Defining Acceptable Motor Reduction in Variable-Speed Drives of Agricultural Machinery

The operation of pumping units in drainage and water supply systems shows that there is overheating of electric motors. For the most part, this situation occurs with deep speed control of the electric machine. The acceptable range of rotor speed is important for variable-speed drives. For the most part, the upper limit of this speed is associated with the acceptable levels of stator winding temperature. The known formulas for calculating temperature exceedance mainly use named units, which limit their application. The paper derives the formula to calculate temperature exceedance in relative units to account for the load, insulation class, and ambient temperature. The bottom line is to reduce the relative rotor speed to 0.7 for most agricultural electric drives. The use of the proposed methodology for determining the allowable reduction in speed of electric motors of pumping units will allow increasing the service life of electric machines.