Abstract
| In this paper there are analyzed a series of dynamic regimes that occur in the case when a phase of an asynchronous motor is accidentally interrupted and in the case when the resistant torque increases by step. For these situations there have been carried out, starting from the motor equations written in the two-axes theory, two Simulink programs (detailed in the paper). With their help, for a motor rated at1,2 kW, there have been obtained relevant simulations together with conclusions emerging from them. Thus, in the case when a phase was interrupted it results that: the interruption of a phase leads to a dynamic regime that is relatively quickly stabilized; this stabilized regime is characterized by high values of currents, slight decrease of the rotor speed, small oscillations of speed, important oscillations of torque. In the case when the resistant torque is modified by step there have been resulted the following conclusions: a reduced torque shock leads to increased values of the currents and to a slight decrease of the speed (after a few oscillations); an increased value of the inertia moment leads to an increased number of current oscillations in dynamic regime but also to the disappearance of the speed and torque oscillations when a torque shock occurs; for very high resistant torques the maximum torque developed by the motor becomes smaller than the resistant one which causes the decrease of the speed towards zero, finally reaching, if the protections do not cut, the shortcircuit regime; the simulation program conceived here can also be used for establishing the value of the motor maximum torque; the simulations have been confirmed, as essential elements, quantitatively and qualitatively, by experiment. |
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