Causes and Effects of Power Quality Disturbances

Power Quality Disturbances, Causes, and Impacts Impulse transient

Oscillatory Transient

Dips/Sags

Swells/Surges

Notching

a!e"orm Distortion

Transient Noise

#nder!oltage $%rownout&

Impulse Tr Transient ansient A sudden and short-duration disturbance caused by a very rapid ch ange in the steadystate condition of voltage, current, or both, that is unidirectional in polarity. Frequency range: >5 kH !high frequency" #uration: $%-&%% u'ec (o)-frequency transients: *5%% H #uration: *$% cycles Causes' Impacts'

+apacitor s)itching +ripping of A'#s and other sensitive equipent +/o +/oltage agnification at custoer capacitors

Oscillatory Transient A sudden and short-duration disturbance caused by a very rapid ch ange in the steadystate condition of voltage, current, or both, that is bi-directional in polarity.

(edium)"re*uency transients $+ -.) 0-.& #uration: * $ cycles" Causes'

+raveling )aves fro lightning ipulses +apacitor and circuit s)itching transients

Impacts' +Failure of custoer equipent

-igh "re*uency Transients 1 0-. Duration'  * %.5 cycle

+')itching on secondary systes Causes'

+(ightning-induced ringing +(ocal ferroresonance +0adiated noise ay disrupt sensitive electronic equipent

Impacts' +High rate of rise oscillations ay cause lo)-voltage po)er supplies to fail

+'hort-duration voltage variations

Dips #ecrease bet)een %.1 and %.2 pu in rs voltage or current at the po)er frequency for duration fro %.5 cycles to 1 inute Causes'

+(ocal and reote faults

Impacts' +#ropouts of sensitive custoer equipent

2oltage Swells/Surges 3ncrease to bet)een 1.1 and 1.4 pu in the rs voltage or current at the po)er frequency for durations fro %.5 cycle to 1 in

Causes'

Impacts'

+'ingle-line-to-ground faults +quipent overvoltage +Failure of 67/s forced into conduction +(ong-duration voltage variations

O!er!oltage 3ncrease in the rs ac voltage greater than 11%8 at the po)er fre quency for a duration longer than 1 in. +(oad s)itching off Causes'

+apacitor s)itching on +'yste voltage regulation

Impacts' +9robles )ith equipent that require constant steady-state voltage

#nder)2oltage #ecrease in the rs ac voltage to less than 2%8 at the po)er frequency for a duration longer than 1 inute

Causes' Impacts'

+(oad s)itching on +apacitor s)itching off +9robles )ith equipent that require constant steady-state voltage, syste voltage regulation

a!e"orm distortion / -armonics  onlinear loads, such as po)er electronic equipent, produce non-sinusoidal current )avefors )hen energied )ith a sinusoidal voltage. hey in;ect currents at haronic !integer ultiple of the fundaental frequency" frequencies into the syste. Haronic currents, and the voltage distortion they create as they flo) through the syste ipedance. Causes'

+onlinear loads +3proper operation of sensitive equipent

+0eduction of equipent operating reliability and service life !%-1%%th Impacts' haronic" +apacitor failures or fuse blo)ing +elephone interference

Notching 9eriodic voltage disturbance caused by the noral operation of po)er electronics devices )hen current is coutated fro one phase to another Causes' Impacts'

Noise

+oral operation of electronic equipent +3proper operation of equipent +quipent failure

Any un)anted electrical signals )ith broadband spectral content lo)er than &%% kH superiposed upon the po)er syste voltage or current in phase conductors, or found on neutral conductors or signal lines +3proper grounding Causes'

+oral operation of electronic equipent +Arcing devices +')itching po)er supplies

Impacts'

+3nterference )ith electronic devices such as icrocoputer and  prograable controllers