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ISA Northern CaliforniaSection, South Bay
October 14, 2003
Craig Chidester 909 288 7990
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AFDs and Their Effect ono!er "#a$it%
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What Kind of Power Quality Effects?
Power factor? PF = kW / kVA i!h "otor content "eans la!!in! PF #$$ P "otor% &'$V% ()* eff% ##(A
+#$$ P , $-.&'kW/ P / $-() = 0$-1kW
##(A , &'$V , #-.) / #$$$ = (&-0kVA PF = 0$-1kW / (&-0kVA = 0&-'* 2 F3 4ut 5 at actual load% "ore like .$* or less
PF is i"6ro7ed with AF8s to ($ (9* AF8s seen as resisti7e load
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What Kind of Power Quality Effects?
:nco"in! ;ine Wa7e
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What Kind of Power Quality Effects?
Volta!e sa!? ;tandard "otor starters allow '9$* inrush @Weak 6ower syste"s are affected 9$$ P "otor on #$$$kVA% 9-.9*B Cf"r '9$* C +9$$ / #$$$ C $-$9.9 = #(* sa! AF8 li"its inrush to ##$* +or #9$* ##$* C +9$$ / #$$$ C $-$9.9 = )* sa!
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What kind of Power Quality Effects?
ar"onic 8istortion
& AFDs, DC Dri'es, ( )s, DC *o!er s#**$ies +co *#ters,d#*$icators, fa-.s/ will ca#se c#rrent +and 'o$tage/ har onics
)ing$e *hase & 3 rd, th, etc +tri*$ens/ can ca#se transfor erne#tra$ cond#ctor o'erheatingThree *hase & th, 7 th, 11 th , 13 th, etc can ca#se e #i* enta$f#nctionsig #estions & 56o! #ch and 56o! #ch is too #ch
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What are ar"onics?
Definition:
Harmonics are integral multiples of some fundamentalfrequency that, when added together, result in adistorted waveform.
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What are ar"onics?
f(x) = sin(x) f(x) = sin(5x)5
+
The resulting wave shows a strong departure from the smooth waves comprising it:
f(x) = sin(x) + sin(5x)5=
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What are ar"onics?
In fact, any function may be constructed from asine wave and some number of its harmonics:
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Where do they co"e fro"?
The power company typically supplies a reasonablysmooth sinusoidal waveform:
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Where do they co"e fro"?
...but nonlinear devices will draw distorted waveforms,which are comprised of harmonics of the source:
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o""on sources of ar"onics
Lighting ballasts
!" systems
#$% and D% drives
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A dri7es and ar"onics
%onverter D% bus
&smoothing Inverter
Determine the line'sideharmonics
Determines load'sideharmonics
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A dri7es and ar"onics
Inverter
Determines load'sideharmonics
())(%T" *) L*$D'"ID(H$+#* I%":
Have implications for the motorinsulation and windings.
(ssentially have -ero effect onother equipment on the power system.
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A dri7es and ar"onics
%onverter D% bus
&smoothing
Determine the line'sideharmonics
LI ('"ID( H$+#* I%" %$ H$ (
)$+'+($%HI / ())(%T" * TH(!*0(+ "1"T(#:
Distribution transformers
"tandby generators
%ommunications equipment
"witchgear and relays
%omputers, computer systems
Diagnostic equipment
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A dri7es and ar"onicsTypical 2'step converter waveform:
Harmonic %ontentI3 4 55.36I7 4 8.9 6I;; 4 2.;
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ar"onics and transfor"ers
Transformer overheating and potentialinsulation failure result from severalconditions caused by harmonics:
Increased s>in and pro?imity effectsHarmonics circulating in the primarywinding
Increased hysteresis losses
Increased eddy current losses
D% in the primary windings
$)%$)%
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ar"onics and transfor"ers
$)%$)%
#any transformers are rated by@A factorB which simply describestheir ability to withstand harmonics.
Transformers may also be deratedto compensate for the additionalheating caused by harmonics.
Improved transformer designs havealso been developed, with oversi-ed
neutral busses, special cores, andspecially designed coils.
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ar"onics and 6owerDcorrection ca6acitors
!ower correction capacitors can causeseries and parallel resonance effects ona power system.
If a harmonic is generated which e?citesa system resonance, amplification of thatharmonic may occur.
%alculation of the harmonic resonance frequency for thesystem can give an indication of potential resonanceproblems.
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ar"onics and 6owerDcorrection ca6acitors
(C$#!L(:
$ssume a ;3 $ supply ?fmr,with a 3.736 impedance.
$lso assume 2 $ of power correction capacitors on the system
;3 $3.736
2 $%
The harmonic resonance frequency is defined by:
4 h r 4
> $ sc> $%
;3
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>eco""ended li"its D :EEE 9#(
The Institute of (lectrical and (lectronics (ngineers EI(((Fhas set recommended limits on both current and voltagedistortion in I((( 3;8';885.
oltage distortion limits EG low'voltage busF:
$pplication class THD EvoltageF
"pecial system 9 6
/eneral system 3 6
Dedicated system ;< 6
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>eco""ended li"its D :EEE 9#(
#$CI# # H$+#* I% % ++( T DI"T*+TI* in percent of I L
Individual harmonic number Eodd harmonicsF Isc IL ;; ;; h ;7 ;7 h 59 59 h 93 TDD
5< =.< 5.< ;.3
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Attenuation of ar"onics
!assive )ilters
#ethod: !rovide a low'impedance path to groundfor the harmonic frequencies.
Jenefits: #ay be tuned to afrequency between two prevalent harmonics
so as to help attenuate both.
%oncerns: Tuning the filters may be a labor'intensiveprocess.
)ilters are difficult to si-e, because they offer a path for harmonics from any source.
Kuite sensitive to any future system changes.
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Attenuation of ar"onics
$ctive )ilters
#ethod: In ect equal and opposite harmonics onto thepower system to cancel those generated byother equipment.
Jenefits: Have proven very effective in reducingharmonics well below required levels.
%oncerns: The high performance inverter required for theharmonic in ection is costly.
!ower transistors are e?posed to conditionsof the line, so reliability may be a problem.
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Attenuation of ar"onics
;5'pulse +ectifiers
#ethod: Two separate rectifier bridges supply a singleD% bus. The two bridges are fed from phase'shifted supplies.
Jenefits: ery effective in the elimination of 3 th and 7 th
harmonics."tops harmonics at the source.Insensitive to future system changes.
%oncerns: #ay not meet the I((( standards in everycase.Does little to attenuate the ;; th and ;9 th harmonics.
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Attenuation of ar"onics
; 'pulse +ectifier
#ethod: $n integral phase'shift transformer and rectifierInput which draws an almost purely sinusoidalwaveform from the source.
Jenefits: #eets the I((( standards in every caseM
$ttenuates all harmonics up to the 93th.
"tops harmonics at the source.
Insensitive to future system changes.
%oncerns: %an be e?pensive at smaller H!Ns
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o"6arison of wa7efor"s
2'pulse converter
;5'pulse converter
; 'pulse converter
note the level of distortionand steep current rise.
the waveform appears moresinusoidal, but still not verysmooth.
virtually indistinguishablefrom the source currentwaveform.
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