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CBSE Class-12 Question Papers for IOP/Comptt Examination 2017 : All India Scheme, Electrical Machines

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Class 12 papers

CBSE Class-12 Question Papers for IOP/Comptt Examination 2017 :

All India Scheme, Electrical Machines

ELECTRICAL MACHINES
(Theory) Paper II

 

Time allowed : 2 hours

Maximum Marks : 40

Instruction : Attempt all questions.

SECTION – A

1. Attempt any seven questions :
(A) Which winding in a transformer has more number of turns ?
(i) Primary winding (ii) Secondary winding
(iii) High voltage winding (iv) Low voltage winding

(B) In an 8 pole wave connected d.c. motor armature, the number of parallel paths are
(i) 8 (ii) 4
(iii) 2 (iv) 16

(C) Most suitable d.c. motor for electric traction is
(i) d.c. shunt motor (ii) d.c. series motor
(iii) d.c. compound motor (iv) None of the above

(D) Iron loss in a d.c. motor take place in
(i) Yoke only (ii) Armature core only
(iii) Yoke and Armature (iv) None of the above

(E) A universal motor is
(i) A.C. series motor (ii) D.C. series motor
(iii) Both A.C. and D.C. motor (iv) A 3-phase A.C. motor

(F) In a split phase motor main winding is of
(i) thick wire placed at the top of slot.
(ii) thick wire placed at the bottom of slot.
(iii) thin wire placed at the top of slot.
(iv) thin wire placed at the bottom of slot.

(G) Shaded pole motor has
(i) low starting torque (ii) poor efficiency
(iii) poor p.f. (iv) All of the above

(H) Three point starter can be used for
(i) shunt motor only (ii) compound motor only
(iii) series motor only (iv) Both shunt and compound motor

(I) Bit of soldering Iron is made of
(i) Aluminium (ii) Magnenin
(iii) Copper (iv) None of the above

(J) An alloy of 60% lead and 40% tin is called as
(i) Hard solder (ii) Soft solder
(iii) Bronze (iv) None of the above

SECTION – B

2. (A) Describe the construction of 1-phase transformer.
(B) Name the various types of single phase transformers on the basis of their
construction.
(C) What is the function of poles in d.c. motors ?
OR
What is the function of commutator in d.c. motors ?
(D) Name the various starters used to start 3-phase induction motors.
OR
Describe the construction of starter used to start 3-phase slip ring induction
motor.
(E) What is the principle of working of 3-phase induction motor.
(F) Name various methods of producing starting torque in 1-phase induction motors.
OR
What are various applications of single phase series motors ?
(G) What are various techniques used for soldering ?

SECTION – C

3. (A) What are various methods of cooling of transformers ? Explain them in brief.
OR
With the help of neat sketch explain the construction of shell type transformer.

(B) Why should d.c. motor not be started without starter ?
OR
Draw the circuit diagram of any one starter used for d.c. motors.

(C) How starting torque is produced in a shaded pole motor ?

4. (A) How a d.c. motor is installed ? Explain with the help of neat sketches.
OR
What are various methods of speed control of d.c. shunt motor ? Explain any one method.
OR
With the help of neat sketch explain the working of 4-point starter used in d.c. motor.

(B) What is universal motor ? Describe its various applications.
OR
Explain any one type of starter used to start 1-phase induction motor.

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