The contribution of this paper is to propose an observability analysis for a nonlinear differential equations model describing a synchronous electrical drive. In the modern control systems the trend is to reduce the state variables to be measured and to estimate through an observer all variables which are needed. In this sense, an analysis of the observability of the model is always necessary. Throughout the paper a procedure for testing the observability is shown. Observability analysis allows to discover if the system is observable and in particular to discover those points or set in which the system is not observable. These points must be avoided from the observer and alternative procedure for the estimation of the state variable should be analyzed. The analysis of the presented drive model shows general results which can be extended to the family of such kinds of drives.