Computer Model Analysis of Induction Motor Dynamic Contribution to Three-Phase Faults -- A Comparison with IEC909
Publication Date: 2012-May-07
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Computer Model Analysis of Induction Motor Dynamic Contribution to Three - Phase Faults - A Comparison With IEC 909
R D YOUSSEF('' and R E COSSE, Jr(')
I)M/lnnchestcrCcntre for Eiecuical Encrg, UMTS'L'. lJK ( 2 )The Ll W Kellogg ComFJiiy 1Iouston, I cus.USA
I'hz ak-iking dlfferericz between inductioii m dsynchronous ni:ichmes. insofar as their response to t:iults is concerned. is l'nc
itlc-rtiuci ol' machine excitation. A synchronuus maclunr obtains its cucitation honi a sepzratc dl: s m ~ ~ : :
which is \,irruallv
by the fault. Thus. as thc pnine niover contiiiiics to di-~vc
h esynchronous mactunc, excited at i t s pretault Ic\,cl. IC.
icspviids b! forcing large trnnsieni cumcnts (oward Uie fault. 'The induction machine, on die other hand, rscaves its escitatio:) l'rvin thc Ilric. if the line ~ ~ l t a g ~
drops, the m:ichine excitation is rcduced and its abilit). to drive the mechanical load is giutly iinpdired, hut because of tliz need for constant tlux Iiilhagcs. the machines restdual excitation u-ill furce decaying ac and uii:d:rcctional cui-rcnts into the fault for a fcw cycles.
In ths papcr. u modcl of rlic iiiduction mucor is prascntd a i d the machine dynamic :.espcnsc during a tlu.ee phase fault
:ii?.*iL!scd As!mmetl-y is addressed in the calculations kfandacturers niacll~neFsrarnrliers are used for study analyses of
ilitichi11ccontributions to tcmiinal faults. The computer gencratcd results arccoinpared w:lh the empirical IEC 909short-cii-cult calculation rnetIiodo10~to determine the magnitude of dBIEC309conservatism when rating clcchical mtci-rupting equjpineiii.
LV1it.n new elechicai sivitchgcar is installed in industrial l'xilitics there I S usually a considerable margin bctwccn tlic calcuiated fault magnitude andtlir maximum equipment rating capxbility. P!anning enginerrs incorporate future cmsiderations, such as increased utility short-circuit capabiIir]i., additional incoming utility-tie transformers and additional plant loads. Typically, plant expansions and
iiic~liricatioils rotating inductioii motor load< add tci the electrical disrribution systcin until thc fault contribution pushus tlie liniits uf the electrical apparatus. When this occurs, the hult cc1ritribu:ion may escccd the circuit bruakcr peak making ( v
iiitcn iiptiiig brcaking rating.
When updatcd E C909 short-circuit calculations indicaic t!iat the hult magnitudes are approximately h e same as the make and break ratings, detailed power system reviews occ~u. ' h esystem c o d p a t i o n is evaluated andthe system elements, par;imeters and quantities are chrckcd. This is obviously the niust fundlunental place to begin the review. At this point a critical philosophical decision must be rnadr'continuc to use I!-iC309 or use dyiamic calculations. Obviously. d>nainic calculations provide extwu+ refined results because cif the
precise dynamic inodcls used. Huwcvcr, \vhe IEC 909 [ I ,2] rrripirical calculation niet...