Differential protection is a crucial element in safeguarding power system components, such as transformers, generators, and motors, against internal faults. This protection scheme operates on the principle of comparing the current entering and leaving the protected equipment.
Key Aspects of Differential Protection:
Current Comparison: Differential relays continuously compare the incoming and outgoing currents of the protected equipment. In a healthy state, these currents should be nearly equal, indicating that no internal fault is present.
Zone of Protection: Differential protection defines a specific zone of protection, typically encompassing the entire protected equipment. Any imbalance in current within this zone triggers the relay, signaling a potential fault.
Operation during Faults: When an internal fault occurs, such as a winding short circuit in a transformer, the current entering and leaving the equipment becomes unbalanced. The differential relay responds by issuing a trip signal to isolate the faulty section.
Harmonic Restraint: To enhance sensitivity and prevent unnecessary tripping during inrush conditions or external system disturbances, differential relays often incorporate harmonic restraint mechanisms. These restraints filter out high-frequency components that may mimic fault conditions.
Communication and Backup Protection: Differential relays may be part of a communication network, allowing them to coordinate with other protection devices. Additionally, backup protection schemes, such as overcurrent relays, are often employed to provide a secondary layer of protection in case of a failure in the differential protection system.
Transformer Differential Protection: In the case of transformers, differential protection is widely used to detect winding faults. The relay compares the currents at the primary and secondary windings, ensuring comprehensive coverage.
Differential protection plays a critical role in preventing catastrophic damage to power system components, contributing to the overall reliability and stability of the electrical grid.
