Operating Gas Generator Sets in Island Mode
Whateverthereasons,thesetrendshavepusheduserstoconsiderapplyinggasgensetpackagesintoapplicationsthathavetraditionallybeenlimitedtodieselpackages.Specifically,I'mreferringtousinggasgensetsin"standby"or"islandmode"typeapplications,wheretheunitsoperatewithoutbeingparalleltothelocalutilitygrid.Butasmanyofushavelearned,thereareinherentchallengesassociatedwithusingagasolinegeneratorinan"offthegrid"typesetting.HereareafewofthelessonsI'velearnedfrommyyearsofexperienceinthisarea:
Firstoff,whenitcomestotransientresponse,gasgensetsarenotdiesels.
Therearecoredifferencesthatdriveverydifferentperformancewhenitcomestoacceptingandrejectingloads,particularlywhenoperatingoffthegrid.Generallyspeaking,agasenginewillhavelessloadpickup(transient)capabilitythanadieselbothintermsofhowlargealoadsteptheunitcantakeandhowlargethevoltage/frequencydeviationwillbe.Second,recoverytimeafteraloadstepisalsolongerforagasengine.Evenatthesteadystatecondition(noloadchange),youwilloftenseelessfrequencystabilityonagasunitwhencomparedtoadiesel.Thisisnotalltosaythatgaspackagescan'tbesuccessfullyappliedinislandmodeapplications,butitisimportanttounderstandtheapplicationandmanageexpectations.
Notallgasolinegeneratorsarethesame.
Manymarketsdemandloweremissions,betterfueleconomy,andhigherpowerdensity.Tomeetthesegoals,manyengineplatformshadtogiveupthesimpler,morerobustcontrolsystemsandoversizedairsystems.Thishowever,meantthelossoftransientcapabilitywhencomparedtotheirsuccessors.Generally,asfuelefficiencyincreases,thecapabilitytoacceptloaddecreases.Tocombatthistrend,someoftherecentplatformsoffernewcontroltechnology,specificallydesignedtoimprovetransientcapability.Thekeytosuccessfulapplicationisunderstandingthatdifferentplatformshavedifferenttransientcapabilityandtheunitshouldbematchedtoyourapplicationsneeds.
Don'toversimplify.
Genericindustrytermslikeislandmodeandstandbydonotdefineasetoftransientrequirements.Forexample,justbecauseaunitneedstooperateoffthegrid,doesn'tmeantheunitwillbesubjecttolargeloadstepsorhavetightvoltagevariationrequirements.Anothercommonoversimplificationistheblindapplicationofindustryspecifications.Thestandby/islandmodemarkethasbeentraditionallylimitedtodieselpackages,soitisnosurprisethatmanyindustryspecificationsarewrittenaroundthatproduct.
Details,details,details.
Intheend,theonlywaytoensurethatyouwillhaveasuccessfulapplicationistounderstandyourrequirementsdetailscreatethebigpicture.Thismayseemobvious,butyou'dbesurprisedhowmanytimesIgetaskedtoreviewanislandmodeapplicationwithouttheloadrequirementspelledout.Therearealotofdifferentfactorsthatcanaffectthetransientperformanceofagaspackage,andyouneedtotryandunderstandallofthemforasuccessfulgaspackageapplication.HerearesomeofthebestquestionsI'velearnedtoask:
1.Whatarethecriticaltransientcharacteristics?
Specifically,whatistheallowablevoltageandfrequencydeviation?Whatistherequiredrecoverytime?Thesevaluesarethenittygrittyofanytransientapplication.It'salsogoodtohaveanunderstandingastowhathappenswhenoneoftheserequirementsisn'tmet.Doesthisrepresentadelaynuisanceordamagetoamotor?
2.Whataretheloads?
Howmanyloadstepsareneeded,whattypesofloadsarebeingapplied,andwhatistheloadprofile/strategy?Oftentimes,howyouloadagasolinegeneratorcanhaveagreatereffectontransientperformancethantheunititself.Itisalsousefultounderstandifthereisanyflexibilityintheloadingstrategy.
3.Whataretheextraneousfactorsthatimpactaunit'stransientperformance?
Probablythemostimportantfactorisyourfueldeliverysetup.Whatistheavailablefuelpressure?Howmuchflowisavailable?Howsteadyisthefuelpressure?Howconsistentisthefuelquality?Emissionssettingandfueltypecanalsoplayaroleintransientcapability,alongwithanyderateforaltitudeandambienttemperatures.Mostgensetspecsheetshavepublishedmin./max.requirementsforthesetypesofparameters.Someislandmodespecificpackagesmayevenrecommendspecificvaluesfortheseparameterstooptimizetransientcapability.
Sothesearejustsomeofmyexperiences,butIknowtherearealotoffolksoutthereonthegroundatcommissioning,makingtheseunitsrunandpassthevariousloaddemotests.
Operating Gas Generator Sets in Island Mode
By: chinaqsh
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