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Measures of Power Quality (1)

Measures of Power Quality (1). Displacement Power Factor (Displacement Factor)  = Cosine of phase shift between fundamental component of line current and the associated phase voltage (ie I A and V AN )

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Measures of Power Quality (1)

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  1. Measures of Power Quality (1) • Displacement Power Factor (Displacement Factor) •  = Cosine of phase shift between fundamental component of line current and the associated phase voltage (ie IA and VAN) • Accounts for proportion of fundamental current that does something useful.  = 1 is good,  = 0.5 is bad (50% of fundamental current does nothing useful) • Distortion Factor •  = RMS fundamental current/total RMS current • Accounts for the proportion of RMS current that is due to harmonics.  = 1 is good (pure sinewave).  = 0.5 is bad (50% of RMS current is due to the harmonics) • Power Factor • pf = power delivered/total RMS volts * total RMS amps • Tells us what proportion of the total apparent power (VA) represents useful power delivered to the load (Watts) • pf=1 is good, pf = 0.5 is bad (have to supply 1000VA to get 500W for example)

  2. Measures of Power Quality (2) • Relationship between quantities • Assume voltage is undistorted compared to current – normally reasonable for a decent power system • Then total RMS voltage = fundamental RMS voltage Power factor = Displacement factor * Distortion factor Note if the current is undistorted then  = 1 and Power factor = Displacement factor = Cosine of phase shift (as given in 1st year notes)

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