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Chapter: Power Quality : Introduction to Power Quality

Terms and Definitions- Power Quality

Power Quality - Introduction to Power Quality - 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.

 


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