Which standard device number does not match its correct description?

The choice regarding the standard device number that does not match its correct description is related to the definition and roles assigned to specific protective relay functions.

For power factor relay, the standard device number is actually 34, not 85. The purpose of a power factor relay is to monitor and control the power factor of an electrical system, which ensures efficient operation and can prevent issues related to poor power factor such as increased losses and demand charges.

In contrast, the other options accurately represent their respective relay functions:

• The phase-balance relay, designated as 46, is used to detect an imbalance in the phase currents, which can indicate potential faults in a three-phase system.

• The sync-check relay, assigned the number 25, is crucial for ensuring that two systems are synchronized prior to connecting them, thus preventing equipment damage.

• The AC directional overcurrent relay, which is designated as 67, identifies overcurrent conditions while also determining the direction of the fault current, playing a vital role in system protection.

Therefore, the mismatch in the description for the power factor relay highlights why it is the correct answer for the device number that does not align with the appropriate description.