Which ANSI/IEEE device numbers are associated with differential protection?

• 50,51

• 27,59

• 87,87T

• 21,32

• 67,68

A relay with device number 51 is designed for:

• Instantaneous overcurrent

• Time-delay overcurrent

• Underfrequency

• Voltage restraint

• Directional power

Which relay coordination method ensures selective tripping during faults?

• Overlapping time-current curves

• Zone-selective interlocking

• Differential current comparison

• Harmonic restraint

• Impedance-based grading

Device number 52 refers to:

• Circuit breaker

• Synchronous-check relay

• AC recloser

• Voltage regulator

• Auxiliary relay

Negative-sequence relays (device 46) are primarily used to detect:

• Phase-to-phase faults

• Ground faults

• Unbalanced loads

• Overvoltage

• Reverse power flow

Arc flash mitigation in switchgear can be achieved by:

• Using vacuum interrupters

• Installing current-limiting fuses

• Implementing zone-selective interlocking

• All of the above

• None of the above

The primary purpose of a switchboard’s dead-front design is to:

• Reduce harmonics

• Prevent accidental contact with live parts

• Enhance cooling efficiency

• Simplify maintenance

• Minimize voltage drop

Gas-insulated switchgear (GIS) uses which insulating medium?

• SF₆

• Nitrogen

• Vacuum

• Mineral oil

• Air

A draw-out circuit breaker design is preferred for:

• Ease of maintenance

• Cost reduction

• Harmonic filtering

• Surge suppression

• Grounding stability

Which standard governs low-voltage switchgear assemblies?

• IEEE C37.20.1

• IEC 61439

• ANSI C37.13

• NEMA KS1

• UL 1558