of the relay. They can be normally open (NO), normally closed (NC), or both (changeover or double-throw). In its relaxed state (when the coil is not energized), the relay’s contacts are in their default position. Energizing the coil causes the armature to move, changing the positions of the contacts and either opening or closing the circuit.
Contacts Spring: This spring provides the necessary force to return the contacts to their default positions when the coil is de-energized. It ensures reliable switching between open and closed states.
Enclosure: Electric Relays are often enclosed in a protective housing to shield the internal components from environmental factors like dust and moisture. Sometimes it has mounting features for easy installation.
Terminals: These are the connection points where external wires or circuits are connected to the relay. They allow for the input and output connections needed to control electrical devices.
How Do Relays Work
Now we go through the step-by-step functioning of an electrical relay:
1. Resting State (No Current Flow)
- The relay is in its resting state with no electrical current flowing through the coil.
- The contacts are in their default positions based on the relay’s design (normally open, normally closed, or changeover).
2. Applying a Control Signal (Energizing the Coil):
- When a low voltage control signal is applied to the coil, an electrical current flows through it.
- The coil becomes an electromagnet, generating a magnetic field around the core.
3. Activation of Armature:
- The magnetic field produced by the energizing coil attracts the armature, which is mechanically linked to the contacts.
- The armature moves in response to the magnetic force, overcoming the tension of the contact spring.
4. Changing the Position of Contacts:
- The movement of the armature causes a change in the position of contacts.
- In a normally open relay, the contacts close, allowing current to flow through the circuit.
- In the normally closed relay, the contacts open, interrupting the current flow.
5. Establishing Current Flow:
- Depending on the relay type, the change in contact position either establishes a new electrical connection or interrupts an existing one.
- This enables the relay to control the flow of electrical current in another circuit, often with a higher voltage or current capacity.
6. Maintaining the state (As Long as the Control Signal is applied):
- The relay remains in this new state as long as the control signal is maintained.
- The armature stays attracted, and the contacts remain in their altered positions.
7. Releasing the Armature (Removing the Control Signal):
- When the control signal is removed (current stops flowing through the coil), the magnetic field collapses.
- The tension of the contact spring returns the armature to its original position.
8. Restoring Default State of Contacts:
- As the armature returns to its resting position, the contacts revert back to their default state.
- If contacts were closed, they opened, and vice versa.
9. Resetting for the Next Cycle:
- The relay is now back in its resting state and is ready for the next cycle when a control signal is applied.
Internal Circuit of Relay
Lets now discuss the internal Circuitry of a relay :
Here, we have a power source that drives the whole circuitry. Directly connected to the source is a switch that controls the current passing on to the Controlling Coil. Next the switching contacts are in connection to the power source and work in correspondence to the energizing of the Coil. When the contacts are open, the current is unable to pass on to the loads, and when they are closed, the load receives the current and starts functioning.
Fig 2: Internal Circuit of Electric Relay
Example Circuit of a Light Bulb Operation using a Relay
Now, let’s discuss the functionality of the relay using the simple working mechanism of this light bulb operation. The relay operates with a 9V battery supplying power. An on/off switch is included for the switching functionality of the relay. When the switch is open, it connects the common port to the normally open terminal of the relay. As the switch closes, the current starts to flow through the circuit, and the common port, this time, connects itself to the normally closed terminal of the relay, and in response, the bulb turns on.
Fig 3: Light Bulb Operation Using Electrical Relay
Types of Relays
Single Pole Double Throw(SPDT) Relay
One common terminal, one usually open (NO) terminal, and one normally closed (NC) terminal make up an SPDT relay. The common terminal links to either the NO or NC terminal, depending on the relay’s status.
Fig 4: SPDT Relay
Single Pole Single Throw(SPST) Relay
One ordinarily open (NO) terminal and one common terminal make up an SPST relay. It’s just an ordinary on/off switch.
Fig 5: SPST Relay
Double Pole Single Throw (DPST) Relay
Two independent single-pole switches that run concurrently make up a DPST relay. Every switch has one ordinarily open (NO) terminal and one common terminal.
Fig 6: DPST Relay
Double Pole Double Throw (DPDT) Relay
A DPDT relay offers two sets of transfer contacts in addition to two independent double-throw switches. It consists of two ordinarily open (NO), two normally closed (NC), and two common terminals (one for each pole).
Fig 7: DPDT Relay
Applications of Electrical Relays
These devices have the capacity to regulate and switch electrical circuits, therefore electrical relays are extensively employed in many different technological applications. The following are some technical applications for electrical relays:
Motor Management
Relays often control the functioning of electric motors. In appliances, conveyor systems, and industrial equipment, among other uses, they aid in the starting, stopping, and reversing of motors.
Automation in Industry
Relays are essential parts of automation systems in industrial environments. They manage the turning on and off of manufacturing lines, process equipment, and machinery.
Protection of Power Systems
In power systems, relays are essential for safeguarding against anomalies and defects. With their ability to identify abnormalities such as undercurrent, overcurrent, overvoltage, undervoltage, and others, they can pinpoint problematic areas of the electrical network and start precautionary measures.
Air Conditioning Systems
HVAC (heating, ventilation, and air conditioning) systems use relays to regulate components such as fans, compressors, and heating elements. Relays aid in controlling air circulation and temperature.
Telecommunications
Telecommunications networks use relays to regulate power distribution for equipment, route signals, and switch between multiple communication channels.
Automobile Systems
In cars, relays play a crucial role in managing functions such as power windows, wipers, headlights, and other electrical components.
Safety Measures
Security and access control systems use relays to manage devices, including door locks, alarms, and security cameras. Relays facilitate the management and integration of various security elements.
Industry Process Control
In industrial processes, relays precisely regulate variables like flow, pressure, and temperature. They make industrial process automation and optimization easier.
Conclusion
In conclusion, electrical relays are essential elements that play a crucial role in ensuring the effective operation of electrical circuits. They provide accurate manipulation and transition of components, serving as a crucial element in diverse applications such as motor regulation, industrial automation, power systems safeguarding, and other related fields. Comprehending the constituent parts and operational principles of relays elucidates their inherent adaptability. The given illustrations, descriptions of internal circuitry, and demonstration of actual light bulb functioning highlight their practical use in real-life scenarios. As technology progresses, relays remain important in ensuring the dependability and effectiveness of electrical systems in many sectors.
