SF6 - Electrical Part Manual S

.comSF6www.ElectricalPartManualsuniversal technologyfor medium voltage3 to 40.5 kVmastering electrical power

.comualsantMarlPcatriwww.ElecIn the high voltage sector, SF6 hasbecome the accepted gas forswitchgear manufacturers : which dielectric is used in all extrahigh voltage metal-clad substations?SF6. which breaking technique is usedalmost exclusively today at extra highvoltage ?Breaking by puffer technique in SF6. which inert dielectric is used incompact MV/LV substations?SF6.SF6 is approved unanimously.All the major manufacturers in theworld - in the United States, Europeand Japan - have chosen SF6 as thepreferred insulating and breaking gas.Specialising in electrical powerdistribution sinc;e 1920, Merlin Gerinwere pioneers.At extra high voltage, in the earlydays, Merlin Gerin was first in theworld, in 1965, to run successful tests,at the Electricite de France laboratory,on the first bay of 220 kV metalcladequipment insulated by SF6.The success of SF6 at extra highvoltage led Merlin Gerin to developthis same technique at mediumvoltage. After more than 15 years ofindustrial experience we offer a widerange of reliable high-performanceequipment to meet the requirements ofworldwide public and industrialdistribution systems from 3 to 40.5 kV.

.com19711983First SF6 circuit breaker :the Fluarc F, designed for 24 kV publicdistribution substations.A decisive year : the RM6, a unanimously acceptedring main unit, revolutionizes thedesign and operation of transformersubstations, the Fluarc FG1, smallest breaker inthe world with the use of the rotatingarc technique, the Fluarc FG2 reaches 50 kA withthe same operating mechanism thanksto the thermal expansion effect.ualsSF6moves intoall medium voltageelectricaldistribution markets1974A world first; for secondary andtransformer substationsMerlin Gerin offers an SF6 circuitbreaker, the Fluarc FB.1975an1987ar1977tM this is innovation ; applying the SF6technique to switches with theVercors M6 for MV/LV transformersubstations. the Fluarc FB circuit breakerbecomes available for systems with arated voltage of 36 kV.calPA new breaking technique, the rotatingarc in SF6, gives rise to the Rollarccontactor designed for the control andprotection of medium voltage motors.1979The withdrawable Fluarc FG2 is addedto the range of puffer type SF6 circuitbreakers at 7.2, 12 and 17.5 kV.tri1980.ElecBreakdown of interrupting techniques in theEEC' : MV circuit breakers1981Reliability confirmed with theinspection of the first circuit-breakersdelivered : no change in pressure,minimum erosion of arcing contacts.www198285 EEC : European Economic CommunityMost of the breakers manufactured byMerlin Gerin use the SF6 techniqueand performances progress rapidly : the Fluarc circuit breaker doubles itselectrical endurance, the Vercors M6 load break switchtriples its breaking capacity for highlyinductive currents, the Rollarc contactor doubles itsrated current and breaking capacity.90Further progress : the Fluarc circuit breaker rangeextended with the Fluarc FG3 andFG4, Merlin Gerin introduces the circuitbreaker in MV/LV transformersubstations : the RM6 ring main unit isnow available with an SF6 circuitbreaker specially adapted to theperformance requirements of MV/LVtransformer protection.1989Merlin Gerin remains at the forefront : the SFset, the first autonomous MVcircuit breaker with integrated digitalprotection ; the SFset is speciallydesigned for the protection of MV/LVtransformer substations, VIP 200, the first microprocessor based protection unit requiring noauxiliary power source, SF6 ring main units - over 50 000RM6 switch units throughout the world,confirming Merlin Gerin as worldleader, VM6 modular cubicles: the 200 000 thunit installed.

.coma breaking gasLike all gases in current use, SF6 isavailable in cylinders in all countries ofthe world. Among many applications,SF6 is used as a tracer gas forleakage tests in the petrochemical andnuclear industries. It is also used forvery diverse applications : electronmicroscopy, particle acceleration, etc.SF6 is non-toxic. The use of this gasin electrical switchgear assures thesafety of the personnel and theinstallations. Dozens of thousands ofSF6 switchgear units in servicethroughout the world have proved thisunder severe operating conditions.SF6 is "the" breaking gas, combiningthe most properties : high capacity for carrying the heatproduced by the arc. The latter isstrongly cooled by convection duringarcing. high radial thermal conduction andhigh electron capturing capacity. Whenthe current passes through zero, thearc is extinguished by the combinationof these two phenomena :c SF6 permits rapid heat exchangefrom the centre of the arc towards theexterior,o fluorine atoms, which are highlyelectro-negative, act as veritable"traps" for electrons.Since it is the electrons which aremainly responsible for electricconduction in the gas, the gapbetween the contacts recovers itsinitial dielectric strength through thiselectron capture phenomenon atcurrent zero. the decomposition of the SF6molecule is reversible. The same massof gas is therefore always available,making the device self-sustainedthroughout its operating life.anFa widely available gasualsthe switchgearmanufacturers' gasa non-inflammable gastMSF6 is an inert gas and does notsustain combustion.Fa very stable gasSF6:sulphur hexafluoridearThe high stability of the SF6 gas isdue to the 6 covalent bonds of itsmolecule.calPan insulating gaslectriThe dielectric strength of SF6 issuperior to that of most known media,reaching 5 times that of air at apressure of a few bars.Eenthalpy (103J/g)thermal conductivity50Q05(W em ' K ')Q04Q03Q02www0,01246810 12temperature (10' K)At high temperature, thedecomposition of the SF6molecule is reversible,therefore the gas does notwear down.051015temperature (1 0' K)One gramme of SF6 cancarry 30,000Joules at 12,000 K(breaking at 25 kA)temperature (10' K)The arc is surrounded by acolumn of hot gas, extremelyeffective in carrying away theheat (thermal conductivitypeak at 2000 K) withoutconducting the electriccurrent.

