RME Technical Subjects Test 11

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#1. The stray losses in the transformer will be reduces if _____ .

a. the liminations are thick

b. number of turns in the primary in winding is reduces

c. the number of turns in the secondary winding is reduces

d. the liminations are thin and the core is ferromagnetic

#2. The speed of DC series motor at no load is _____ .

a. zero

b. 1500 rpm

c. Very fast

d. 3000 rpm

#3. The function of commutator in DC generator is _____ .

a. to change alternating current to direct current

b. to improve commutation

c. for easy control

d. to change alternating voltage to direct voltage

#4. In practice the rotation of electric motor referred to its back is ______ .

a. clockwise

b. counterclockwise

c. forward

d. reverse

#5. How many contactor is needed to reverse the rotation of a three phase motor _____ .

a. three

b. four

c. six

d. one

#6. For the equal output the total current is more in ______ .

a. wave winding

b. lap winding

c. simplex lap winding

d. none of the above

#7. What is standard instrument to measure the speed of a motor?

a. pyrometer

b. gyrometer

c. tachometer

d. synchroscope

#8. If the field of a synchronous motor is under excited the Power factor will be _____ .

a. lagging

b. leading

c. unity

d. more than unity

#9. In a small dc machine, armature slots are sometimes not made axial but skewed. Though skewing makes winding a little more difficult, yet it result in_______________________.

a. Quiter operation

b. slight decrease in loss

c. Saving of copper

d. decrease power loss

#10. In a given machine. How may the no? Of parallel paths be increased in the armature of lop connected.

a. Increasing the number of magnetic pole

b. Increasing the excitation

c. Decreasing the speed

d. Parallel path is constant, it cannot be altered

#11. In the design of Power Supply, transformer should not be place near the component because of vibration/humming due to _______.

a. magnetostification

b. magnetostriction

c. ferroresonance

d. harmonics

#12. Which of the following motor is used in the Electric train?

a. AC series motor

b. Induction motor

c. DC series motor

d. Synchronous motor

#13. Which of the following motors has high starting torque?

a. DC shunt motor

b. Squirrel cage induction motor

c. DC series motor

d. AC series motor

#14. Which transformer has only one winding?

a. distribution

b. power

c. autotransformer

d. isolated winding transformer

#15. What is the equation for the DC generator?

a. E= VT+IaRa

b. E= VT-IaRa

c. E=-VT+IaRa

d. E=-VT-IaRa

#16. The dummy coil in the DC machines is used to ___________.

a. climate armature reaction

b. bring out mechanical balance of armature

c. eliminate reactance voltage

d. none of the above

#17. A generator has a commercial efficiency of 95% and a mechanical efficiency of 97%. Find the electrical efficiency.

a. 97.94%

b. 92.12%

c. 96%

d. 91.25%

#18. A part of a generator that links the generator to the prime mover __________.

a. yoke

b. brush

c. shaft

d. stator

#19. A magnet is being heated to a temperature of 460°. What do you think will happen?

a. it will become a loadstone

b. Magnetic field will increase

c. It will produce demagnetization

d. Magnetism will disappear

#20. What should be the possible no. of poles to obtain the highest operating speed?

a. 1

b. 2

c. 3

d. 4

#21. _______________ the slot teeth will make the DC generator quieter in operation.

a. Chamfering

b. Slotting

c. Pulsating

d. Commutating

#22. Transformer core uses small frequency because is laminated _________.

a. because it is difficult to fabricate solid core of high frequency

b. because laminated core operating at low frequency provides high flux density

c. to minimized eddy current and hystressis losses

d. to increase the main flux

#23. The mechanical power developed by the DC motor is maximum when ________.

a. back e.m.f is equal to applied voltage

b. back e.m.f. is equal to zero

c. back e.m.f. is equal to half the applied voltage

d. no load

#24. A generator may lost residual magnetism because of excessive ______.

