Improving the induction motor starting mode under a voltage drop conditions

Asynchronous motors are the most common electric motors used to drive work machines. This is due to their high structural reliability and other significant advantages. During operation, they are exposed to a variety of operational influences. One of the most frequent of these is a voltage dip. As a result of this influence, the performance of the electric motor deteriorates both in steady-state and starting modes. A voltage drop is especially dangerous when starting an electric motor, as it leads to an increase in starting time and a decrease in starting torque. The thermal effect of inrush currents during a voltage dip can lead to motor failure. Therefore, the article proposes to increase the voltage in one of the phases of an induction motor during the startup period under conditions of voltage dip. To assess this technical impact, a methodology has been developed for studying the starting torque and starting time of an induction motor under conditions of rated voltage, voltage dip, and voltage asymmetry. It takes into account the voltage reduction factor, the voltage ratios of the forward and reverse sequences, and the motor load factor. The evaluation criteria are the starting torque of the motor and its starting time. The paper compares these criteria according to the developed methodology in the following cases: nominal mains voltage, mains voltage dip, mains voltage dip with an artificial increase in voltage in one of the induction motor phases. The results of the comparison in these cases showed the effectiveness of artificial voltage asymmetry for the period of starting the motor during a voltage dip. To implement the proposed idea, a block diagram of a device for improving the starting mode of an induction motor under voltage dip conditions was drawn up.