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The concept of Minimum - Base - Maximum speed of a motor in VFD operation

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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. 
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Types of Duty of Induction Motor

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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 ...
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Effect of change in Frequency in Induction Motor

The frequency of the supply voltage applied to an induction motor has a direct effect on the motor’s speed and torque. The speed of an induction motor is given by the equation: Speed = (120 x Frequency) / Number of Poles This equation shows that the speed of an induction motor is directly proportional to the frequency of the supply voltage. Therefore, if the frequency of the supply voltage is increased, the speed of the motor will increase. Conversely, if the frequency of the supply voltage is decreased, the speed of the motor will decrease. The torque produced by an induction motor is also affected by the frequency of the supply voltage. The torque produced by an induction motor is proportional to the square of the supply voltage and inversely proportional to the frequency of the supply voltage. Therefore, if the frequency of the supply voltage is increased, the torque produced by the motor will decrease. Conversely, if the frequency of the supply voltage is decreased, the torque pro...
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