___ is the short time reduction in the rms voltage between 0.1 to 0.9 p.u for a duration of ___

• A. Voltage sag, greater than 1 minute
• B. Voltage swell, 0.5 cycle to 1 minute.
• C. Voltage swell, greater than 1 minute
• D. Voltage sag, 0.5 cycle to 1 minute.

Answer: (D)

Voltage sag:
It is usually associated with system faults but can also be caused by energization of heavy loads or starting of large motors.
Voltage sag is the short reduction in the RMS voltage between 0.1 to 0.9 pu for a duration of 0.5 cycle to 1 minute