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Understanding Power Quality

by: Fredy Okuneva

Understanding Power Quality ECE 528

Fredy Okuneva
GPA 3.81

Paul Ortmann

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Paul Ortmann
Class Notes
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This 9 page Class Notes was uploaded by Fredy Okuneva on Thursday October 22, 2015. The Class Notes belongs to ECE 528 at University of Idaho taught by Paul Ortmann in Fall. Since its upload, it has received 57 views. For similar materials see /class/227720/ece-528-university-of-idaho in ELECTRICAL AND COMPUTER ENGINEERING at University of Idaho.

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Date Created: 10/22/15
Universityofldaho ECE 528 Understanding Power Quality httpwwweoe uidahoedueepowerECE528 Paul Ortmann portmannuidahoedu 2087337972 voioe 2087363248 fax Lecture 23 Universityofldaho Today 0 Harmonic control devices Inine reactors chokes Zigzag transformers Passive filters Active filters Designing a harmonic lter Lecture 23 2 Universityofldaho Inline reactors chokes 0 Simply a series inductance Presents a series impedance that A is directly proportional to a v frequency Forces DC bus capacitor to charge more slowly r Additional benefit 0 Reduces DC bus overvoltages due to capacitor switching transients reduced nuisance tripping Lecture 23 Universityofldaho Inline reactors chokes o Sizing the inline reactor Line reactors are typically described as a 3 reactor 3 to 5 are common Size is based on the VA base of the drive Vbase 2 X 005 L75 VAb ase Inductance in Henrys is based on XL at the fundamental frequency Lecture 23 Universityofldaho Zigzag transformers Used for zerosequence currents Commercial facilities singlephase nonlinear loads Provides a path for zerosequence currents between the phase and neutral conductors Useful in existing facilities Lecture 23 5 Universityofldaho Passive filters 0 Capacitors and inductors can be arranged to produce high or low impedances at certain frequencies 0 Resistors can be added to provide damping o Shunt passive lters provide a low impedance alternate path 0 Series passive filters increase the series impedance for certain frequencies Lecture 23 E Universityofldaho Passive filters 0 Shunt passive lters Notch filter is the most popular May employ delta or wye connected capacitors connected to the line or neutral through inductors xix 3 Lecture 23 7 Universityofldaho Passive filters 0 Series passive filters Provide a high impedance to the target harmonic Must carry full load current Not practical for multiple harmonics Useful in singlephase applications Lecture 23 E Universityofldaho Lowpass broadband filter 0 Combines shunt and series elements Low impedance for low frequencies Hi impedance for high frequencies See PSQ p258 Several basic building blocks of the lowpass filter can be placed in series to produce a steeper slope in the frequency response Lecture 23 a Universityofldaho General approach with passive filters 0 Start at the lowest harmonic of concern 0 Tune filters slightly lower than the target harmonic 0 Check for resonant points creating high impedances o If system impedance changes reevaluate lter Lecture 23 in Universityofldaho Active filters 0 Use powerelectronics to inject the missing current in the nonlinear oad s current waveform 0 Results in minimal distortion on the source side 0 No resonance concerns 0 May also correct power factor and icker Lecture 23 ll Universityofldaho Filter desngn example FPQ p 249256 Goals improve displacement power factor and filter 5 11 harmonic Load is 480V 3ph 1200kVA DPF075 lag Load current has 25 5 11 harmonic We can address both the low power factor and the high 5th harmonic current with a shunt filter Note both texts contain this example and both contain errors they re corrected here References are to the FPQ text Lecture 23 12 Universityofldaho Filter design procedure Pick tuned frequency Calculate VAR requirements Calculate reactor size Determine filter duty requirements 2 gt Fundamental W L Harmonic RMS current and peak voltage Check capacitor ratings Calculate filter frequency response check for resonance at other harmonics Lecture 23 is Universityofldaho Filter design example Notch will be at 47 11 harmonic or 282Hz VAR requirement to improve DPF to 96 is 53223kVAR Error top of p 251 Compute capacitive reactance wye of the filter based on VAR need 0434 ohm eq 721 Capacitive reactance of the filter s capacitors is higher because inductive reactance will cancel some eq 722 Lecture 23 M Universityofldaho Filter design example Capacitive reactance 0454 ohms eq 724 Capacitive reactance and voltage rating determines kVAR 507kVAR at480V eq 725 792kVAR at 600V We39ll use 450kVAR at 480V as a rst try Filter reactor s fundamental inductive reactance is calculated from capacitor size and harmonic number 2 Xcap SSW 05129 eq39 73926 ARcap Lecture 23 is Universityofldaho Filter design example Inductance at fundamental 006148mH 480V capacitors Duty requirements We compute the fundamental and harmonic voltage and current for the capacitors separately then add these values to get the total RMS current and peak voltage Note eq 734 Load characteristic is not changed by filter So we still use 1200kVA to calculate current here Lecture 23 16 Universityofldaho Filter design example 0 Notes on duty calculations Fundamental duty is straightforward o Depends only on net filter reactance and the line Harmonic duty 0 Includes harmonic current from load AND source 0 Reactance calculations are at the harmonic frequency Total duty 0 Sum of fundamental and harmonic duty Lecture 23 17 Universityofldaho Filter design example Check capacitor rating limits Table 73 in text is based on IEEE standards 0 Capacitor kVAR limit was exoeeclecl We would probably want to try this again with 600V capacitors Check parallel resonance below notch frequency 0 2382Hz 397quot harmonic nearly the 4quot which 39s acoeptable because 4m harmonic distortion is normally low Check effect of component variations Lecture 23 18


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