Which type of relaying is commonly used for transformer protection?

Differential relaying is commonly utilized for transformer protection due to its effectiveness in detecting faults within transformers while ignoring normal operational variations. This type of relaying continuously monitors the current entering and leaving the transformer. If a significant difference between the incoming and outgoing currents is detected, which would indicate a fault condition (such as a short circuit or internal failure), the differential relay promptly activates to isolate the transformer from the system, thereby preventing further damage.

The principle behind differential relaying relies on Kirchhoff's current law, which states that the sum of currents entering a junction must equal the sum of currents leaving. Therefore, under normal conditions, the currents should balance. When an internal fault occurs, this balance is disturbed, triggering the relay's protective actions.

This makes differential relaying particularly advantageous for transformer protection, as it is highly sensitive to internal issues and can distinguish between fault conditions and load changes, which is critical in maintaining system integrity and ensuring prompt fault isolation.