Which type of relay protects a generator, transformer and bus?

The differential relay is designed to protect equipment such as generators, transformers, and buses by detecting differences in the current entering and exiting the equipment. This type of relay continuously monitors the current flow on both sides of the equipment. Under normal operating conditions, the current entering should equal the current exiting; any significant difference indicates a fault, such as a short circuit or internal failure within the equipment. When such a fault is detected, the differential relay will trigger the circuit breaker to isolate the faulty section, thus protecting the equipment from further damage.

This protective mechanism is crucial for generators and transformers, where internal faults can lead to severe consequences if not addressed promptly. Similarly, it protects buses, which are points of connectivity in the electrical network, from faults that may arise from connected equipment. The differential relay functions effectively in these roles due to its sensitivity to current imbalances, making it suitable for complex systems where multiple phases and connections are involved.

In contrast, the other types of relays serve different protective functions: overcurrent relays react to excess current; distance relays measure impedance to determine fault location; and voltage relays monitor voltage levels, which are essential but do not provide the specific protection needed for internal equipment faults that a differential relay does.