KYORITSU 6050 - RCD TESTS

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6.1PrinciplesofMeasurement
TheRCDtesterisconnectedbetweenphaseandprotectiveconnectors
on the load side of the RCD after disconnecting the load. A precisely
measuredcurrentforacarefullytimedperiodisdrawnfromthephase
andreturnsviatheearth,thustrippingthedevice.Theinstrument
measuresanddisplaystheexacttimetakenforthecircuittobeopened.
AnRCDisaswitchingdevicedesignedforbreakingcurrentswhenthe
residualcurrentattainsaspecificvalue.Itworksonthebasisofcurrent
differencebetweenphasecurrentsflowingtodifferentloadsand
returningcurrentflowingthroughtheneutralconductor(forasingle-
phaseinstallation). Inthe case where the current difference is higher
thanthe RCD tripping current, the device will trip and disconnectthe
supplyfromthecurrent.
TherearetwoclassificationsforRCDs;thefirstoneduetotheshapeof
theresidualcurrentwaveform(typesACandA)andtheseconddueto
thetrippingtime(typesGandS).
● RCDtypeACwilltripwhenpresentedwithresidualsinusoidal
alternating currents whether applied suddenly or slowly rising. This
typeisthemostfrequentlyusedonelectricalinstallations.
● RCDtypeAwilltripwhenpresentedwithresidualsinusoidal
alternatingcurrents(similartotypeAC)andresidualpulsatingdirect
currents(DC)whethersuddenlyappliedorslowlyrising.Thistypeof
RCD is not commonly used at present, however, it is increasing in
popularityandisrequiredbythelocalregulationsinsomecountries.
● RCDtypeG.InthiscaseGstandsforgeneraltype(withouttrip-out
timedelay)andisforgeneraluseandapplications.
● RCDtypeSwhereSstandsforselectivetype(withtrip-outtime
delay).ThistypeofRCDisspecificallydesignedforinstallations
wheretheselectivity characteristic isrequired.Inordertoassure
successfulprotection on an electrical installation using RCD's they
shouldbecheckedtotesttrip-outtimet⊿.
● Trip-outtime t⊿ isthetime needed bythe RCDto trip at a rated
residualoperatingcurrentof I⊿n. The standardvaluesoftripping
timearedefinedbyIEC61009(EN61009)andIEC61008(EN
61008)andarelistedinthetablebelowforI⊿nand5I⊿n.
6.RCDTESTS