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subject: Operating Gas Generator Sets in Island Mode [print this page]

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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