What is the IEEE device number specifically designated for a differential relay?

The IEEE device number designated for a differential relay is 87. Differential relays are used to detect differences in current between the input and output of a specific component, such as a transformer or generator. The primary function of these relays is to identify faults by comparing the currents at two or more locations; a significant difference in these currents typically indicates a fault condition within the protected zone.

This designation is part of a broader IEEE numbering system, which assigns specific numbers to different types of protective relaying devices to standardize identification across the industry. Understanding these designations is crucial for electrical engineers and technicians when discussing protection schemes and relay functionalities.

In this context, the other choices represent different protective relay functions. For instance, device number 86 corresponds to lockout relays, 67 refers to directional overcurrent relays, and 50 denotes instantaneous overcurrent relays. While all these relays serve important roles in our electrical systems, their specific applications and operational mechanisms differ significantly from those of differential relays, thereby reinforcing why 87 is the correct answer for this question.