II Year PEE Unit-8 :Single phase induction motor bits

                               UNIT-VIII: Single phase induction motors

1. At starting, the line current of a capacitor start induction motor is ______ the normal full load current[ b ]

(a)8 to 10 times (b)4 to 5 times (c) equal to (d)7 to 8 times

2.  The main winding and starting winding of a single phase induction motor are connected in__________ across the supply. [b ]

(a)series (b) parallel (c)series parallel (d)none

3. In capacitor start induction motor the angle between Im and Is is about  75˚

4. The purpose of starting winding in a single phase induction motor is to produce rotating flux

5. A single phase induction motor employs squirrel cage rotor

6.  The main winding and starting winding of a single-phase induction motor are connected in ________ across the supply [b ]

(a) series (b) parallel (c) series-parallel (d) none of the above

7.  A two-phase a.c. servometer has [b ]

(a) wound rotor (b) cage rotor (c) wound or cage rotor (d) a rotor similar to that in d.c motors

8. A 50 Hz, 4-pole, single-phase induction motor will have a synchronous speed of 1500 RPM

9. The full-load efficiency of a shaded-pole motor is about 30 to 35 %.

10. The amount of torque required to move a stepper motor one full step is called  holding torque

II Year PEE Unit-7 Transformers bits

                        UNIT-7: TRANSFORMERS and Their Performance

1.     1. If rated Dc voltage is applied instead of AC to the primary of a transformer then primary winding of the transformer will burn.

      2. If Pi be the iron losses and Pc be the copper losses on full load, then the condition for obtaining the maximum efficiency at 3/4th full load is  

Pc= (16/9) Pi

  3. A transformer can have Zero regulation at leading power factor.

  4. the chemical used in breather is silica gel

   5. The no load current in a transformer lags the applied voltage by  75˚

6. Condition for maximum efficiency of Transformer is Constant losses =variable losses

7. In a Transformer Core is laminated to reduce    Eddy current loss

8.  A transformer has an efficiency of 80% and works at 100V, 4KW. If the secondary voltage is 240V, find primary current [a ]

(a)40A (b)30A (c)20A (d)10A

9.  The no load current of a transformer is generally of the order of _______the full load current [a ]

(a)less than 5% (b)more than 5% (c)equal to that (d)zero

10. The core losses in a transformer consists of Hysteresis and Eddy current losses

11. The voltage regulation of a transformer can be determined by conducting OC and SC tests.

12.  A transformer transfers electrical energy from primary to secondary usually with a change in [ a]

(a) frequency (b) power (c) voltage (d) time period

13.  The open-circuit test on a transformer is always made on [ a]

(a) low-voltage winding (b) high-voltage winding

(c) either low or high voltage winding (d) none of the above

14. The open-circuit test on a transformer gives Iron losses

15. A transformer has full-load copper loss of 400 W. The copper loss at half-full load will be 100W

16. Transformer operates on AC only.

17. A transformer steps up the voltage by a factor 100. The ratio of current in the primary to that in secondary is 100

18. If P_i be the iron losses and P_c be the full load losses, the load current at which maximum efficiency occurs is ____________ times of full load current

