Critical Analysis of Commercial Power Main Transient Designs

T h ere a re tw o co m m o n v iew poin ts f o r t r a n s ie n ts on low vo ltag e (less th a n 1000 vo l ts RMS) pow er m ains . Many sys tem designers b e liev e t h a t h a rm fu l pow er m ain t r an s ie n ts to n o t ex is t as th e non-consp icuous t r a n s ie n t s a re so t im e d e p en d en t th e y a re avo idab le . T hese sy s te m designers b lam e equ ipm en t m a lfu n c tio n s on som e o th e r reason . The o th e r v iew p o in t is f ro m th e r e s e a r c h e r s in E l e c t r o m a g n e t i c C o m p a t ib i l i ty (EMC) f ie ld who be lieve th e re a re h a rm fu l pow er m ain t r a n s ie n t s bu t choose l im its and a t e s t p ro ced u re based upon p a s t ex p e r ien c e no t analysis . T h ere is som e basis fo r b o th v iew po in ts . Today, n ear ly all sy s tem s c o n ta in low pow er y e t high speed se q u e n tia l d ig i ta l logic. A m yriad of eq u ip m en t bes ides c o m p u te rs use p rocesso rs w ith som e form of a m em ory . Thus, a single, p roperly t im e d t r a n s ie n t can c r e a te se r io u s and s o m e t im e s n o n r e c o v e r a b le p ro b lem s when se q u e n tia l c i r c u i ts a re fa lse t r ig g e re d or ch ange logic s t a te . Som e sy s tem s a re in sensis tive to a single t ra n s ie n t due to an a u to m a t ic r e co v e ry f e a tu r e bu t fa il when m ultip le t r a n s ie n t s occu r . One of th e m ost puzzling q u est io n s th e EMC d e s ig n e r s is t h e a m p l i t u d e o f t h e im p u ls e t e s t . M easured pow erm ain c o n d u c ted t r a n s ie n t t e s t in g has proven t h a t fo r any c o m m e rc ia l co s t c o m p e t i t iv e eq u ipm en t, th e re is som e lev e l of t r a n s ie n t s a t which th e eq u ip m en t has som e d e g re e of su sce p t ib i l i ty and th e r e is som e h igher lev e l which will a lw ays m ake th e equ ipm en t fa i l [1]. F o r e x am p le , F igure 1 shows th e m easu red peak am p li tu d e req u ire d fo r a pro d u c t to fa i l . Below 50 v o l ts , no f a i lu r e s o c c u r re d , w h ereas in th e 500 to 2000 volt ra n g e th e p roduc t has 100% fa ilu re . The basic q u est ion is, w h a t is an a c c e p ta b le value? The an sw er is, th e re is no m agic value , only a c o s t e f f e c t iv e design which m ust use d i f f e re n t d a ta and m odel fo r each type of t r a n s ie n t . A lthough n o rm al t e s t eq u ip m en t such as scopes can m easu re line t ra n s ie n ts , sp ec ia l t e s t se tu p s a re requ ired to d e te rm in e th e t ru e sy s tem su sce p t ib i l i ty levels. B ecause o f th e la rg e num ber of co m p an ies worldwide in the pow er m ain t r a n s ie n t p ro te c t io n business, f ie r c e c o m p e t i t io n has c r e a te d h y p e rad v e r t i se m en ts . One must d e te rm in e the t e c h n ic a l i ssues and so lu t io n s v e rsu s f a ls e o r u n n eed ed re q u ire m en ts . F o r exam ple , is subnanosecond p r o t e c t io n response re q u ire d fo r pow er mains t ra n s ie n ts? T he an sw er is no, un less EMP p ro te c t io n is w anted . Power Mains Susceptibility