Numerical Modeling and Simulation of Unsymmetrical Transients on Synchronous Machines With Neutral Included

The synchronous-machine models presented in the literature often depend on the applications contemplated by their authors. Various particular points in the machine's behavior such as arbitrary number of dampers, the Canay reactance in the d-axis and zero-sequence axis, have been presented by different authors. In general, for several applications and, in particular for time-domain parameter identification, only linear models with constant rotor speed and symmetrical transients tests are used. These models are not appropriate for the analysis of unbalanced transients with speed variation. What we propose in this paper, with a simple albeit general mathematical formulation, is an improved synchronous-machine model. The improvement is achieved by including the neutral of the machine, the Canay reactance in both d and q axes and the zero-sequence component of Park's reference frame into known models. Using this complete model, we develop a simple and appropriate method for numerical modeling of both symmetrical and unsymmetrical transients of synchronous motors and alternators. As applications, all short-circuits at the machine terminals are presented and simulated using a turbine-machine model with three equivalent damper windings per axis.