19. Efficiency of a transformer is maximum if  Iron losses=cu losses

20. The Iron core in a transformer provides a Low reluctance path to the main flux.

21.  The Principle of operation of a Transformer is  [  B]

(A) Electromagnetic Induction (B)Mutual Induction

(C) Varying a conductor in a magnetic field (D) Electrostatic induction

22.  The flux involved in the emf equation of a transformer has [   D]

(A) RMS value (B) Average value (C) Total value (D) Max. value

23.  In a single phase transformer, with subscripts 1 and 2 for primary and secondary windings[a ]

(A) E₁N₂= E₂N₁ and I₁N₁= I₂N₂ (B) E₁N₁= E₂N₂ and I₁N₁= I₂N₂

(C) E₁N₂= E₂N₁ and I₁N₂= I₂N₁ (D) E₁N₁= E₂N₂ and I₁N₂= I₂N_1s

24. The Regulation of a Transformer is zero, when the Power factor is leading

25.  Eddy current losses in a transformer core can be reduced by _____ [ a ]

(a) Reducing the thickness (b) decreasing air gap in the magnetic circuit

(c) Increasing air gap in the magnetic circuit. (d) Increasing the thickness

II Year PEE D.C.Motors bits

                                                 UNIT-6: D.C.MOTORS

1.  In a DC machine, the number of commutator segments is equal to [c ]

(a)number of conductors (b)number of poles (c)number of coils (d)both a and b

2.  Main advantage of differentially compound motor is that    [c  ]

(a)stable under heavy loads (b)speed increases to very high values on no load

(c)speed remains constant if load is not excessive (d)start under heavy load

3.  Which of the following motor should never be started on no load     [  d ]

(a)shunt (b)compound cumulative (c)compound differentially (d) series

4.  The yoke of a dc machine is made up of [  d ]

(a)silicon steel (b)soft iron (c)aluminium (d)cast steel

5.  The value of back emf in a dc motor is maximum at _______ [ a  ]

(a)no load (b)full load (c)half full load (d)one fourth full load

6. The brushes that carry the current to the load are made up of Carbon

7. Power lost as heat in the armature and field windings of a dc machine is called  copper loss

8. Series dc motor should never be started on no load.

9. The relation between speed, flux and backemf in a dc motor is   NαEb/Ф

10.  The field winding of a d.c shunt machine usually carries ______ of the rated current of the machine [  a]

(a) 2% to 5% (b) 15% to 20% (c) more than 20% (d) less than 0.5%

11.  The speed of a d.c. motor can be controlled by changing [ d   ]

(a) its flux (b) armature circuit resistance

(c) applied voltage (d) all of the above

12. By putting controller resistance in series with the armature of a d.c motor, we can obtain speeds

 [ b]

(a) above the normal speed only (b) below the normal speed only

(c) above as well as below the normal speed (d) none of the above

13.  The only disadvantage of field control method for controlling the speed of a d.c shunt motor is that it [  c]

(a) give speeds lower than the normal speed (b) is wasteful

(c) needs a large rheostat (d) adversely affects commutation

14. The motor terminal voltage equation is given by  V = E_b+ I_aR_a

15. The most economical method of finding no-load losses of a large d.c. machine is swinburne’s test.

16.  The Commutator in a dc machine can be convert [ c]

(a) ac to dc (b) dc to ac (c) both a and b (d) None of the above

17.  Fleming's left hand rule is applicable for: [b ]

(a) dc generator (b) dc motor (c) alternator (d) Transformer

19.. The armature torque of the dc shunt motor is proportional to [a ]

(a) armature current only (b) field flux only (c) armature current and flux both (d) None

20..  Motor which should not run at no-load is [a ]

(a) Series motor (b) shunt motor (c) compound motor (d) induction motor

21. Yoke is made of which material Cast iron or Cast steel

22 Losses in DC machine are Iron losses,Cu losses, Mechanical losses

23. Types of     DC motors , D.C series motor, d.c shunt motor

24. In DC shunt motor the Torque is directly proportional to Ia

25.  High permeability magnetic materials helps [a ]

A) To confine the flux within the magnetic circuit. B) To allow the flux to leak

C) In producing more current. D) None of the

26.  A Commutator in a DC machine can convert ____ to ______ [ c]

(a) AC, DC (b) DC, AC (c) either ‘A’ or ‘B’ (d) None

27.  The current flowing through armature conductors of a dc motor is _____________ [c ]

a) Pulsating b) Dc c) Ac d) none of these

28..  In Swinburne’s test of a Dc machine [ b]

a) No load losses are calculated and copper losses are measured

b) No load losses are measured and copper losses are calculated

c) Both the losses are measured

    d) Both the losses are calculated

29.  The supply terminals for a dc shunt motor are reversed. What will be effect on the motor [b ]

a) It will run as Dc generator b) runs in reverse direction c)it stops d)its burns

30. The starting resistance for a dc shunt motor  Low

31. A 3 point starter is considered suitable for dc Shunt motor

32.  The magnitude of force acting on a current carrying conductor placed in a magnetic field is

independent of [ c ]

A) Flux density B) length of conductor

C) cross-sectional area of conductor D) current flowing Through the conductor

35.  When a dc machine is connected in the dc supply main it will produce [ d]

A) Emf in opposition to applied voltage. B) Unidirectional torque

C) Copper losses in the windings D) all of the above

36.  Emf induced in each conductor of a DC Machine is [a ]

A) An alternating emf B) A direct emf

C) A pulsating emf D) Emf of random waveshape

37.  The starting torque of a dc shunt motor is [b ]

A) Zero B) low C) high D) very high.

