WHAT IS Electrical Power System Quality With Terms and Definitions

Listed below is the most important terms you should know before studying  about electrical power system quality.

What is..

Aswell
is defined as an increase to between 1.1 and 1.8 pu in rms voltage or current at the power frequency for durations from 0.5 cycle to 1 min.  DC Offset is defined of the presence of a dc voltage or current in an ac power system

Harmonics
are sinusoidal voltages or currents having frequencies that are integer  multiples of the frequency at which the supply system is designed to  operate termed the fundamental frequency; usually 50 or 60 Hz.

Interharmonics
is a Voltages or currents having frequency components that are not integer multiples of the frequency at which the supply system is designed to operate e.g., 50 or 60 Hz 


Impulsive Transient
 is a sudden, non–power frequency change in the steady-state condition of  voltage, current, or both that is unidirectional in polarity primarily  either positive or negative.

Interruption
is occurs when the supply voltage or load current decreases to less than  0.1 pu for a period of time not exceeding 1 min. Long-duration variation is encompass root-mean-square rms deviations at power frequencies for longer than 1 min. Notching is a periodic voltage disturbance caused by the normal operation of power electronic devices when current is commutated from one phase to another.

Noise 
is defined as unwanted electrical signals with broadband spectral content  lower than 200 kHz superimposed upon the power system voltage or current  in phase conductors, or found on neutral conductors or signal lines.


Oscillatory Transient 
is a sudden, non–power frequency change in the steady-state condition of  voltage, current, or both, that includes both positive and negative polarity values.

Overvoltage
is an increase in the rms ac voltage greater than 110 percent at the  power frequency for a duration longer than 1 min.


Power frequency variations 
are defined as the deviation of the power system fundamental frequency  from it specified nominal value e.g., 50 or 60 Hz.

Sustained Interruption 
is When the supply voltage has been zero for a period of time in excess  of 1 min in which a long-duration voltage variation is considered.

Short-duration voltage variations 
are caused by fault conditions, the energization of large loads which  require high starting currents, or intermittent loose connections in  power wiring.

Sag 
is a decrease to between 0.1 and 0.9 pu in rms voltage or current at the  power frequency for durations from 0.5 cycle to 1 min.

Transients 
has long been used in the analysis of power systemvariations to denote an  event that is undesirable and momentary in nature.

Undervoltage 
is a decrease in the rms ac voltage to less than 90 percent at the power  frequency for a duration longer than 1 min.

Voltage Imbalance 
or is also called voltage unbalance this is sometimes defined as the  maximum deviation from the average of the three-phase voltage or currents, divided by the average of the three-phase voltages or  currents, expressed in percent.

Voltage fluctuations 
are systematic variations of the voltage envelope or a series of random  voltage changes, the magnitude of which does not normally exceed the voltage ranges specified by ANSI C84.1 of 0.9 to 1.1 
pu.

Waveform distortion 
is defined as a steady-state deviation from an ideal sine wave of power  frequency principally characterized by the spectral content of the  deviation.