Drive Harmonics

8/10/2019 Drive Harmonics

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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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:nco"in! ;ine Wa7e


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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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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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%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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$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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;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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; '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.

Drive Harmonics

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