Eaton Cutler-Hammer Digitrip RMS 910 Instructions Manual

Also see for Digitrip RMS 910: Instructions Instructional Leaflet Instruction leaflet

I.L.29-889APage11Press and release the“Step”push-buttonuntiltheGreenpointerLEDhas stoppedatthe [PF]location. Thenextpress andreleaseofthe“Step”push-button will initiate a3-phasewaveformcaptureinternallyintheDigitrip andinturncalculateallTHDandindividualvalues.NoticethattwoGreen LEDs[THD]and[lA]arenow illuminatedshowingtheTHD percentageforphaseAcurrent.Ifthe“Step”push-buttonis now pressedandheldforabout 2seconds,the individual harmoniccurrentsthatmakeupthe THD value are displayed inpercentageofthefunda-mental.The“Step”push-buttonmay nowbe released.The display format isthatthelefttwodigitsshowthehar-monicnumber(up to the27th harmonic)andthe righttwodigit positions showthepercentageoffundamentalforthewaveformthatwascaptured.Eachvalueis displayedforabouttwoseconds. Thissequence will continue inawraparoundmode until the“Step”push-buttonis againpressed and releasedin which case thenextphase THDvalue is displayed. Againifthe“Step”push-button ispressed and heldfor2secondsand its individual har-monic contentdata forlBwillsimilarly be displayed.Awaveformcapture event and harmonicdatacalculationis accomplished by locally steppingtothe[THD]GreenLED from the[PF]LED. The second way istoremotelytrigger the waveformcapturevia a IMPACCcommunica-tion command.IMPACC Series III software screens areavailable to show waveformcaptureoscillographs ofeach phase as wellas bar graphsofthe magnitudes andindividual harmonic that make up the three-phase cur-rents. See Section 5.7Fig.4 RatingPlug1.2.1.4Harmonics[THD]TheDigitrip RMS910provides capabilitiestocalculateanddisplaythe THD(total Harmonic Distortion) forphasecurrents[la],[lb]and[lc].ThetermTHD is usedtodefinein percentageofthepower frequencycurrent,theamountofharmoniccurrentthatthe breaker is seeingor thesys-tem isexperiencing.Thiscanbeuseful in troubleshootingtodetectindividual breakercurrentloads that couldleadto systemproblems and early equipmentfailure.Theequation used forcalculating is:l2rms-ifTHD = x100%IfwhereIrms is thermscurrentofthe waveformand^isthe rms currentofthe fundamental frequencyFor example the THD calculation for a load having anequal rms valueoffundamental and thirdharmonic cur-rent wouldhave a THD valueof100 percent. This wouldbealarge value THDand wouldnotbe typical.Besides individually displaying the THDforlA,lBandlc,the Digitrip 910will also display the individual harmoniccurrentsuptothe 27th harmonic forlA,lBandlc.The local operation on the Digitrip toobserve this data isdone using the“Step” push-button on the front panel ofthe Digitrip.F:T*NEffective May 1997