Danfoss TTS350

4.14 Soft Start
Therearetwo(2)differentvariantsofcompressorSoftStarts.AllRevisionGandearliercompressorshadafactory
installedClosed-TopSoftStart.BeginningwithRevisionHcompressors,theOpen-TopSoftStartwasintroduced.
Thereisasignificantvisualdifferencebetweenthetwo(2)variants,refertoFigure4-94SoftStartVariantsforthe
visualdifferences.
TheOpen-TopSoftStartcanhandleallinputvoltages,whereastherearedistinctversionsoftheClosed-TopSoft
Startstohandlespecificvoltages.IfaClosed-TopSoftStartmustbereplaced,DanfossLLCoffersconversionkitsto
allowtheuseoftheOpen-TopSoftStart.RefertotheSparePartSelectionGuideforTTS/TGScompressorsforkit
details.
Figure 4-94 Soft Start Variants
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TheSoftStartlimitsin-rushcurrentwhenpowerisappliedtothecompressorbyprogressivelyincreasingthe
conductionangleofthevoltagethroughtheSCRstochargetheDCcapacitors.Itusesa3-phasevoltageinputat
50/60Hz,between380-575VAC,andaDCvoltagesignalfromtheSCRoutputtogenerateoutputpulsesof0-12VDC
totheSCRgatesforthein-rushcurrentcontrolsignal.
ForClosed-TopSoftStarts,the3-phaseACvoltageispassedthrough1/4Afast-actingfusestotwo(2)onboard
transformersthatreducetheprimaryvoltagetoasecondary15VAC.Bothtransformerspassthesecondaryvoltage
throughseparateNanofuses.ThesetransformerspowertheSoftStartandprovidethetriggersignalvoltagetothe
PottedDC-DCwhenDCbusvoltagelevelsreachtheminimumlevel.
TheClosed-TopSoftStartalsousesa2A1000VDCfusetopasshigh-voltageDCtotheDC-DCConverter.
ForOpen-TopSoftStarts,theMainsACvoltageispassedthroughresettablefusestoanon-boardisolatedDC-DC
converterduringtheinitialstartupstage.AfterDCbusvoltagereachesminimumlevel,theOpen-FrameDC-DC
converterbeginsprovidingvoltagetotheservicesidewithoutassistancefromtheSoftStart.
InadditiontomonitoringACmainsvoltageandtheHVDCbus,theOpen-TopSoftStartalsoprovidesanon-board
temperaturesensor,varistors,andEMIfiltersforsystemprotection.
AllDCvoltagesfromtheSoftStartarewithrespecttothepositiveDCbus,notthecompressorground.Referto
Figure4-95Closed-TopSoftStartConnectionsonpage114.andTable4-22Closed-TopSoftStartConnection
Identificationonpage114.fortheSoftStartconnectorlocationsandidentifications.
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