IEEE defined power quality disturbances into seven categories based on wave shape:
1. Transients
2. Interruptions
3. Sag/ Under voltage
4. Swell/ Overvoltage
5. Waveform distortion
6. Voltage fluctuations
7. Frequency variations
1. TRANSIENTS
Potentially the most damaging type of power disturbance, transients fall into two subcategories:
1. Impulsive
2. Oscillatory
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2. INTERRUPTIONS
An interruption is defined as the complete loss of supply voltage or load current. Depending on its duration, an interruption is categorized as instantaneous, momentary, temporary, or sustained. more »
3. SAG/ UNDERVOLTAGE
A sag is a reduction of AC voltage at a given frequency for the duration of 0.5 cycles to 1 minute’s time. Sags are usually caused by system faults, and are also often the result of switching on loads with heavy startup currents. more »
4. SWELL/ OVERVOLTAGE
A swell is the reverse form of a sag, having an increase in AC voltage for a duration of 0.5 cycles to 1 minute’s time. For swells, high-impedance neutral connections, sudden (especially large) load reductions, and a single-phase fault on a three-phase system are common sources. more »
5. WAVEFORM DISTORTION
There are five primary types of waveform distortion:
1. DC offset
2. Harmonics
3. Interharmonics
4. Notching
5. Noise
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6. VOLTAGE FLUCTUATIONS
A voltage fluctuation is a systematic variation of the voltage waveform or a series of random voltage changes, of small dimensions, namely 95 to 105% of nominal at a low frequency, generally below 25 Hz. more »
7. FREQUENCY VARIATIONS
Frequency variation is extremely rare in stable utility power systems, especially systems interconnected via a power grid. Where sites have dedicated standby generators or poor power infrastructure, frequency variation is more common especially if the generator is heavily loaded. more »
