A(n) ___ is a power quality event where there is a very brief period of reduced voltage, from sub-cycle to 60 cycles in length.

A(n) ___ is a power quality event where there is a very brief period of reduced voltage, from sub-cycle to 60 cycles in length.

• A. Swell
• B. Sag
• C. Ramp
• D. Under-voltage

Answer: (B)

A sag is a short-duration dip in the supply voltage, where the RMS level drops below the nominal voltage for a brief period—from a fraction of a cycle up to about one second (60 cycles at 60 Hz). This matches the description of a very brief reduction in voltage. Sags commonly occur when a large load starts, a transformer or line switches, or a temporary fault pulls voltage down. They’re different from a swell, which is a brief spike in voltage; a ramp, which is a gradual change in voltage over time; and under-voltage, which generally describes a sustained low voltage rather than a brief dip.

A sag is a short-duration dip in the supply voltage, where the RMS level drops below the nominal voltage for a brief period—from a fraction of a cycle up to about one second (60 cycles at 60 Hz). This matches the description of a very brief reduction in voltage. Sags commonly occur when a large load starts, a transformer or line switches, or a temporary fault pulls voltage down. They’re different from a swell, which is a brief spike in voltage; a ramp, which is a gradual change in voltage over time; and under-voltage, which generally describes a sustained low voltage rather than a brief dip.