Protective Relay in Electrical Power Systems

𝗥𝗲𝗹𝗮𝘆 𝗖𝗼𝗼𝗿𝗱𝗶𝗻𝗮𝘁𝗶𝗼𝗻 𝗶𝗻 𝗣𝗼𝘄𝗲𝗿 𝗦𝘆𝘀𝘁𝗲𝗺𝘀:

Relay coordination is a fundamental aspect of power system protection, ensuring that only the faulted section is isolated while the rest of the network continues operating reliably. It is essential for equipment safety, system stability, and minimizing power outages.

𝗖𝘂𝗿𝗿𝗲𝗻𝘁 𝗧𝗿𝗮𝗻𝘀𝗳𝗼𝗿𝗺𝗲𝗿 (𝗖𝗧):

➡️Measures line current and provides a scaled, proportional signal to protective devices.

➡️Serves as the primary sensing element, enabling accurate fault detection without exposing relays to high current levels.

𝗣𝗿𝗼𝘁𝗲𝗰𝘁𝗶𝘃𝗲 𝗥𝗲𝗹𝗮𝘆 (𝟱𝟬/𝟱𝟭, 𝟱𝟭𝗚):

➡️50 – Instantaneous Overcurrent Relay: Trips immediately for severe fault currents.

➡️51 – Inverse Time Overcurrent Relay: Operates with a time delay inversely proportional to fault magnitude.

➡️51G – Ground Fault Relay: Detects earth faults and initiates tripping.

➡️Acts as the decision-making element, determining whether and when to operate the breaker.

𝗖𝗶𝗿𝗰𝘂𝗶𝘁 𝗕𝗿𝗲𝗮𝗸𝗲𝗿 (𝟱𝟮):

➡️Receives the trip signal from the relay and interrupts current flow to isolate the fault.

➡️Ensures safe disconnection of the faulty section without affecting healthy portions of the system.

𝗣𝗿𝗶𝗻𝗰𝗶𝗽𝗹𝗲𝘀 𝗼𝗳 𝗥𝗲𝗹𝗮𝘆 𝗖𝗼𝗼𝗿𝗱𝗶𝗻𝗮𝘁𝗶𝗼𝗻:

➡️Downstream devices operate first; upstream devices provide backup.

➡️Time-current coordination ensures a proper operating sequence.

➡️Selectivity prevents unnecessary disconnection of healthy equipment.

𝗕𝗲𝗻𝗲𝗳𝗶𝘁𝘀:

✅ Enhanced system reliability and continuity of supply.

✅ Protection of transformers, feeders, motors, and other critical assets.

✅ Minimization of fault propagation and cascading outages.