IEC_60466-198720Parte5.pdf

IeC 4b6 7484489100438722466IEC198771APPENDIX AAINTERNAL FAULTTABLE AAILaocations,causes and examples of measures decreasing the probabilityof internal faults or reducing the riskLocations whereinternal faults arePossible causesmore likely to occurof internal faultsExamples of measures(1)(2)(3)Cable boxesInadequate designSelectiou of adequate dimensions.Faulty installationAvoidance of crossed cable connections.Checkingof workmanshtip on site.Failure of solid or liquid insu-Checking of workmanship and/or dielectric test onlation(defective or missing)site.Regular checking of liquid levels.DisconnectorsMal-operationInterlocks(see Sub-clause 5.106).Delayed reopeningSwitchesIndependent manual operation.Short-circuit mak-Earthing switchesing capacity for switches and earthing switches.Instructions to personnel.Bolted connectionsCorrosionUse of corrosion inhibiting coatings and/or greases.and contactsEncapsulation,where possible.Faulty assemblyChecking of workmanship by suitable means.Instrument trans-FerroresonanceAvoidance of these electrical influences by suitableformersdesign of the circuit.Circuit-breakersInsufficient maintenanceRegular programmed maintenance.Instructions topersonnel.All locationsError by personnelInsulation-embedded live parts.Instructions to per-sonnel.Ageing under electric stressesPartial discharge routine tests.Pollution,moisture,ingress ofMeasures to ensure that the specified service con-dust,vermin,etc.ditions are met(see Clause 2).OvervoltagesLighuning protection.Adequate insulation co-ordi-nation.Dielectric tests on site.TABLE AAIIExamples of measures.limiting the consequences of internal faults-Rapid fault clearance times initiated by detectors sensitive to light,pressure or heat or by a differentialbusbar protection-Application of suitable fuses in combination with switching devices to limit the fault current and faultduration-Remote control-Pressure relief flapsCopyright por International Electrotechnical CommissionMon Jun 16 16:42:23 2003IEC 46b 87484489100438746466IEC 1987-73-METHOD FOR TESTING THE ENCLOSED SWITCHGEAR AND CONTROLGEARUNDER CONDITIONS OF ARCING DUE TO INTERNAL FAULTAA1.IntroductionThe occurrence of arcs inside enclosed switchgear and controlgear is coupled withvarious physical phenomena.For example,the arc energy resulting from an arc developed in air at atmospheric.pressure will cause an internal overpressure and local overheating,which will result inmechanical and thermal stressing of the equipment.Moreover,the materials involved mayproduce hot decomposition products,either gaseous or vaporous,which may bedischarged to the outside of the enclosure.This standard makes allowance for internal overpressure acting on covers,doors,inspection windows,etc.,and also takes into consideration the thermal effects of the arcor its roots on the enclosure and of ejected hot gases and glowing particles,but notdamage to partitions and shutters.Consequently,it does not cover all effects which mayconstitute a risk,such as toxic gases.Moreover,the test procedure only simulatessituations when doors and covers are closed and correctly secured.AA2.Types of accessibilityA distinction is made between the two types of accessibility corresponding to thedifferent test conditions given in Sub-clauses AA5.3.2 and AA5.3.3.The enclosure mayhave different types of accessibility on its various sides.Type A:Enclosed switchgear and controlgear with accessibility restricted to authorizedpersonnel only.Type B:Enclosed switchgear and controlgear with unrestricted accessibility,including bythe general public.AA3.Test arrangementThe choice of the functional units,their number,their equipment and their position inthe room,as well as the place of initiation of the arcare to be decided upon inconsultation.In each case,the following points shall be observed:-the test should be carried out on a functional unit not previously subjected to arcing;-the crection conditions should be as close as possible to those of normal service.Theroom should be represented at least by the floor,the ceiling,two.perpendicular wallsand the cable ducts;Copyright por International Electrotechnical CommissionMon Jun 16 16:42:27 2003404474-74-466.CEI 1987-Iunit fonctionnelle devra tre compltement quipe.Il est permis dutiliser deselements de remplacement de materiels interieurs a condition queleur volume et lamatiere de leur partie externe soient identiques a ceux de loriginal;-Iunite a essayer est mise a la terre a lendroit prevu;-Iamorcage darc ne se fait pas dans des conditions ne correspondant pas aux conditionsde service.AA4.Courant et tension appliquesAA4.1 GeneralitesDans Iappareillage sous enveloppe,il convient deffectuer les essais en triphasc.Lccourant de court-circuit appliqu pendant Iessai doit etre spcifi par le constructeur.Cette valeur peut tre gale ou infrieure aucourant de courte dure assign.AA4.2 TensionLa tension applique sur le circuit dessai est on principc gale la tension assigncde lappareillage sous enveloppe.Une tension inferieure a cette valeur peut tre choisie siles conditions suivantes sont respectees:a)le courant reste pratiquement sinusordal;b)-1arc ne seteint pas prematurement.AA4.3 CourantAA4.3.1 Composante alternativeLe courant de court-circuit spcifi pour le cas damorcage darc dans lappareillagesous enveloppe est en principe rgl avec une tolrance de.+5%et 0%.Ces tolrancessappliquent au courant presum seulement si la tension appliquee est gale a la tensionassignee.Le courant reste en principe constant.Note.-Si la station dessai ne permet pas cela,la dure dessai sera allongle jusquau moment od Iintgrale deia composante alternative du courant devient gale a la valeur specifiee avec une tolerance de+10%et0%.Dans ce cas,le courant est en principe gal a la valeur spcifiee au moins pendant les troispremieres demi-priodes et ne descend pas en dessous de 50%de la valeur spcifie a la fin de lessai.AA4.3.2 Composante aperiodiqueLe moment de la fermeture est en principe choisi de telle fayon que la valeur de cretedu courant prsum(avec une tolrance de+5%et 0%)parcourant.une des phasesextremes soit 2,5 fois la valeur efficace de la composante alternative dfinie auparagraphe AA4.3.1 et quune grande boucle de courant soit simultanment prsente danslautre phase extrme.Si la tension est infrieure a la tension assigne,la.valeur de crtedu courant de court-circuit pour lappareillage sous enveloppe en essai nest en principepas infrieure a 90%de la valeur de crete prsume.AA4.4 FreguencePour une frquence assigne de 50 Hz ou 60 Hz,la frquence au dbut de lessai sesitue entre 48 Hz et 62 Hz.Pour dautres frquences,la variation par rapport a la valeurassignee nexcede pas 10%.Copyright por International Electrotechnical CommissionWon Jun 16 16:42:29 2003