In this note, we are going to learn about some Types of Relays in Electrical Power Systems that are used. Welcome to Poly Notes Hub, a leading destination for engineering notes.
Author Name: Arun Paul.
Types of Relays in Electrical Power Systems
Here we have listed different types of protection relays in the electrical system, or electrical substations. If you are searching different types of protection relays in web then you are in the right place. Here in this note, we will learn about many types of relays or protection relays that are used in the electrical power system.
1. Electromagnetic Relay
An electromagnetic relay is an electrically operated switch that uses the magnetic field generated by an electromagnet. When current passes through a coil within the relay, it creates a magnetic field that pulls a movable armature. This movement establishes or breaks an electrical contact, hence managing a bigger current or circuit. These relays, which operate on the concept of electromagnetic induction, are frequently used for switching and protection in control systems.
Applications of Electromagnetic Relay
- Used for overload and short-circuit protection in electrical circuits
- Applied in industrial automation control panels
- Used in motor starting and control circuits
- Implemented in alarm and signaling systems
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2. Directional Relay
A directional relay detects the direction in which power or fault current flows in a system. It calculates the phase angle and direction using voltage and current inputs. The relay will only trip if the current flows in a certain, predetermined direction, making it perfect for selective protection in complex systems. It normally consists of a directing unit (polarizing circuit) and a tripping unit.
Applications of Directional Relay
- Used for the protection of feeders in interconnected power systems
- It is applied in ring main and loop networks
- Used in parallel feeders and transformer protection
- It is provides selectivity in grid-connected systems
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3. Microprocessor Relay
A microprocessor relay is a digital protection device that analyzes input signals and makes programmed choices. Analog inputs (voltage/current) are transformed into digital signals, which are then evaluated by algorithms to detect defects and generate trip signals. These relays provide multifunctional capabilities such as overcurrent, undervoltage, frequency protection, and communication via standards such as IEC 61850.
Applications of Microprocessor Relay
- Widely used in modern power substations
- Ideal for transformer and generator protection
- Used in SCADA and remote monitoring systems
- Employed in industrial motor protection systems
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4. Static Relay
A static relay is a sort of protective relay in which solid-state electronic components (such as transistors, diodes, and logic gates) perform switching functions instead of moving mechanical parts. It accepts input from Current Transformers and Potential Transformers, processes it through amplifiers and comparators, and if the requirements are met, delivers the output to the trip coil. Because there are no moving parts, it responds quickly, accurately, and reliably.
Application of Static Relay
- Protection in high-voltage transmission systems
- Used in fast tripping circuits for motors and transformers
- Applied in switchgear and control panels
- Ideal for remote and unmanned substations
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5. Solid State Relay
A solid-state relay (SSR) is an electronic switching device that uses semiconductor components such as thyristors or triacs to switch on and off without physical touch. When a tiny control voltage is provided to the input side (LED or optoisolator), the output semiconductor conducts, completing the load circuit. SSRs provide fast operation, silent switching, and electrical isolation between control and output.
Applications of Solid State Relay
- Used in HVAC and industrial heating systems
- Suitable for automation and robotic controls
- Ideal for switching AC or DC loads in electronics
- Employed in precise temperature control circuits
6. Relay Module
A relay module is a small circuit board that contains one or more relays as well as the appropriate driving electronics, such as transistors, diodes, and connections, to operate high-voltage devices via low-voltage signals from microcontrollers. When the microcontroller transmits a digital signal, the driver circuit energizes the relay coil, which triggers the switch that controls the linked load. It streamlines the interface between logic-level devices and high-power equipment.
Applications of Relay Module
- Commonly used in DIY and IoT projects
- Compatible with Arduino, Raspberry Pi, and other microcontrollers
- Used in home automation (lights, fans, appliances)
- Controls industrial machinery and relays remotely