A 400 V, 50 Hz, 4-pole, 3-phase, star-connected induction motor has the following data: stator impedance per phase is (0.7+ j 0.4), rotor impedance per phase referred to stator side is (0.3 + j 0.2) §, magnetizing reactance per phase is 30 N. The machine is operating at a slip of 4%. Draw the exact equivalent circuit and determine: stator current, motor power factor, input power, and rotor current?

A 3-0, 50-Hz induction motor with its rotor star-connected gives 500 V (r.m.s.) at standstill between slip-rings on open circuit. Calculate the current and power factor in each phase of the rotor windings at standstill when joined to a star-connected circuit, each limb of which has a resistance of 10 Q and an inductance of 0.03 H. The resistance per phase of the rotor windings is 0.2 Q and inductance 0.03 H. Calculate also the current and power factor in each rotor phase when the rings are short- circuited and the motor is running with a slip of 4 per cent. [13.6 A, 0.48; 27.0 A, 0.47] (London University) A 4-pole, 50-Hz, 3-phase induction motor has a slip-ring rotor with a resistance and standstill reactance of 0.04 2 and 0.2 2 per phase respectively. Find the amount of resistance to be inserted in each rotor phase to obtain full-load torque at starting. What will be the approximate power factor in the rotor at this instant ? The slip at full-load is 3 per cent. [0.084 2, 0.516 p.f.]…

T-a. The direction of rotation of a single-phase split-phase motor can be change by........ a) reversing the connection of the start winding b) reversing the connection of the run winding c) reversing the connection of the start and run winding at the same time d) "a" or "b", not "c" T-b. Single-phase split-phase motors using an electrolytic capacitor in the start winding circuit should not be cycled more than about__________ time per hour. a) 8 b) 12 c) 24 d) none of the above T-c. When replacing the capacitor in a capacitor-start induction-run motor, one must be sure to replace the bad capacitor with__________ . a) a smaller one b) one of the same size c) a larger one d) none of the above

A) Although the magnetic field for each phase of a 3-phase induction motor is merely switching back and forth between north and south poles, the resultant magnetic influence from all phases sets up a rotating magnetic field to cut the rotor conductors. a) true b) false B) In a two-pole stator winding of a 3-phase motor, how many revolutions does the rotating tr) magnetic field make in one cycle of the electrical current? a) one b) 60   c) 3600 d) none of the above

3.An induction motor has a rotor resistance and reactance at standstill of 0.1 ohm and 3.5 ohm respectively. At standstill the voltage induced to the rotor is 60volts per phase. If the slip is 5%, determine the rotor current

Q3 A 50 Hz split-phase induction motor has a resistance of 50 and an inductive reactance of 200 in the main winding as well as starting winding. Determine the value of resistance and capacitance to be added in series with the starting winding to send the same current in each winding with a phase difference of 90°. Ans[ 14.99 Ω, 127.5μF]

Armature reaction in an alternator primarily affects:   A: rotor speed  B: terminal voltage per phase  C: frequency of armature current  D: generated voltage per phase

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

Which of the following statements about three-phase induction motor is false  (A) The speed of rotation of the magnetic field is called the synchronous speed. (B) A three-phase supply connected to the rator produces a rotation magnetic field. (C)The rotating magnetic field has a constant speed and constant magnitude. (D) It is essentially a constant speed type machine.

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