Describe working of protective relays and circuit breaker with neat circuit diagram.

Protective relays and circuit breakers work together to detect and isolate faults in electrical systems, ensuring safety and preventing damage to equipment. Here's a description of their working principles along with a simple circuit diagram:

Working of Protective Relays:

1. Sensing: Protective relays continuously monitor electrical parameters such as current, voltage, frequency, and phase angle in the system. When abnormal conditions such as overcurrent, overvoltage, or underfrequency are detected, the relay initiates a trip signal.

2. Decision Making: The relay evaluates the sensed parameters against predetermined settings or thresholds. If the measured values exceed the set limits, indicating a fault condition, the relay activates its output circuit to initiate the tripping sequence.

3. Tripping: Upon receiving the trip signal, the relay sends a signal to the circuit breaker to open its contacts and disconnect the faulty section of the electrical system from the rest of the network. This action isolates the fault, preventing further damage and ensuring the safety of personnel and equipment.

Working of Circuit Breaker:

1. Normal Operation: In normal operation, the circuit breaker's contacts remain closed, allowing current to flow through the circuit uninterrupted. The trip coil of the circuit breaker is energized but remains in a reset state.

2. Fault Detection: When a fault is detected by the protective relay, a trip signal is sent to the circuit breaker. The trip signal energizes the trip coil of the circuit breaker, generating a magnetic field that attracts the armature.

3. Opening of Contacts: The attraction of the trip coil's armature causes the circuit breaker's contacts to rapidly separate, creating an air gap and interrupting the flow of current through the circuit. This action de-energizes the faulted section of the system, isolating it from the rest of the network.

4. Arc Extinction: As the contacts open, an arc may form between them due to the electrical discharge. The circuit breaker's design includes mechanisms such as arc chutes or extinguishing chambers to extinguish the arc quickly and safely.

5. Reset and Reclosing: After the fault is cleared, the circuit breaker can be manually or automatically reset to its closed position. Some circuit breakers also incorporate automatic reclosing features to attempt re-energizing the circuit after a brief delay, provided the fault condition has been cleared.

Circuit Diagram:

            Protective Relay
               |
               | Trip Signal
               v
             Circuit Breaker
               |
               | Contacts
               v
          Faulted Section

In the circuit diagram, the protective relay senses the fault condition and sends a trip signal to the circuit breaker, causing it to open its contacts and isolate the faulted section of the electrical system. This diagram represents the basic interaction between protective relays and circuit breakers in a typical electrical installation.