A STUDYOF THEEFFECTOF AGINGON THE OPERATIONOF SWITCHINGDEVICES

An experimental studywas conducted jectedto the stressesof an accident,duringwhich to determinewhetherequipmentagingaffectsthe the equipmentis requiredto performa safety vulnerability of electricswitching devicesto mal- function.The studyreportedhereinwas an effort functioncausedby vibratory stressesin the range to determine experimentally theeffectofaccelerated of seismicfrequencies and accelerationamplitudes. aging on the vulnerability of electricswitching The studyincludeda vibrationtestbeforeandafter devicestomalfunction as a consequenceof a seismic a programof acceleratedagingdesigned to simulate disturbance. Whilethe acceleratedaging program fortyyearsof servicein areasoutsidethecontain- was intendedto be typicalof programsusedin the ment of a nuclearpowergenerating station.Gamma qualification of electrical switchingdevices,its irradiation,thermal aging,electrical/mechanical correlation with a specificset of servicecondi- cyclingand simulationof operatingbasisearth- tionswasnotofmajorimportance. quakeswere includedin the programof accelerated aging.Malfunction was definedas spuriousopening TESTSPECIMENS or closingof contactsfortimesin excessof 1 ms duringthevibration tests. Thisprogramwas conductedon the 24 specimens listedinTable1. Specimens 1B through18Bconsti- For most devicesthe fragilitylevelwas ap- tute a seriesof 9 pairsof duplicatespecimens; proximately the same beforeand afteraging. In specimens 27Band 28B,whichareidenticalto speci- some cases the fragilitylevel increased and in mens 7B and 8B,were addedto the programafter the othersit decreased, but the changeswere usually initialseriesofvibration testshadbeencompleted. not significantly differentfrom the differenceof fragility levelsobservedfor duplicatespecimens Table1. Identification ofTestSpecimens under identicaltest conditions.Because of the absenceof a clearcorrelation betweenaccelerated Note:Allspecimens consisted ofduplicate pairs, , ~~~~~~~~~except specimens 19Bthrough22B agingand the vulnerability to vibratory stresses, exceptspecimens_19B_through_22B the resultsof thestudydo not supporttherequire- ment that seismicqualification be conductedwith