Electric power quality

Electric power quality is the degree to which supply voltage, frequency, and waveform stay within specified limits and avoid disturbances that disrupt equipment.

Voltage sag: A temporary reduction in RMS supply voltage, typically lasting from a fraction of a second to several seconds. Short voltage drops are among the most common disturbances behind equipment trips and resets.
IEEE 1159: An IEEE recommended practice defining monitoring and classification of power-quality phenomena. Its event categories provide a common framework for describing disturbances.
Alternating current: Electric current that periodically reverses direction, commonly supplied as a sinusoidal waveform. Its changing waveform is the basis for specifying AC supply quality.
Electric power reliability: The likelihood that an electric power system delivers service continuously and adequately over time. Reliability concerns whether power is available; quality concerns the characteristics of delivered power.
Voltage swell: A temporary increase in RMS supply voltage above its normal range. Overvoltage events can stress insulation and damage sensitive electronic loads.
IEC 61000: A family of international standards addressing electromagnetic compatibility, including emissions and immunity. Its requirements connect disturbance limits with equipment compatibility and testing.
Voltage: The electric potential difference between two points, measured in volts. Supply-voltage magnitude is one of the central quantities assessed for quality.
Power system stability: The ability of an electric power system to return to an acceptable operating state after a disturbance. Stability describes system-wide dynamic behavior rather than the quality experienced at a supply point.
Harmonic distortion: Deviation of a periodic waveform from a pure sinusoid through the presence of integer-multiple frequency components. Nonlinear loads inject harmonics that deform the supply waveform and can overheat equipment.
Power quality analyzer: An instrument that records electrical quantities and identifies disturbances such as sags, transients, and harmonics. These instruments reveal which events occur and whether supply limits are exceeded.

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