38. The armature of a dc machine is a laminated to reduce  Eddy current losses

39. If the flux of a dc motor approaches zero its speed will Infinite

40. The direction of mechanical force experienced on a current carrying conductor placed in a magnetic Field is determined by Fleming’s left hand rule

41. The function of interpoles in a dc machine is to improve commutation

42 The speed of a DC motor is directly proportional to its Back emf and inversely proportional

To Flux

43. The current drawn by a dc motor at the starting instant will be High

44.  The eddy current losses is directly proportional to [ b ]

a) f b)f^2 c)f^1.6 d)f^3

45.  The iron losses [ d]

a) core losses b) eddycurrent losses c) hystersis losses d) all the above

46..  The speed of a d.c motor can be controlled by varying [d ]

a)its flux per pole b)resistance of armature circuit c)applied voltage d)all the above

47.. The collection of current from armature conductors to the external load is the function of Commutator and brushes

48. The iron or core losses are also known as Constant losses

49. In d.c motor unidirectional torque is produced with the help of-Brushes-and commutator.

50 Under constant load conditions, the speed of a d.c motor is affected by V, Ra, Ø

51. The Eb/V ratio of a d.c motor known as Efficiency

52. An invertor is employed to convert DC voltage to AC voltage

D.Generators bits with answers

                                       JNTUH PEE SECOND MID BITS                                   

                                               UNIT-5:   D.C. Generators

 1.The type of compound generator commonly used for obtaining an almost constant terminal voltage is[ ] (a) over compound (b)flat compound (c)cumulative compound (d)under compound  [   b]

2.  In a DC machine, the number of commutator segments is equal to [ c ]

(a)number of conductors (b)number of poles (c)number of coils (d)both a and b

3.  The yoke of a dc machine is made up of    [  d  ]

(a)silicon steel (b)soft iron (c)aluminium (d)cast steel

4. The brushes that carry the current to the load are made up of   Carbon

5. Power lost as heat in the armature and field windings of a dc machine is called COPPER loss.

6. A shunt generator delivers 195A at a terminal p.d of 250V. The Ra and Rf are 0.02Ω and 50Ω respectively. The generated emf is 254V

7.  The field winding of a d.c shunt machine usually carries ______ of the rated current of the machine [ a  ]

(a) 2% to 5% (b) 15% to 20% (c) more than 20% (d) less than 0.5%

8.  A shunt generator delivers 195 A at a terminal p.d of 250 V. The armature resistance and shunt field resistance are 0.02Ω and 50Ω respectively. What is the value of generated e.m.f? [  c ]

(a) 246 V (b) 270 V (c) 254 V (d) 282 V

9.  In a long-shunt compound-wound generator, the shunt field is connected parallel with [ d  ]

(a) armature (b) parallel combination of armature and series field

(c) series field (d) series combination of armature and series field

10. In a cumulatively compounded generator, the shunt and series fields  aid  each other

11. The e.m.f equation of a d.c generator in terms of flux, poles etc is given by Eg = (ΦZNP) / (60 * A)

12. The most economical method of finding no-load losses of a large d.c. machine is  Swinburne’s test.

13.  The Commutator in a dc machine can be convert [  c]

(a) ac to dc (b) dc to ac (c) both a and b (d) None of the above

14.  The emf produced in the dc generator is ____ induced emf [ b ]

(a) Statically (b) Dynamically (c) magnetically (d) Electrostatically

15..  DC generator operates on the principle of [  a]

(a) Electromagnetic induction (b) Lenz's law (c) Biov Savart's law (d) none of these

16. Emf equation of generator is  Eg = (ΦZNP) / (60 * A)

17. Yoke is made of which material   Cast iron or Cast steel

18. Types of windings in dc generator   Lap winding ,wave winding

19. The Mechanical energy source used to drive a dc generator is called a [ b  ]

(A) Rotor (B) Prime Mover (C) Alternator (D) Motor drive

20.  The nature of current having in the armature of a dc machine is _____ [ a ]

a) AC b) DC c) pulsating d) None

21.  The induced voltage in a single loop reverses_____ [  a ]

a) Once each revolution b) once each half revolution

c) one each quarter revolution d) 8 times each revolution

22.  The field of self excited generator is excited by [   c]

a) Dc b) Ac c) By its own current d) Either ac or Dc

23. The magnetic field which initially induces emf in the armature in a self excited dc generator is Because of Residual magnetism(residual flux)

24.  Emf induced in each conductor of a DC Machine is [ a ]

A) An alternating emf B) A direct emf

C) A pulsating emf D) Emf of random waveshape

25.  The residual magnetism of a DC shunt generator can be regained by [a ]

A) Connecting the shunt field to a battery B) Running the generator on no load for sometime C) Grounding the shunt field D) Reversing the direction of rotation of the generator.

26. Faraday's second Law states that the magnitude of individual emf is equal to the rate of Change of flux linkages.

27. A four pole DC generator is running at 1500 rpm. The frequency of current in the armature is 50Hz

28. The armature of a dc machine is a laminated to reduce Eddy current losses

29. The function of interpoles in a dc machine is to   improve commutation

30. The EMF induced in a coil rotating in a uniform magnetic field is maximum when the flux linkage by the coil is  minimum

31. The O.C.C of a d.c. generator is also called its magnetic or no load saturation characteristic.