POWER QUALITY – EVENTS AND PARAMETERS
Power Quality is used synonymously with supply reliability, service quality, voltage quality, and quality of supply. IEEE defines it as "the concept of powering and grounding sensitive equipment in a manner that is suitable to the operation of that equipment." IEC 61000-4-30 defines it as "Characteristics of the electricity at a given point on an electrical system, evaluated against a set of reference technical parameters."
In general, power quality is related to disturbances in voltage, current, frequency, and power factor. Poor power quality means there is ample deviation from norms in the power supply that may cause equipment malfunction or failure.
Power Quality Events
- Interruptions: A condition in which the voltage at the supply terminals is close to zero — lower than 1% of declared voltage per IEC, lower than 10% per IEEE.
- Under Voltages (Sags/Dips): Short duration under voltages are called voltage sags or voltage dips. A supply voltage dip is a sudden reduction to a value between 90% and 1% of the declared voltage, followed by a recovery between 10 ms and 1 minute later.
- Over Voltages (Surges/Swells): Overvoltages of very short duration and high magnitude are called transient over voltages, voltage spikes, or voltage surges. Overvoltages within a duration of about 1 cycle and 1 minute are called voltage swells.
- Transients: Impulsive transients are sudden, non-power frequency changes that are unidirectional in polarity. Oscillatory transients are sudden changes that include both positive and negative polarity values.
- Voltage Unbalance: The maximum deviation from the average of the three-phase voltages or currents, divided by the average, expressed in percent.
- Waveform Distortion: A steady-state deviation from an ideal sine wave, with five types: DC Offset, Harmonics, Interharmonics, Notching, and Noise.
- Power Frequency Variations: Deviation of the power system's fundamental frequency from its specified nominal value (e.g., 50 Hz or 60 Hz).
- Voltage Fluctuations: Systematic variations of the voltage envelope whose magnitude does not normally exceed 0.9 pu to 1.1 pu. Loads with continuous, rapid variations in load current magnitude can cause voltage variations referred to as flicker.
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