Abstract
The article presents formulas for calculating the static mechanical and electromechanical characteristics of an induction motor proceeding from its T-shaped equivalent circuit, and for the magnetization current, power at the motor terminals, and angle between the stator phase voltage and current as functions of the rotor speed. The presented formulas were used for analyzing and identifying three different power operation modes of the induction motor: a motor mode, a recuperative generator mode, and a generator mode with simultaneous power consumption from the network. The performed calculations made it possible to find the motor speeds at the ends of the induction motor’s mechanical characteristic part at which the motor operates in the recuperative generator mode. An analysis of calculation and experimental results was carried out, based on which the specific features of the recuperative mode of an induction motor fed from a frequency converter have been determined. It is shown that the range of parameters corresponding to the recuperative generator mode decreases with decreasing the supply voltage frequency. It has been found that the induction motor becomes unable to generate any amount of power to the supply network below a certain critical supply voltage frequency regardless of its running speed. A formula for the critical frequency has been derived. The calculated static characteristics for a 5.5 kW induction motor at the power supply frequencies equal to 50, 25, and 10 Hz, and for a 250 W motor at the power supply frequencies equal to 20 and 13 Hz are shown. The article also presents the experimental static characteristics of a 5.5 kW induction motor at the supply voltage frequencies equal to 40 and 20 Hz the location of generator modes in which is consistent with that found from the previous theoretical investigations.
Published Version
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