SUSCEPTIBILITY OFflISTRIBUTION TRANSFORMERS TOLOW-VOLTAGE SIDtLIGHTNING SURGEFAILURE
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Thesusceptibility of commondesignsof experimenton a ruraldistribution systemin the single-phase overheaddistribution transformers to 1940's,the application of arrestersto the low- failurecausedby lightning currentsurgesentering voltageterminals reducedtransformer failure ratesto the transformer via the normallyunprotected low- one-fourth therateof transformers withoutthear- voltageterminals has beeninvestigated. Evidence resters.Thesamereference revealed thatdiffering fromexamination of transformers thathavefailedin transformer designsandlow-voltage coilconnections service,transient analysismeasurements of'scaled havediffering responses tothelow-side surges,but surgesapplied tothehigh-andlow-voltage windings, itdidnotidentify thedesigns.Alsonoted wasthat anda full-scale currentsurgeimpulse test,indicate arrestersprotectingthe high-voltage coilswere thattheshell-type designsut'ilizing a non-interlacedineffective in protecting the transformer fromthe 120/240-volt ratingaremostsusceptible to'failure. low-side surges,althoughfailures generally occurred Shell-typeand core-typedesignswith interlaced withinthehigh-voltage winding. low-voltage windingsareleastsusceptible. Suscep- Despitethe findingsin theseReferences, the tibility isinversely relatedto kVArating,ormore application ofarrester protection at thelow-voltage specifically, to thevoltsperturnemployedbythe terminalsof distribution transformers hasnotbeen designer.Withthe increasing trendto lowercore generally practiced byutilities inNorthAmerica.It losstransformers, reducingthevoltsperturnwill canbe inferred thatthefailurerateof susceptible increase thishazardonnoninterlaced windings. designswasnotexcessive, orthatmostdistribution transformers useddesignsthatwerenotsusceptible to failure.However,sincethe1960's, therehavebeen