Numerical estimation of equivalent circuit parameters of synchronous machines

Many aspects of electrical machine performance can now be very accurately assessed using numerical computation methods, usually, but not exclusively, finite element analysis. Before the advent of such numerical methods, and the computer hardware capable of supporting them, machine analysis involved the extensive use of equivalent circuits. A transitional era now exists between that of the analytical methods and that of the numerical methods. This era will probably be measured in decades rather than years, because the labour and computational effort involved in full 3-D transient numerical analysis are still considerable and threaten to remain so for some time yet. In the meantime, numerical techniques are routinely used for 2-D analysis of machine cross-sections and end-regions, and for 3-D studies of stator core features, end-rings, clamping plates etc. It is a positive aspect of the transitional era that numerical methods can be intelligently used to enhance as well as supplement traditional circuit techniques. Numerical analysis can be used to obtain accurate equivalent circuit parameters, especially where magnetic saturation and the effect of frequency on rotor impedance are significant. This paper presents a simple methodology for the calculation of two-axis equivalent circuit parameters for synchronous machines during asynchronous starting, based on 2-D finite element analysis.