Determination of Power Rating of Three-Phase Induction Motors which Work Frequently, Intermittently, and Periodically Based upon Losses

This paper proposes a novel approach for determining the power rating of three-phase induction motors which work frequently, intermittently, and periodically based upon losses. The approach is also based on the following aspects: (1) there are several processes in a period; (2) the output power of a process varies with time; (3) the experienced time of a process, the switched-off time between two adjacent processes, and the cycle time are perhaps very short; (4) the rotational angle of the motor in a process is given; (5) the moment of inertia and the load torque of the motor drive system referred at the motor axis in a process are provided. The relationship between total losses and slip is formulated and the motor drive model differential equation presented. From the relationship and the differential equation, the heat due to losses of a process can be calculated, and then the total heat of a period can also be worked out. Accordingly, the average total losses of a period can be obtained by dividing the ...