Contents
What is the role of AC input frequency in an induction motor?
The dc current in the stator generates a stationary magnetic flux in the motor air gap. Rotation of the rotor in this field induces ac currents in its windings. The frequency of these currents decreases with rotor speed so as to set up a magnetic field that is stationary with respect to the stator.
What is the effect of variation of supply frequency in an induction motor?
A frequency higher than the rated frequency usually improves the power factor but decreases locked-rotor torque and increases the speed and friction and windage loss. At a frequency lower than the rated frequency, the speed is decreased, locked-rotor torque is increased, and power factor is decreased.
Why is the efficiency of an induction motor so poor at high slips?
So (1—s)P2 is converted to mechanical power, to which you can subtract mechanical losses to get shaft output. From this it is clear that for a given input the shaft output decreases as slip increases and hence the efficiency decreases at higher slip in the stable operating region.
What is relation between speed and frequency?
The relationship of the speed of sound, its frequency, and wavelength is the same as for all waves: vw = fλ, where vw is the speed of sound, f is its frequency, and λ is its wavelength.
How does voltage and frequency affect induction motors?
Effect of Variation of Voltage and Frequency Upon the Performance of Induction Motors (NEMA 14030) “Induction motors are at times operated on circuits ofvoltage or frequency other than those for which the motors are rated. Under such conditions, the performance ofthe motor will vary from the rating.
How does an induction motor work in a transformer?
When the induction motor starts the rotor winding is stationary and maximum voltage is induced in the rotor which will produce maximum rotor current. At starting the rotor is stationary and acts in a similar to a transformer with its secondary winding short circuited except that there is an air gap in the motor.
What are the voltage and frequency requirements for universal motors?
In accordance with NEMA MG 1, 12.44, motors shall operate successfully under running conditions at rated load with variation in the voltage up to the following percentages of rated voltage: Universal motors except fan motors – plus or minus 6 percent (with rated frequency).
How much variation does an alternating current motor need to have?
Alternating – current motors shall operate successfully under running conditions at rated load with a combined variation in the voltage and frequency up to 10 percent above or below the rated voltage and the rated frequency, provided that the frequency variation does not exceed 5 percent.