Editing Power factor (section)

=== Distortion in three-phase networks ===
In practice, the local effects of distortion current on devices in a [[Three-phase electric power|three-phase distribution network]] rely on the magnitude of certain order harmonics rather than the total harmonic distortion.

For example, the [[Harmonics_(electrical_power)#Even%2C_odd%2C_triplen_and_non-triplen_odd_harmonics|triplen]], or zero-sequence, harmonics (3rd, 9th, 15th, etc.) have the property of being in-phase when compared line-to-line. In a [[delta-wye transformer]], these harmonics can result in circulating currents in the delta windings and result in greater [[Joule heating|resistive heating]]. In a wye-configuration of a transformer, triplen harmonics will not create these currents, but they will result in a non-zero current in the [[Ground and neutral|neutral wire]]. This could overload the neutral wire in some cases
and create error in kilowatt-hour metering systems and billing revenue.<ref>{{Citation | chapter-url = http://www.pge.com/includes/docs/pdfs/mybusiness/customerservice/energystatus/powerquality/harmonics.pdf | title = Power System Harmonics | publisher = Pacific Gas and Electric | chapter = Single-phase load harmonics vs. three-phase load harmonics | access-date = 2013-11-26 | archive-date = 2015-09-24 | archive-url = https://web.archive.org/web/20150924072113/http://www.pge.com/includes/docs/pdfs/mybusiness/customerservice/energystatus/powerquality/harmonics.pdf | url-status = dead }}</ref><ref>{{Citation | chapter-url = http://energylogix.ca/harmonics_and_ieee.pdf | title = Harmonics and IEEE 519 | publisher = EnergyLogix Solutions | chapter = Harmonic Effects | place = [[Canada|CA]] }}</ref>  The presence of current harmonics in a transformer also result in larger [[eddy currents]] in the magnetic core of the transformer. Eddy current losses generally increase as the square of the frequency, lowering the transformer's efficiency, dissipating additional heat, and reducing its service life.<ref>{{Citation |url=http://ecmweb.com/power-quality/effects-harmonics-power-systems |title=Effects of Harmonics on Power Systems |first=C. |last=Sankaran |year=1999 |publisher = Electro-Test |section=Transformers}}</ref>

Negative-sequence harmonics (5th, 11th, 17th, etc.) combine 120 degrees out of phase, similarly to the fundamental harmonic but in a reversed sequence.  In generators and motors, these currents produce magnetic fields which oppose the rotation of the shaft and sometimes result in damaging mechanical vibrations.<ref>{{Citation |url=http://ecmweb.com/power-quality/effects-harmonics-power-systems |title=Effects of Harmonics on Power Systems |first=C. |last=Sankaran |year=1999 |publisher=Electro-Test |section=Motors |quote=The interaction between the positive and negative sequence magnetic fields and currents produces torsional oscillations of the motor shaft. These oscillations result in shaft vibrations.}}</ref>