PRINCIPAIS PONTOS NORMAS TRANSFORMADORES SECOIEEE C57.12.01-1989 (trecho citado no item 7.2 da norma IEEE C57.12.91-1995)9. Tolerances 9.1 Ratio. ith rated !olta"e im#ressed on one $indin" o% a trans%ormer& all other rated !olta"es at no load shall 'e correct $ithin 0&5( o% the name #late mar)in"s. Rated ta# !olta"es shall corres#ond to the !olta"e o% the nearest t*rn i% the !olta"e #er t*rn e+ceeds 0&5( o% the desired !olta"e.9.2 Im#edance. The tolerances %or im#edance shall 'e as %ollo$s,(1) The im#edance o% a t$o-$indin" trans%ormer shall ha!e a tolerance o% -.- 7&5( o% the s#eci/ed !al*e. 0i1erences o% im#edance 'et$een t$o d*#licate t$o-$indin" trans%ormers& $hen t$o or more *nits o% a "i!en ratin" are #rod*ced '2 one man*%act*rer at the same time& shall not e+ceed7&5( o% the s#eci/ed !al*e.(2) The im#edance o% trans%ormers ha!in" three or more $indin"s or ha!in" three or more $indin"s or ha!in" 3i"3a" $indin"s shall ha!e a tolerance o% -.-10( o% the s#eci/ed !al*e. 0i1erences o% im#edance 'et$een d*#licate three-$indin" or 3i"3a" trans%ormers& $hen t$o or more *nits o% a "i!en ratin" are #rod*ced '2 one man*%act*rer at the same time& shall not e+ceed10( o% the s#eci/ed !al*e.(4) The im#edance o% an a*totrans%ormer shall ha!e a tolerance o% -.-10( o% the s#eci/ed !al*e. 0i1erences o% im#edance 'et$een d*#licate a*totrans%ormer& $hen t$o or more *nits o% a "i!en ratin" are #rod*ced '2 one man*%act*rer at the same time& shall not e+ceed 10( o% the s#eci/ed !al*e.(5) Trans%ormers shall 'e considered s*ita'le %or o#eration in #arallel i% their resistance and reactances come $ithin the limitations o% 9.2 (1) thro*"h 9.2 (4)& #ro!ided t*rn ratios and other controllin" characteristics are s*ita'le %or s*ch o#eration.9.4 6osses. the losses re#resented '2 testin" a trans%ormer& or trans%ormers&on a "i!en order shall not e+ceed the s#eci/ed losses '2 more than the #ercenta"es "i!en in Ta'le 8.IEEE C57.12.91-1995...10.9 Ins*lation-resistance testsIns*lation-resistance tests are made to determine the ins*lation resistance %rom indi!id*al $indin"s to "ro*nd& or 'et$een indi!id*al $indin"s. The ins*lation resistance in s*ch tests is commonl2 meas*red in me"ohms '*t ma2 'e calc*lated %rom meas*rements o% a##lied !olta"e and lea)a"e c*rrent.Ins*lation-resistance tests shall 'e made $hen s#eci/ed. The ins*lation resistance o% electrical a##arat*s is o% do*'t%*l si"ni/cance as com#ared $ith the dielectric stren"th. It is s*'7ect to $ide !ariation $ith desi"n& tem#erat*re& dr2ness& and cleanliness o% the #arts. hen the ins*lation resistance %alls 'elo$ #rescri'ed !al*es& it can& in most cases& i% it is o% "ood desi"n and has no de%ect& 'e 'ro*"ht *# to the #rescri'ed !al*e '2 cleanin"and dr2in" the a##arat*s. The ins*lation resistance& there%ore& ma2 a1ord a *se%*l indication as to $hether the a##arat*s is in s*ita'le condition %or a##lication o% the dielectric test.89TE:,1 ; The si"ni/cance o% !al*es o% ins*lation-resistance tests "enerall2 rell $indin"s short-circ*itedc) >ll '*shin"s or terminals in #laced) Trans%ormer tem#erat*re a##ro+imatel2 20 ?C10.9.2 Instr*mentationIns*lation resistance ma2 'e meas*red *sin" either o% the %ollo$in",a) > !aria'le-!olta"e dc #o$er s*##l2 $ith means to meas*re !olta"e and c*rrent ("enerall2 in micro-am#eres or milliam#eres)') > me"ohmmeter 89TE ; @e"ohmmeter are commonl2 a!aila'le $ith nominal !olta"es o% 500 A& 1000 A& and 2500 A. 0C a##lied test ell connections shall ma)e"ood mechanical 7oints $itho*t %ormin" shar# corners or #oints. :mall 'are $ire ma2 'e *sed in connectin" the res#ecti!e ta#s and line terminals to"ether& '*t care shall 'e ta)en to )ee# the $ire on the hi"h-!olta"e side $ell a$a2 %rom the "ro*nd. 8o a##recia'le resistance sho*ld 'e #laced 'et$een the testin" trans%ormer and the one *nder test. It is #ermissi'le& ho$e!er& to *se reacti!e coils at or near the terminals o% the testin" trans%ormer. > relie% "a# set at a !olta"e 10( or more in e+cess o% the s#eci/ed test !olta"e ma2 'e connected d*rin" the a##lied-!olta"e test.10.4.5 Aolta"e rate o% riseThe !olta"e sho*ld 'e started at one-%ter 'ein" held %or the time s#eci/ed& it sho*ld 'e red*ced "rad*all2 (in not more than 5 s) to one