Como Medir El Voltaje de Salida de Un Variadr de Velocidad

7/29/2019 Como Medir El Voltaje de Salida de Un Variadr de Velocidad

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>>Wh rbshg h r sgs h r/drv sys,h f rs f p vs. p. A vrb-frqy drv (VFD)rsfrs h p s f s vg d frqy vg d fr-qy rg h b vrd r r rq.

rbshg h p srs h sg pr sppy d qy. rb-shg h p srs h srg h rsfrd vg d frqy.Ts r sps hrgh h sr sq fr ssssg VFD p:t%$#VTt0VUQVUWPMUBHFDVSSFOUGSFRVFODZt6OCBMBODFt7PMUTIFSU[SBUJPt0VUQVUSFnFDUJPOT

Figure 1JMMVTUSBUFTUIFDPNQPOFOUTPGB7'%JOQVU"$UP%$DPOWFSUFSBOEPVUQVUps dh dd (PWM) TJHOBMXJUIUIF%$MJOLJOCFUXFFO*OB7'%UIFPWM vrr rgs bh vg andfrqy h r. T vg d

3188830$,8&--"650."5*0/$0.5)&+063/"- "13*-]5)&+063/"-

HOW TO MEASUREOUTPUT VOLTAGEFROM A VFD TO A MOTORLearn the step-by-step measurement sequence for assessing variable-frequencydrive output factors when troubleshooting electrical signals.

Figure 1. Envisioning a motor/drive system as three segments input, output and load helps clarify what specific measurements and troubleshooting

steps to take in each segment.
http://www.rockwellautomation.com/thejournalhttp://www.rockwellautomation.com/thejournal


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frqy h r s vrd bydg h dh f h ppss, hh s pshd by -rg h sdr sh.

T p dds prvd sDC bffr fr h shg vrrs, qv 1.414 s hp f h p vg. T p-r s s fir rd rpp h DC s.

T r dvs h vrrs sy r sd g bp-r rssrs (IGB), d dyshv gh pr hd ds p 500 hp.

Step 1: Measure DC BusVoltageA ssp b sd -sr h bs v f h rfid

DC vg; h AC pd, s b sd z hsg v h x f rpp (sFigure 2).t.FBTVSFUIF%$CVTWPMUBHF

rss h + d rs sgPTDJMMPTDPQFPS%..t6TF"$PS%$JOQVUDPVQMJOH

sr h bs r rppvgs.t.BLFTVSFUIFTDPQFBOEQSPCF

r rd pprpry srh vg v.

Interpreting DC BusMeasurementsT DC bs vg s rv hp vg f h s p.t%$CVTWPMUBHFJT_YUIF

rs vg. Fr xp,fr 480VAC drv, h DC bsTIPVMECF_7%$tA DC voltage value that is too

low can cause the drive to trip.

At the cause, the mains input

voltage is probably too low, or

the input sine wave might be

distorted by flat topping.

t*GUIFSJQQMFTQFBLTIBWFBEJGfr rpv v, fh rfir dds s pssbyfg (hs s d

dpd). Rpp vgsbv 40V b sd byfg prs r drv rg h s s frh d r d d(s Figure 3).

Step 2: Measuring Voltageand Unbalancet6TFBOPTDJMMPTDPQFXJUIB718.GVODUJPODPOOFDUFECF-

h hr r rs(s Figure 4).t$PNQBSFUIFTDPQFSFBEJOHTUPUIFESJWFTEJTQMBZWBMVFTt7PMUBHFESPQCFUXFFOESJWFBOE

r rs shd xd 3%.t6OCBMBODFHSFBUFSUIBOJT

prb.t6TFBNVMUJDIBOOFMPTDJMMPTDPQFUP

h fr r vg brss h hr p phss.t.FBTVSFUIFWPMUBHFPOFBDIUFS-

, d rrd h srdvg fr s h x sp.t.FBTVSFWPMUBHFVOCBMBODFBU

f d.

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+ DC -

Figure 2. Connecting an oscilloscope to mea-

sure negative DC and positive DC buffer voltage.

Figure 3. These show an example of DC-coupled versus AC-coupled waveform traces from an oscilloscope used to inspect overall DC and

ripple voltages.


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Step 3: Measuring CurrentUnbalanceUs ssp h rrp hr drv p

rs spry sr hrr dr h r (sFigure 5).

Bs h rr sr b d hgh-rgy, r-y sy vr, b sr sh prpr rr p. If yr ssp ds y vb, s h sidebar pg 34b y g b.

T v f b shd

xd 10%.t'PSFWFSZPGWPMUBHFVOCBM, r rr b b 3% 4%.t*GWPMUBHFVOCBMBODFJTMPXUIFO

xssv rr b dd shrd r dgsr phss shrd grd.t(FOFSBMMZDVSSFOUVOCBMBODFGPS

hr-phs rs shd xd 10%.t7PMUBHFVOCBMBODFXJMMSFTVMUJO

rr b.t*GUIFWPMUBHFVOCBMBODFJTXJUIJO

pb s, h y xssvrr b dd dd shrd r dgs rone of the phases shorted to ground.

Step 4: Volts/Hertz RatioT r f vg frqy,

srd hrz, drs h f rq prdd by ACd r. By pg hs rs, h g fid sd hr s p s v. Tsrss s rq.

