This paper is, in part, an extended discussion of a paper by Atarod et al., presented at the 1992 IEEE/PES Winter Meeting. That paper raised some issues of modeling which require more extensive attention than is feasible in an ordinary discussion. In this paper, the author demonstrates that, regardless of the adequacy of second (one rotor damper branch) or third (two rotor damper branches) order models, a simple form for the rotor can be used. Physical reasoning was used by Atarod et al. to postulate the need for a "differential leakage" inductance element, representing flux linking both the field winding end damper bars but not the armature winding. The author employs circuit theory to demonstrate that this leakage element does not, by itself, contribute anything to the dynamics of rotor response, and that it is not required to adequately model the frequency response of rotor impedance. This means, that at least some of the conclusions of Atarod et al. are probably due to an artifact of the curve fitting technique used. Another curve fitting technique and its results are described.
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