Chap.7Circuit-InterruptingDevicesPart1TypesNotes1.Circuit-interruptingdevicesinpowersystemsareofmanyforms,rangingfromthesmallkeyswitchestotheenormouscircuitbreakersthatcontroltheflowofpowerinhigh-voltagenetworks.

2.Threebasictypesofcircuit-interruptingdevicesarerecognized.1)Aswitchisadeviceformaking,breaking,orchangingtheconnectionsinanelectriccircuit.Thisdefinitionimpliesthattheswitchisusedinasysteminitsnormaloperatingcondition.Chap.7Circuit-InterruptingDevices

Chap.7Circuit-InterruptingDevices2)Acircuitbreakerisadeviceforinterruptingacircuitbetweenseparablecontactsundernormalorabnormalconditions. Theabnormalconditionsduringwhichacircuitbreakermaybeaskedtooperateareprimarilythosewhichexistduringshortcircuits.

Chap.7Circuit-InterruptingDevices3)Afuseisanovercurrentprotectivedevicewithacircuit-openingfusiblememberdirectlyheatedanddestroyedbythepassageofovercurrentthroughit. Fusesareusedinmanyapplicationsondistributionprimarycircuitsandtoalimitedextentonbulkpowerhigh-voltageequipment.

Chap.7Circuit-InterruptingDevices3.Inbreakersforoperationinlow-voltageaccircuits,advantagesistakenofthevoltagerequiredtoestablishacathodespot.

Chap.7Circuit-InterruptingDevicesPart2AirCircuitBreakerNotes1.Thelongerarcisreadilycooledbyconvectionaircurrentsandbyradiation,andthelongerpositivecolumnrequiresahighervoltage.

Chap.7Circuit-InterruptingDevicesPart3OilCircuitBreakerNotes1.Aninsulatingchamberfilledwithoilsurroundstheclosedcontacts.2.Whenthemovingcontactislowered,thearcisdrawnoutthroughthethroatofinsulatingchamber.

Chap.7Circuit-InterruptingDevices3.Theportionofthearcwithinthechambergeneratesgaswhichforcesoiloutthroughthethroat,whereitisinintimatecontactwiththearctocoolit,encouragerecombination,andphysical