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In this paper, an inaccuracy of the method for induction motor parameter determination used in EMTP type simulation programs (ATP, EMTP96, EMTDC) is discussed. The paper presents a numerical method for the estimation of induction motor double-cage model parameters from standard manufacturer data, i.e., full load mechanical power (rated power), full load power factor, maximum torque, starting torque, starting current and full load efficiency. The nonlinear equations to obtain the motor parameters have been solved with a modified Newton method that always converges if the problem is well defined (that is, a solution exists). The method has been tested with 608 motors from different manufacturers. The manufacturer parameters that have a greater influence on convergence are the maximum torque and the starting current. The cases where the method does not converge have been studied and the range of variation of the maximum torque or starting current which determines where the data are well defined (that is, a solution exists) has been calculated.