StaticElectricityandChargeAccumulationStaticelectricity&chargeaccumulationDefinitionsTypesofdischargesMechanismsofchargeaccumulation–fluidsystems-Streamingcurrent–SolidshandlingBalanceofchargesBondingandgroundingCasestudiesDefinitions-TypesofmaterialsConductive–Amaterialincapableofretainingasignificantelectrostaticchargewhenincontactwithearthandhavingavolumeresistivelyequalorlowerthan104Ω•mDissipative–Amaterialincapableorretainingasignificantamountofelectrostaticchargewhenincontactwithearthandhavingavolumeresistivityhigherthan104Ω•mbutequaltoorlowerthan109Ω•mmeasuredatambienttemperatureand50%relativehumidity.Non-conductive–Amaterialhavingavolumeresistivityhigherthan109Ω•mSparkdischargesDischargingofstaticelectricitybetweentwoconductors.SparkDischargeGenerationofSparkDischarges.–Chargeaccumulationataconductiveobject.–Fieldstrengthexceedstheelectricstrengthoftheambientatmosphere.Ignitability--gases,vapors,dustsEnergytransfer--upto10,000mJBrushdischargeBrushDischargeGenerationofBrushDischarges–Conductiveelectrodemovestowardsachargednonconductiveobject.Nonconductiveliningorsurfacemusthaveabreakdownvoltagegreaterthan4kVandathicknessgreaterthan2mm.Nonconductivecoatingcanbealayerofthepowderedsolid.Ignitability--gases,vaporsEnergytransfer--upto4mJPropagatingBrushDischargePropagatingBrushDischargeGenerationofPropagatingBrushDischarge–Bipolarchargingofthehighresistivitymaterial(nonconducting)thatislininganotherconductor.–Fieldstrengthexceedstheelectricstrengthofthehighresistivitymaterial.Nonconductingliningmusthavebreakdownvoltagegreaterthan4kVIgnitability--gases,vapors,dustsEnergytransfer--upto100,000mJMajorcontributortostaticelectricityignitions.ConeDischargeConeDischargeGenerationofConeDischarge.–Vesselslargerthan1m3.–Relativelyfastfillingrate,greaterthan0.5kg/s.–Highresistivity(>1010Ωm)bulkproduct,largerthan1mmdiameter.–Chargeaccumulationinthebulkproduct.–Fieldstrengthexceedstheelectricstrengthoftheambientatmosphere.Ignitability--gases,vapors,dustsEnergytransfer--upto1000mJIgnitabilityofdischargesTypeofDischargeEnergytransferIgnitabilitySpark<10,000mJgases,vapor,dustsBrush<4mJgases,vaporPropagatingBrush<100,000mJgas,vapor,dustsCone<1,000mJgas,vapor,dustsCorona<0.1mJsomegaseswithlowMIEStaticelectricity&chargeaccumulationDefinitionsTypesofdischargesMechanismsofchargeaccumulation–fluidsystems-Streamingcurrent–SolidshandlingBalanceofchargesBondingandgroundingCasestudiesChargeAccumulationWhenevertwodissimilarmaterialscomeincontact,electronsmovefromonesurfacetotheother.Asthesematerialsareseparatedandmoreelectronsremainononesurfacethantheother,onematerialtakesonapositivechargeandtheotheranegativecharge.MechanismsforChargeAccumulation:–ContactandFrictional–Doublelayer–Induction–TransportContactandFrictionalChargingDusttransport–e.g.pneumatictransportofpowders/solidsPouringpowders–e.g.pouringsolidsdownchutesortroughsGearsandbelts–e.g.transportingchargesfromonesurfacetoanotherDoublelayerchargingCausedbyfrictionandmovementatinterfacesonamicroscopicscale.–Liquid-liquid–Solid-liquid–Solid-solid–Gas-liquid–Gas-solidInductionchargingWhenanisolatedconductorissubjecttoaelectricfieldachargepolaritydevelopsontheobject.Iftheobjectisgroundedthenthechargesclosesttothegroundingsourceflowsawayleavingthebodywithanetchargeofoppositesign.ChargingbyTransportResultsf...
优质VIP
