Power Quality is the quality of the electric power supplied to electrical equipment . Poor power quality can result in misoperation of the equipment. There are many ways in which a power feed can be poor quality and so there is no single way to completelly quantify the quality of a power feed.

Ideally the power would be supplied as a sinewave with the amplitude and frequency given by national standards (in the case of mains ) or system specifications (in the case of a power feed not directly attached to the mains) with an impedance of zero ohms at all frequencies.

No real life power feed will ever meet this ideal, It can deviate from it in the following ways (among others).

• Variations in the peak or rms voltage (both theese figures are important to different types of equipment) When the rms voltage exceeds the nominal voltage by a certain margin, a surge is produced. A dip is the opposite situation: the rms volage is below the nominal voltage by a certain margin.
• Variations in the frequency
• Variations in the wave shape
• Quick and repetitive variations in the rms voltage. This produces flicker in lighting equipment.
• Nonzero low frequency impedance (if the appliance draws more power the voltage drops)
• Nonzero high frequency impedance (if the appliance demands a large amount of current or stops demanding it suddenly there will be a dip or spike in the voltage due to the inductances in the power supply line)
• rapid Spikes and dips and longer term variations in voltage (usually caused by the interaction of other equipment with line impedance)

See also

• Electricity distribution