Friday, 20 January 2017

THREE PHASE AND SINGLE PHASE INDUCTION MOTOR QUESTIONS FOR PRACTICE

motor



1.                  Explain construction and working principle of a 3-phase indcuiton motor.

2.                  Explain the terms slip, slip frequency, wound rotor and cage rotor.

3.                  Draw and explain the torque-slip & torque-speed charactoristics of a typical 3-phase induction motor. Mark the starting torque and maximum troque on the daigram so drawn.

4.                  Explain  the terms air-fap power Pg, inernal mechanical power developed and shaft power Psh. How  are these terms related with each others. Hence show that :
Pg :Rotor ohmic loss : Pm =1 :s (1-s)


5.                  A 3-phase induction motor runs at 1140 rpm at full load when supplied with power from a 60 Hz, 3-phase line calculate                                       
                        (i)         No of poles.
                        (ii)        Slip at full load.
(iii)             Frequency of rotor voltage.
(iv)             Speed of rotor field with respect to rotor.
(v)               Speed of rotor field with respect to stator and stator field.
(vi)             Speed of rotor at a slip of 10% and rotor frequency at this speed.
(vii)           If the applied voltage per phase is 230 V, find th0 rotor induced emf at stand still and at 10% slip, with stator to rotor turn ration of 1: 0.5
(Ans: - (i) 1200 rpm, (ii) 5% (iii) 3 Hz (iv) 60 rpm (v) 0 rpm (vi) 1080 rpm, (vii) 11.5 V)

6.                  A 6-pole, 3-phase indcution motor develops 30 hp including 2 hp mechanical losses at a speed of 950 rpm on 550 V, 50 Hz mains. The power factor is 0.88 lagging. Calculate (i) slip (ii) torot copper loss (iii) total input if stator losses are 2 kW (iv) efficiecny (v) line current. (Ans : - (i) 0.05, (ii) 1161 Watts, (iii) 20594 Watts, (iv) 81.64% (v) 30 A)
7.                  Explain construction and principle of operation of 1-phase induction motor.
8.                  Why single phase induciton moto is not self starting ?
      9.          What are the different methods of statring a single phase induction motors and what are                        the different types of 1-phase induction motors ?

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