Abv h frqy f60 Hz, h vg rs

yr, d h rq drs(s Figure 6). sr vs/hrz r, s

BEJHJUBMNVMUJNFUFSXJUIB718.PQUJPOXIFSF718.SFnFDUTUIFpd f h fd fr-qy, r ssp. T s-sp shd ssy dspyh frqy f h PWM pd vg prb h rp rg (s Figure 7).

Us rr p sr hGSFRVFODZ*UTIPVMECF_GPS7NPUPS_GPSB7NPUPS

Constant7.67 V/hz

Constant Torque

Vo

ltage(V)

Frequency (Hz)0 30 60

460

230

0

Extra Torqueat Start-Up

Vo

ltage(V)


460

230

0

ExtraTorquefrom Higher

Voltage

Vo

ltage(

V)


460

230

0

T1 T2 T3

T1

T2

T3

Figure 4. Use an oscilloscope with appropri-

ate safety-rated electrically isolated inputs to

perform differential measurement on the three-

phase output.

Figure 5. Measure the current through each

phase using appropriately rated current

clamps.

Figure 6. Voltage and frequency in constant-

torque variable horsepower applications can

be measured easily to verify proper drive

programming and motor operation.


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Step 5: Output Refl ectionsRfls r s rs f pd sh r hg h rr rsss ph (s

Figure 8). I r drv r,h p f h rfl d bs hgh s h DC bs vg v.

s gy, sdr hhpps grd sprr hh fl f r s ryhgd by s sppg

h rbbr hs. T prssr hsprr hd hgs, pgs h b-p prssr s rsd.Usg vry g b (>100

f.) s rs rflsg h gh, srb srss.

T rfl sf fss ssps ssp dspy rg f vfrs, pdsd drs. As r f hb,rfls r rss >50% f vg r prb.

O pssb s dsshrg h drs b

h r d vrr. Ahrs s rs h grd f

bg, hs rdg h pd- r shg Ivrr RdMrs h hghr sv f 1,600V r grr h

hsd h rss.Ms rfls r sd by

fs shg DC vg by hIGBs (dV/d). T IGB s f h drv h fs vry fs /ff sh. TIGB ps DC vg s PWM sg dv d.Ts ss vry hgh dvvgs vr vry shr (sh-g) , s rfrrd s dV/d.

T IGB hs b- fr-hdd ps fr hs. H-

T3

T2

T1

T1 T2 T3

Figure 7. Setup for connecting the oscillo-

scope input to measure output voltage and a

current clamp to measure output frequency.

CapturedWaveform

ToleranceEnvelope Voltage

WaveformFigure 8. Note the voltage spikes on the trailing edge of this pulse width modulated signal, as

captured by an oscilloscope.

>> Manually CalculateUnbalance

If you manually measured voltage or

current, the next step in determining

if there is a voltage unbalance is tocalculate the percentage unbalance.

t%FUFSNJOFUIFWPMUBHFPSDVSSFOU

average.

t$BMDVMBUFUIFMBSHFTUWPMUBHFPS

current deviation.

t%JWJEFUIFNBYJNVNEFWJBUJPOCZ

the average voltage or current and

multiply by 100.

This results in a percentage of volt-

age or current unbalance for the

supply voltage to the drive input.

Heres an example:

% unbalance = (Max deviation fromaverage V or I/average V or I) x 100

Example:

30 + 35 + 30 = 95

95/3 = 31.7 average current

35 - 31.7 = 3.3 maximum deviation

3.3/31.7 = .104

.104 x 100 = 10.4% current

unbalance

In this example, the current unbal-

BODFJT%FQFOEJOHPOUIF

rating and impedance of the circuit,

this either could be acceptable or

a big problem. If the load current

is close to the rated current for thecircuit, high levels of unbalance can

cause nuisance breaker tripping.

Consideration: A manual unbalance

calculation is a point-in-time determi-

nation of voltage or current unbal-

ance. A power quality analyzer will

show voltage or current unbalance

in real time, including any variations

in unbalance.


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vr, rss r vsb h h ssp ghd sg s shd .

Measuring and Interpreting OutputReflectionsMs dg rs d hv h sp r dfrqy bddh d shr, fs p r-ss. Fr hs rs, s ssp d h r rs s srd Fgr 3.

T B p r Figure 9 dsrs h xs-sv rfls ppr vfr v. Kg h prr dsr s hps rd h ssry dfy r s.

Minimal DowntimeDrg h s f r drv sys frsrqrs sysy prfrg ss d srs y ps h sys. Spfiy rgrdg prsppy, dffr b pr p d p dppy bh dffr sr hqs d v- rr h. Wh dg, hs -srs gd rbshg h r s,

brgg h sys p s qy s pssb.Fluke Corp. is a participating Encompass Product Part-

ner in the Rockwell Automation PartnerNetwork. Based in

Everett, Wash., Fluke Corp. manufactures, distributes and

services electronic test tools.

Fluke Corp.www.rockwellautomation.com/go/p-fluke

Rockwell Automation Encompass ProductPartner Program.www.rockwellautomation.com/go/tjencompass

Figure 9. This shows an oscilloscope screen capture of a PWM drive.

signal with excessive reflections (B input trace).

Engineers at item North America

can provide no-cost design

assistance for a wide range of

safety solutions in manufacturing,

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handling.

For additional information visit us

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or call us toll free at, 888.729.4500.

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Como Medir El Voltaje de Salida de Un Variadr de Velocidad

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