Download - Schneider Electric

More documents

Recommendations

Info

In Francev On EHV networks (400 and 225 kV), variousreclosers are used:- slow single-phase reclosers tripping in eventof single-phase faults: breaking time is around1.5 to 2 s,- slow three-phase reclosers (multiphase faults),whose operation depends on voltagesynchronisation check: breaking time is around5 s. These reclosers are also used onHV networks (90 and 63 kV).v On overhead MV networks (5 to 20 kV) forwhich the neutral is earthed by an impedancelimiting the earth fault current to 300 A in theprimary substation, “shunt circuit-breakers”eliminate intermittent single-phase faults(contacts with branches) without affectingLV users (see fig. 3 ).However, multiphase faults are treated by rapidand slow reclosers that cause voltage dips onLV (see fig. 4 ). Roughly 75% of faults areeliminated after rapid reclosing that correspondsto the conventional short 300 ms interruption.v On underground MV networks (5 to 20 kV).In theory there are no intermittent faults, thus allfaults result in “permanent” de-energisation ofthe faulty part of the network. Consequentlyunderground networks (town) are organisedeither in “double shunt” (see fig. 5 ) or, in mostcases, in an open ring (see fig. 6 ).Automated systems restore supply to fault-freeHV/LV substations in less than one minute.N300 A Shuntcircuit-beakerFig. 3 : elimination of a single-phase fault by a shuntcircuit-breaker which short-circuits the fault, thusquenching the arc.a - Current inrush by the faulty feederIn0t (s)HVb - Voltage on the faulty feederMVUn0∆ut (s)Faulty feederc - Voltage on the other feedersUn0∆ut (s)Originof fault0.1 0.3 0.5 150.5 PermanentRapidreclosingSlowreclosingCircuit-breakeropeningCircuit-breakeropeningCircuit-breakeropeningPrinciple: On an overhead MV network, most faults are intermittent. Thus, the incoming circuit-breaker oneach feeder is equipped with an automated system that attempts two reclosings (sometimes three):c the first instantaneously (opening + closing time: 0.3 s),c the second after roughly 15 s.Fig. 4 : voltage fluctuations on rapid and slow reclosing on a MV distribution network.Cahier Technique Schneider Electric no. 141 / p.6
HV/MVsubstationHV/MVsubstationCircuit “A”Circuit “B”UIncomer“A”Incomer“B”Networksuppliedby…101010AtfBtfAtf = 5 or 25 stFig. 5 : double shunt MV power supply. In the box, automated system sequence for a Merlin Gerin changeoverswitch conform to EDF specifications (France).HV/MV transformersHV/MVsubstationSupply path of all substations except no. 1Supply path ofsubstation no. 1MV/LVtransformersMV/LVtransformersSubstation no. 1Ring openingpointMV/LVtransformersFig. 6 : open ring MV power supply (main feeder interruption).Cahier Technique Schneider Electric no. 141 / p.7
Page 1 and 2: Collection Technique ..............
Page 3 and 4: no. 141Electrical disturbances in L
Page 6 and 7: 1 LV industrial voltagesAll network
Page 10 and 11: Disturbances due to operation ofLV
Page 12 and 13: LightningLightning directly affects
Page 14 and 15: Switchgear operations and operation
Page 16 and 17: FerroresonanceThis phenomenon may o
Page 18 and 19: 3 Sine wave disturbancesVoltages (w
Page 20 and 21: Standard EN 50160 indicates, for pu
Page 22 and 23: 4.2 Phase unbalanceBesides the effe
Page 24 and 25: There is a large diversity of radia
Page 26 and 27: Appendix 1: transmission of overvol
Page 28 and 29: BibliographyStandardsc EN 50160: Vo
Page 31: Schneider ElectricDirection Scienti

Download - Schneider Electric

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?