Power Quality Performance events and disturbances

Events

Power Quality (PQ) events are short-term disturbances that are characterized by magnitude, duration, and direction.

The following table provides definitions for the different PQ events:

PQ Events	Summary	Magnitude	Source	Duration	Consequence
Interruptions	Loss of the supply voltage	Less than 10% of nominal	Utility or facility	½ cycle to 1 minute or more	Downtime
Voltage Sag	Decrease in voltage magnitude	90% to 10% of nominal voltage (typical)	Utility or large motors starting	½ cycle to 1 minute	Malfunction or downtime
Voltage Swell	Increase in voltage magnitude	110% to 180% of nominal (typical)	Utility or facility	½ cycle to 1 minute	Equipment malfunction or damage
Transient Voltage	Short-duration high overvoltage	Potentially several thousands of volts and amps	Switching activities or lightning strikes	<50 ns to 50 ms	Electronic equipment damage
Over Voltage	Sustained increase in voltage magnitude	110% to 120% of nominal (typical)	Utility or facility	More than 1 minute	Equipment malfunction or motor heating
Under Voltage	Sustained decrease in voltage magnitude	80% to 90% of nominal (typical)	Utility or facility	More than 1 minute	Equipment malfunction or damage

Power Quality event classifications

The following image illustrates the classification of events in relation to a CBEMA chart. The Power Quality Performance gadgets and reports follow this same color classification of Power Quality Events.

A	Percent of nominal voltage	B	No impact region	C	Transient	D	Swell
E	Over Voltage	F	Sag	G	Under Voltage	H	Interruption

Disturbances

Power Quality (PQ) disturbances are long-term disturbances.

The following table provides definitions for the different PQ disturbances:

PQ Disturbances	Summary	Magnitude	Source	Duration	Consequence
Voltage Unbalance	Non-symmetrical voltages	0.5% - 2.5% of nominal voltage (typical)	Utility or facility	Steady state	Overheating or malfunction
Current Unbalance	Non-symmetrical current	1.0% - 30% of nominal current (typical)	Utility or facility	Steady state	Malfunction and breaker trip
Voltage Harmonics	Waveform distortion	0 to 20% (typical)	Nonlinear loads	Steady state	Malfunction and overheating
Current Harmonics	Waveform distortion	0 to 20% (typical)	Nonlinear loads	Steady state	Malfunction and breaker trip
Frequency Variation	Deviation of the frequency from the nominal	Up to 5% deviation of nominal (typical)	Standby generators or poor power infrastructure	Intermittent	Malfunction or motor degradation
Flicker	Voltage waveform envelope variations	0.1% to 7% (typical)	Load exhibits significant current variations	Intermittent	Flickering lights, equipment malfunction