What is Static Relay? – Block Diagram, Working | New Topic [2024]

In this note, we are going to learn about a topic called “What is Static Relay?“, and also learn about its Block Diagram, Working Principle, Advantages, and Applications as well. Welcome to Poly Notes Hub, a one-stop solution for polytechnic notes for diploma engineering students.

Author Name: Arun Paul.

What is Static Relay?

A Static Relay is a type of relay that does not have any moving elements and instead relies on solid-state electrical components such as transistors, diodes, and integrated circuits. Unlike classic electromechanical relays, which switch contacts mechanically, static relays detect defects, control signals, and make choices using electrical circuits.

Block Diagram of Static Relay

Below we listed some main sections on the static relay block diagram –

• Rectifier: The rectifier is the first component in a static relay circuit. Its principal function is to convert incoming alternating current (AC) signals to direct current (DC). This direct current (DC) signal powers the relay’s subsequent circuits.
• Relay Measuring Circuit: This circuit measures the electrical properties of the system under monitoring, such as voltage, current, frequency, and phase angle. It often uses sensors or transducers to transform physical quantities into electrical signals that the relay can process.
• Amplifier: The amplifier circuit boosts the signals received from the measuring circuit to a level that allows for additional processing. It may have operational amplifiers or other amplification circuits that boost signal power while maintaining accuracy and fidelity.
• DC Supply: Power for the relay’s output devices, logic circuits, amplifier, and other parts comes from the DC supply. It is produced by rectifying the AC signal, and it is usually regulated to guarantee the relay operates steadily.
• Output Device: The part that takes the necessary action in response to the fault conditions that are detected is the output device. This could be a thyristor, solid-state switch, or other semiconductor device that can regulate the electrical system’s current flow.
• Trip Circuit: The trip circuit is the relay’s final stage, activating the output device when a malfunction or anomaly is detected. It evaluates the amplified signals from the measuring circuit, compares them to specified threshold values or relay settings, and then instructs the output device to disconnect or isolate the problematic component of the system.

Working Principle of Static Relay

A Static Relay works by continually measuring several electrical properties such as voltage, current, frequency, and phase angle using sensors or transducers. These measured signals are processed electronically, including amplification and filtering, to ensure precision and reliability in detecting irregularities. Once processed, the signals are compared to predefined threshold levels or relay configurations. If the observed parameters exceed certain limits, indicating a defect or an abnormal situation, the relay takes preventative action.

These measures usually include regulating output devices like solid-state switches or thyristors to trip or isolate the problematic component of the electrical system. Following fault isolation, the relay may also generate signals or indicators for additional investigation and troubleshooting. Static relays serve an important role in protecting electrical equipment and systems, assuring their safety and reliability in a variety of applications ranging from power system protection to industrial automation.

Advantages of Static Relay

Below we listed some merits of this relay –

1. These relays consume less power.
2. It has less reset time.
3. These relays does not have any thermal storage problem.
4. Their sensitivity is increased by the relay’s amplified input signal.
5. Because static relays have a high shock tolerance, they can function with safety in earthquake-prone places.

Applications of Static Relay

Below we listed some important use cases of Static Relay –

1. Preventing faults in distribution networks, generators, transmission lines, and transformers.
2. To avoid damage and downtime, motor parameters are monitored and irregularities are detected.
3. Identifying inherent flaws, overvoltage, and overcurrent in transformers to stop disastrous breakdowns.