.comualsto remove the heat produced by the electric arc, relativemovement must be created between the arc and the SF6gas or the heat produced by the arc must be used tocreate a pressure difference.allows scopefor a varietyof techniquesTwo solutions are possible : displacing the gas by forcedconvection (puffer technique), displacing the arc by magneticblowout (rotating arc technique).puffer techniquetManSimplicityThe arcing contacts, when theyseparate, drive a piston. The SF6 thuscompressed is channelled by aninsulating nozzle between the arcingcontacts. These contacts are tubularand can evacuate the hot gas throughtheir interior by forced convection.Longer lifeWear on the arcing contacts is verylow on account of the instability of theroots of the arc inside the tubularcontacts.rotating arc techniqueA sound methodRotation of the arc between thecircular arcing contacts is caused byan intense electromagnetic field. Thisfield is produced by a solenoid throughwhich the current to be interruptedflows at the moment of opening.EfficiencyThe power required to blow out the arcis supplied by the system. Control isthus simple and economical.Longer lifeThe rapid movement of the arc rootsover the contacts substantially limitserosion of the contacts.Forced injection of a small quantity of cold gas(breaking of a low current)www.ElectricalParEfficiencyHalf a litre of gas is sufficient forbreaking. With this technique, low loadcurrents can be interrupted asefficiently as heavy currents even at50 kA, as the natural auto-expansionof hot gasses towards the colder areasof the bottle result in a rapiddissipation of the gas.Clogging effectWhen breaking heavy currents, the arcoccupies the whole of the spaceavailable between the arcing contacts.Gas flow is thus impeded : this is theclogging effect. This naturalphenomenon has two beneficialresults: storage, before the current passesthrough zero, of almost all the gascompressed by the piston, arcing energy limited by the brakingof the moving parts, which limits thelength of the arc.Natural thermal expansion effect downstream ofthe tubular contacts (breaking of heavy currents)Rotating arc technique

.com1The mechanical andelectrical endurance of SF6switchgear is far above thatrecommended by the IEC.Its life is estimated at a minimum of 20years even on systems where theswitchgear is very much in demand.This level of performal'l ce isparticularly appreciated in publicdistribution substations.at least 20 years lifedecisiveadvantages2ualszero maintenance3sealed-for-life bottles45simple technologySF6 switchgear requiresneither inspection nor specialmaintenance : the gas does not weardown as molecule decomposition isreversible ; wear on arcing contacts is veryslight; the operating mechanism needslittle or no maintenance depending onits use.aninsensitive to theenvironmenttM6smooth breaking technique :no overvoltages78arswitchgear to meetindividual requirements9lPcompetitive technology,economy-wisecaconfirmed experienceThe moving parts ofcontactors, breakers andswitches are enclosed in asealed-for-life bottle (type 3 IEC). A rotary system assurestightness around movementtransmission shaft.10www.Electritechnique of the futureThe switchgear is designedwith the key parts inside thissealed vessel, the fullassembly constituting a totalinsulation system.This sealed design makes theswitchgear totally insensitive to theenvironment (pollution, weather, etc.).

Experience based on400,000 SF6 switchgearunits: 100,000 Fluarc circuitbreakers since 1971 , 300,000 load break switches since1975.Installed the world over, this apparatusis tested daily and the confidenceshown by the users is fully justified.catri.Elecwww.comualstManSimple design, universalparts and materials, testedproduction and inspectionprocesses. . . ,the reasons behind the lowmanufacturing costs of SF6switchgear. Prices are sure to remaincompetitive.lPWith puffer or rotating arctype SF6 switchgear, there isno need for any device toreduce switching surges.This feature is particularly useful forthe control of motors, as theirinsulation levels are much lower thanthose of the rest of the circuit.Current chopping is perhaps the bestknown phenomenon, but it is not themost dangerous for a motor. Thesurges produced by successive re ignitions on opening or successive pre strikes on closing are much moreharmful, due either to the amplitude ofthe overvoltage or to its rate of rise.These surges are likely to take placein vacuum circuit-breakers having anextremely high rate of rise of dielectricrecovery. They do not occur in SF6switchgear.This is particularly of interest forcontactors.The Rollarc contactor can be usedwhatever the rating of the motors, theirmethod of starting, the length of theleads, and so forth. This contactor alsohas a very high breaking capacitywhich is essential to achieve a properfuse-contactor combination for motorprotection.To meet all installationrequirements, SF6switchgear offers manysolutions : single or three-pole housing ; fixed or withdrawable switchgear , compact apparatus ; indoor or outdoor equipment, fullyinsensitive to the environment.arThe technology implementedby SF6 switchgear istemptingly simple : unsophisticated contactswith customary alloys ; strong moulded resin or metalcasings.Their design allows optimization ofform (complete poles, three-polecasings or enclosures).This simplicity also facilitatestechnology transfer for localmanufacture of switchgear units.The SF6 breaking techniqueallows the design to developalong several lines whichhave not all yet beenexplored.The considerable evolutionary potentialis one with propects for the future.