01․ The torque developed in IM is nearly proportional to
02․ In case of 3 - ÃŽÂ¦ IM, plugging means
An IM can be quickly stopped by simply inter changing any of its two stator leads. It reverses the direction of the rotating flux which produces a torque in the reverse direction, thus applying brake on the motor, this is called plugging.
03․ When R2 is rotor resistance, X2 the rotor reactance at supply frequency and s the slip, then the condition for maximum torque under running condition will be
04․ The rotor electromotive force of the IM is observed to make 100 complete alterations per minute, calculated slip
100 alterations per minute = 100 / 60 cycles/sec. sf = 1.6667 Hz. ∴ s = 1.6667 / 50 = 3.33 %.
05․ Which of following methods are suitable for the speed control of squirrel cage induction motor? 1. Voltage control. 2. Frequency control. 3. Pole changing method. 4. Rotor resistance control select the correct answer using the codes given below:-
Since rotor resistance control is suitable only for woumd rotor induction motors.
06․ In a star - delta starting of an IM
When the motor is star connected star, the applied voltage over each phase is reduced to ( 1 / √3 ) times of the supply voltage. ∴ Line phase voltage is 57.7 % of line voltage.
07․ A 3 - φ induction motor can also be referred to as a
The rotor of a 3 - φ IM can never run at synchronous speed. Because at synchronous speed the flux cutting between the stator and rotor is zero leading to no torque production, thus bring the rotor speed immediately below synchronism.
08․ Which of the following methods of speed control is not affected through stator side?
The rotor resistance can only be added onto the rotor side and the other three modifications can be done from the stator side.
09․ The wound rotor type IM is used for____________ speed operation.
In this type of IM, the rotor has the same number of poles as the stator and the windings are made of wire, connected to slip rings on the shaft. Carbon brushes connect the slip rings to an external controller such as a variable resistor that allows changing the motors slip rate, by this motor can obtain variable speed.
10․ The rotor speed of an induction motor is given by
The rotor speed of an IM is given by Nr = ( 1 - s)Ns. It is seen that the motor speed can be changed by change in frequency f, number of poles P, or slip s.