Low Voltage Motor - AC Induction Motor

In general, in an enquiry sheet for motors which will be running with VVVFD, the speed range may read as below 0-500-1200 0-1000-1500 100-750-1000 The meaning of this speed range is that the within the first two speed the motor should provide constant torque, and at the last or the highest speed the motor is expected to provide constant power. For a 50Hz motor, Constant Torque Zone will be limited up to 50Hz. For a self cooled motor it may be from 30Hz to 50Hz and for a forced cooled motor it may be from 10Hz to 50Hz.  Constant power zone is that zone which is beyond motor rated frequency. in this zone Voltage becomes constant and the frequency is increasing. hence V/f ratio will not be maintained and thus the torque will fall. However, upto certain speed the power will be constant. In constant power zone the rated torque of the motor will be  Tnom ∝ 1/ Nop Tnom = nominal or rated torque Nop = operating speed. Hope this is okay to understand. 

  This overload cycle is common for mill duty motors. The motor manufactures usually get enquiry from the users with corresponding duty cycle. it is advisable to send such enquiries to the design team for proper selection not only in terms of frame size and KW, but also he temp rise of the motor. for such cases RMS overload needs to be calculate. I am providing example for better understanding of the calculation Condition 1: 160% overload for 60 sec in every 600 sec so in a 300 sec cycle , the motor will run with 100% load for (600-60) = 540 sec So the RMS overload is = √((160^2) x 60 + (100^2) x 540) / 600) ( √ for total calculation to be considered ) = 107.5% Condition 2: 150% overload for 60 sec 175% for 20 sec so 100% loading for a 600 sec cycle will be = (600-60-20)=520 sec So the RMS overload is = √((150^2) x 60 +(175^2) x 20 + (100^2) x 520) / 600) ( √ for total calculation to be considered ) = 109% For any clarification please ask question.

Type of Duty - Induction Motor   Cyclic Duty Factor ( CDF ): The cyclic duration factor is the time during which motor heating takes place. It is the ratio between the total time which contributes to electrical heating in one cycle and the complete cycle time. This is the most common and available in market and industry. Type of Duty - S1 Operation at constant load long enough for a thermal steady state condition to be reached. P = Load Pv = Electrical losses θ = Temperature θmax = Max. temp attained t = time Type of Duty - S2 Operation at a constant load for a given time which will not allow the motor to reach thermal equilibrium followed by rest and de energized.  You may find the usage in siren of any Industry . It will run for a while and then again after a specific period. P = Load Pv = Electrical losses θ = Temperature θmax = Max. temp attained t = time ∆tp = Operation time at constant load Type of Duty - S3 Combination of duty cycles which consist of Operation at ...