Calculation of the starting performance of solid pole synchronous motors by the time-stepping finite element method

Torque production in solid pole machines is largely dependent on the currents that are induced into the rotor pole faces during starting conditions. The problem of predicting the distribution of currents in the pole face is challenging due to the nonlinear magnetic behaviour of the pole material. For this reason, the problem of deriving appropriate equivalent circuit parameters that can be used in starting calculations can be much more challenging for solid pole machines than for laminated salient pole machines with dedicated cages. This paper will discuss the electromagnetic behaviour of solid pole machines during starting conditions with particular emphasis on starting currents, torques and pulsation torques. The time-stepping finite element method provides a very rigorous method of modeling the electromagnetic phenomenon during the machine acceleration but can be too time consuming to perform for routine design work. This paper describes a recent finite element study that was made, gives comparisons to actual factory tests and discusses the advantages and disadvantages of the method for use in routine design work.