Terms and Definitions- Power Quality

Terms and Definitions:

1. Power Quality:

It is any deviation of the voltage or current waveform from its normal sinusoidal wave shape.

2. Voltage quality:

Deviations of the voltage from a sinusoidal waveform.

3. Current quality:

Deviations of the current from a sinusoidal waveform.

4. Frequency Deviation:

An increase or decrease in the power frequency.

5. Impulsive transient:

A sudden, non power frequency change in the steady state condition of voltage or current that is unidirectional in polarity.

6. Oscillatory transients:

A sudden, non power frequency change in the steady state condition of voltage or current that is bidirectional in polarity.

7. DC Offset:

The presence of a DC voltage or current in an AC power system.

8. Noises:

An unwanted electric signal in the power system.

9. Long duration Variation:

A variation of the RMS value of the voltage from nominal voltage for a time greater than 1 min.

10. Short Duration Variation:

A variation of the RMS value of the voltage from nominal voltage for a time less than 1 min.

11. Sag:

A decrease in RMS value of voltage or current for durations of 0.5 cycles to 1 min.

12. Swell:

A Temporary increase in RMS value of voltage or current for durations of 0.5 cycles to 1 min.

13. Under voltage:

10% below the nominal voltage for a period of time greater than 1 min.

14. Over voltage:

10% above the nominal voltage for a period of time greater than 1 min.

15. Voltage fluctuation:

A cyclical variation of the voltage that results in flicker of lightning.

16. Voltage imbalance:

Three phase voltages differ in amplitude.

17. Harmonic:

It is a sinusoidal component of a periodic wave or quantity having a frequency that is an integral multiple of the fundamental power frequency.

18. Distortion:

Any deviation from the normal sine wave for an AC quantity.

19. Total Harmonic Distortion:

The ratio of the root mean square of the harmonic content to the RMS value of the fundamental quantity.

20. Interruption:

The complete loss of voltage on one or more phase conductors for a time greater than 1 min.