The stator resistance, stator-referred rotor resistance and equivalent inductive reactance of a 400 V, 4-pole, 50 Hz, Y-connected induction motor are 0.22 Q, 0.25 Q and 3.5 Q, respectively. The motor is driving a constant load torque of 45 Nm at 1410 RPM. Calculate the motor speed and starting current if the supply frequency is reduced to 42 Hz. Compare and comment on the starting currents before and after the frequency is reduced. Assume that the rotational losses are negligible.

B/ Fill in the blanks: TV ezur 1- In a three-phase induction motor iron losses in stator will be..... that in rotor. 2- In three-phase induction motors sometimes copper bars are placed deep in the rotor to........... 3- Blocked rotor test on induction motors is used to find out. R..., ke, X. 4- The maximum torque in an induction motor depends on .............and .....

6- Which of the following supply is given to the rotor winding of 3-Phase Induction Motor: a) DC Supply b) AC Supply c) No Supply d) Pulsating Supply 7- 3-Phase Induction Motor will have Starting Torque and Starting Current a) High, High b) Low, Low. c) High, Low d) Low, High 8- Which of the following method is used for controlling the speed of an induction motor: a) Changing number of stator poles b) Supply voltage control c) Frequency control d) All the options are correct 9- Which of the following method cannot be used for starting of 3-Phase Squirrel Induction Motor: a) Star-Delta Starting b) Line resistor startling c) transformer Starter d) Rotor Resistance Starting 10- The rotor of a stepper motor has no: a) windings b) commutator c) brushes d) all of the above

An 8 pole, 50 Hz slip ring induction motor runs at a slip of 2.67% on full load. The rotor resistance per phase of the winding is 0.2 ohm. What external resistance per phase must be added in the rotor circuit so that the motor now runs ate a slip of 17.33% such that the torque remains same in both the cases. (Ans: 1.1 ohm)

A three –phase, 440V, 50 Hz, 6 – pole induction motor running at 950 rpm takes 50 kW at certain load. The friction and windage loss is 1.5 kW and the stator losses = 1.2 kW. Determine the output from the rotor. (a). 42.68 kW                 (b). 46.48 kW (c). 48.80 kW                 (d). 44. 86 kW

A 3-phase, 50-Hz induction motor with its rotor star-connected gives 500-V(r.m.s.) at standstill between the slip-rings on open-circuit. Calculate the current and power factor at standstill when the rotor winding is joined to a star-connected external circuit, each phase of which has a resistance of 10 Q and an inductance of 0.04 H. The resistance per phase of the winding is 0.2 Q and its inductance is 0.04 H. Also, calculate the current and power factor when the slip-rings are short-circuited and the motor is running with a slip of 5 per cent. Assume flux remain constant.

What is the relationship between slip s) and load (Pa) in an induction motor? Please explain.

Draw the typical speed-torque characteristic of the induction motor and expain it.

A value of magnetizing current in a 3-phase induction motor * gives power factor smaller .. larger smaller. .poor large . better O large...poor O

A 3-phase, 50-Hz induction motor with its rotor star-connected gives 500 V (r.m.s.) at standstill between the slip-rings on open-circuit. Calculate the current and power factor at standstill when the rotor winding is joined to a star-connected external circuit, each phase of which has a resistance of 10 Q and an inductance of 0.04 H. The resistance per phase of the rotor winding is 0.2 N and its inductance is 0.04 H. 4. Also, calculate the current and power factor when the slip-rings are short-circuited and the motor is running with a slip of 5 per cent. Assume the flux to remain constant. Identify it`s given and solve it