Experimental study of the process of the smooth starting asynchronous electric drive of turbo-mechanism with frequency converter

Asynchronous electric drive is widely used in agricultural production and is characterized by simplicity, reliability and low cost compared to other types of electric drives. Significant inrush currents during direct startup cause mechanical overloads in the working machine, which can be reduced with the help of frequency converters. In order to identify the patterns of change in the transient moment when starting the electric drive of the turbomechanism at different settings of the frequency converter, an experimental setup was used. It presents the dynamic moment when starting the electric drive that is measured by the displacement of the rotary platform using an elastic plate with a strain gauget, which resists rotation. The dynamic moment was measured using an analog input board with an ADC installed in a personal computer. To process the measurement results, specialized input board software, MS Excel and STATISTICA programs were used. It is revealed that the degree of reduction in mechanical overloads for an electric drive depends both on the choice of the pattern of change in the ratio of the voltage on the stator winding to the frequency, and on the acceleration time set in the frequency converter. The dependence of the maximum amplitude of the oscillation of the dynamic transient moment on the set acceleration time is exponential. It means that it is impossible to reduce mechanical overloads below a certain value, depending on the specific implementation of the frequency converter and the electric drive. There has been observed a maximum decrease in the amplitude of the oscillation of the dynamic moment by 10,2 times, which corresponds to the startup time set in the frequency converter of more than 0,4 s. It is considered appropriate for turbo mechanisms to use the pattern of changing the ratio of the voltage on the stator winding to the frequency, which has an initial section with a reduced gradient of voltage rise during the initial startup period, which makes it possible to "smooth out" electromagnetic transients in the electric motor at low voltage, while rapid acceleration occurs with a relatively small moment of resistance of the working machine.