DC Motors 7

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Objective Questions with Answers for Electrician and Wireman: DC Motors 7

Subject: DC Motors 7

Part 7: Objective questions and answers of DC Motors


Q1. The starting resistance of 3 point starter in D.C. motor is connected with:

a) Parallel across the armature

b) Series with the armature

c) Parallel across the field winding

d) Series with the field winding


Q2. In a four point starter the protective resistor is connected in series with:

a) Overload coil

b) No volt coil

c) Armature

d) Shunt field


Q3. The starting current of a 220V, 10HP shunt motor having an armature resistance of 0.2 ohms, without starter is:

a) 11 amps

b) 110 amps

c) 1100 amps

d) 11000 amps


Q4. A 220V DC machine has an armature resistance of 0.5 ohm. If the armature current is 20 amps, the induced emf when the machine works as (i) generator (ii) motor will be:

a) 230V, 210V

b) 210V, 230V

c) 200V, 230V

d) 190V, 240V


Q5. A DC shunt motor is running on no-load if the field winding gets opened, what will be the condition of the motor?

a) The motor will stop

b) The motor will burn out

c) The motor will run at high speed

d) The motor will make noise


Q6. In DC shunt motor, if the field is opened during running, what will happen to the motor?

a) The direction of rotation will be reversed

b) The speed will decrease

c) The motor runs in dangerous speed and may bum out

d) The motor will not stop


Q7. The D.C shunt motor speed is to be varied from zero to above normal with reversing facility having inherent stability of speed at all loads. What speed control method is to be used?

a) Supply voltage speed control method

b) Ward-Leonard system of speed control

c) Shunt field control method

d) Armature speed control method


Q8. What is the cause for the DC motor's brush makes chattering or hissing noise during operation?

a) Overloading

b) Insufficient brush tension

c) Short circuit in commutator segment

d) Incorrect brush spring pressure


Q9. The armature reaction effect in a synchronous machine depends on

a) Load current

b) Power factor of the load

c) Speed of the machine

d) Both 'A' and 'B'


Q10. The alternators are rated as:

a) Kw

b) Kvar

c) Kva

d) Kwh


Q11. A10 pole alternator rotates at a constant speed of 1200 rpm. The periodic time of voltage in seconds per Cycle will be

a) 0.01

b) 0.02

c) 0.04

d) 0.08


Q12. The D.C. and A.C. generators are similar in one important function. That is the…….

a) Generated emf is a direct current

b) Generated emf is an alternating current

c) Generated emf is a pulsating current

d) Generated emf is an oscillating current


Q13. Which one of the following is the reason for using dampers in large alternator work?

a) To increase stability

b) To increase output

c) To decrease output

d) To reduce voltage fluctuation


Q14. A large diameter of alternator is running at slow speed will be having…….

a) Rotating alternator

b) Rotating field with a smooth cylindrical rotor

c) Rotating field with a salient pole rotor

d) Rotating armature with field


Q15. A 3-phase, delta connected alternator having a rotating armature will have:

a) 2 slip rings

b) 3 slip rings

c) 4 slip rings

d) 6 slip rings


Q16. Which instrument is used to indicate the correct time for synchronization of two alternators?

a) Phase sequence meter

b) Synchroscope

c) Power factor meter

d) Tachometer


Q17. The reason for the stator core of an alternator is made up of laminated sheets is to…….

a) Increase the eddy current losses

b) Reduce the eddy current losses

c) Increase the magnetic flux

d) Decrease the speed of the rotor


Q18. The alternators are rated in…….

a) KVA

b) KW


d) Ampere hour


Q19. The frequency of 96 pole alternators, running at 1500 rpm is:

a) 75 Hz

b) 60 Hz

c) 50 Hz

d) 40 Hz


Q20. An alternator is running at a speed of 1500 rpm, at the frequency of 50 Hz, calculate the number of poles?

a) 8

b) 6

c) 4

d) 2


Part 7: Objective questions and answers of DC Motors


Q1. Answer b

Q2. Answer b

Q3. Answer c

Q4. Answer a

Q5. Answer c

Q6. Answer c

Q7. Answer b

Q8. Answer d

Q9. Answer d

Q10. Answer a

Q11. Answer a

Q12. Answer b

Q13. Answer a

Q14. Answer c

Q15. Answer b

Q16. Answer b

Q17. Answer b

Q18. Answer a

Q19. Answer a

Q20. Answer c

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