Direct estimation of the generalised equivalent circuits of synchronous machines from short-circuit oscillographs

The calculation of equivalent circuits parameters from short-circuit time constants has been subject to a number of unnecessary assumptions and approximations. The authors describe and validate a procedure to circumvent this problem by estimating the equivalent circuit parameters directly from the oscillograph data. The synchronous machines´ models are generalised to include dampers in the direct and quadrature axes, thus providing a feasible approach for analysing short-circuit oscillographs when the machine is either a solid rotor turbogenerator or possesses a particularly complicated rotor geometry. Although the proposed least squares-based nonlinear strategy avoids all the various approximations necessary to relate the circuit parameters and the dynamic constants, it is shown that it does inherently lead to a suboptimal solution of the identification problem