Differential relays are primarily used for the protection of which components against internal faults?

Differential relays are primarily designed to detect internal faults within electrical components by comparing the current entering and leaving the component. When there is an internal fault, such as a short circuit or ground fault, the current entering the component will differ from the current exiting it, triggering the relay. This characteristic makes differential relays particularly effective for a variety of components including transformers, induction motors, busbars, and alternators.

For transformers, differential relays can identify faults between the primary and secondary windings. In induction motors, they protect against ground faults or phase-to-phase faults within the motor's internals that may not be detected by other forms of protection. Busbars, which distribute electrical power, and alternators, which generate electrical power, are also at risk of internal faults that differential relays can promptly identify and isolate.

This broad applicability across multiple types of equipment confirms that differential relays play an essential role in the overall reliability and safety of electrical systems. Thus, the selection that states “All of the above” correctly aligns with the functions of differential relays, as they are integral in protecting transformers, induction motors, busbars, and alternators from internal faults.