The calculation of starting resistances and configurations of the acceleration relay

Abstract

The initial data for calculating the starting resistances are the following quantities: 1.Power and type of the drive motor; for the latter, the following must be obtained from catalogues: a) the ratio of the breakdown (maximum) torque to the rated torque; b) the rated rotor voltage; c) the rated rotor current; d) the efficiency of the motor; e) the synchronous and rated rotational speeds of the motor; 2. Calculated values of the starting torque; 3. Values of the static resistance torques corresponding to the starting period; 4. Number of steps of the rotor rheostat; 5. The starting period t1 and the entire period of the working cycle T, including the pause θ, in accordance with the given speed diagram (Fig. 1). The basis for calculating the starting resistances should be the mechanical characteristics of the motors, which must be constructed in advance (Fig. 2). In this context, one very important condition must be noted: not every motor of a given power rating will be able to meet the required starting conditions with a predetermined number of steps in the starting rheostat circuit, because the necessary range of variation of the starting torque cannot be maintained for just any magnitude of the motor's breakdown torque. To finally determine the individual steps of the rheostat, it is necessary first to determine the required operating time for each step, i.e., the duration during which one step is energized, as well as the magnitude of this current.

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