a. vibrator

b. heating

c. over-excitation

d. varying loads

#25. Which among the following types of motor with same power rating having the same voltage level is the heaviest?

a. single phase Motor

b. DC shunt Motor

c. Induction Motor

d. DC compound Motor

#26. Electric power is transformed from one coil to the other coil in a transformer ______.

a. Physically

b. magnetically

c. Electrically

d. electromagnetically

#27. Electric motors are rated in ________.

a. kW

b. HP

c. kWH

d. kVA

#28. A hot smoky motor is a good indication of:

a. A ground

b. An open

c. A and B

d. A short

#29. A transformer is more efficiently utilized when the load has a ______ power factor.

a. low

b. medium

c. average

d. high

#30. What is the turns ratio on a three-phase, four wire 480/240/120 volt transformer?

a. 3/1

b. 2/1

c. 4/1

d. 1⁄2

#31. With a 3Ø delta-wye connected transformer 480 V primary, 208/120 V secondary, the secondary line current is ________.

a. equal to the secondary phase current

b. greater then the secondary phase current

c. less than the secondary phase current

d. 1.732 times the secondary phase current

#32. On a delta three-phase four-wire secondary, how many hot wires may use the common neutral?

a. 1

b. 2

c. 3

d. 4

#33. A 25 kVA, 2400/240 volt transformer has a primary current of 10 A. What is the secondary current?

a. 0.10 A

b. 100 A

c. 20 A

d. 50 A

#34. The standard method of controlling the output voltage of a 440 V, 60 Hz AC generator is accomplished by adjusting the ____________.

a. number of poles

b. prime mover speed

c. alternator’s field excitation

d. load on the alternator

#35. The transformer oil used in a transformer provides ____________.

a. insulation and cooling

b. insulation, cooling and lubrication

c. insulation and lubrication

d. cooling and lubrication

#36. What is the common method of cooling transformer?

a. natural cooling

b. air cooling

c. air blast cooling

d. oil cooling

#37. In a squirrel cage induction motor, which component is NOT a part of the motor?

a. stator

b. slip rings

c. fan blades

d. rotor

#38. A 25-hp engine drives a DC generator, if the generator has an efficiency of 84%, how much does it deliver?

a. 20 hp

b. 24 hp

c. 21 hp

d. 25 hp

#39. In a DC circuit, the ratio of watts to voltamperes is always _________.

a. unity

b. greater than

c. less than one

d. cannot tell what it might be

#40. What is common in the two windings of a transformer?

a. electric circuit

b. magnetic circuit

c. winding wire gauge

d. none of these

#41. Preferably, the resistance between the primary and the secondary of a transformer should be ___________.

a. as low as possible

b. as high as possible

c. low or high depending upon whether it is step up or step down respectively

d. high or low depending upon whether it is step up or step down respectively

#42. The resistance of low voltage side of a transformer __________.

a. is equal to resistance of its high voltage side

b. is more than resistance of its high voltage side

c. is less than the resistance of its high voltage side

d. (b) or (c)

#43. The basic property of the transformer is that it changes the voltage level of an a.c. signal _______.

a. without changing the power

b. without changing its shape

c. without changing its frequency

d. without changing power, frequency or shape

#44. Transformers are rated in ___________.

a. KW

b. KV

c. KWH

d. KVA

#45. What type of core is used for a high frequency transformer?

a. Air core

b. Closed iron core

c. Aluminum core

d. Open iron core

#46. Which of the following is a correct statement about eddy currents?

a. Eddy currents improve the efficiency of a motor

b. Eddy currents heat up the metal parts

c. Eddy current do not influence the movement

d. Eddy currents are used for arc welding

#47. Which of the statement given below is true about autotransformer?

a. It has two separate windings connected in series externally

b. It can only step down the voltage

c. It has only one winding

d. It is most suitable for power transformer

#48. Power transformers are designed to have maximum efficiency at __________.

a. no load

b. half load

c. near full load

d. little more than full load

#49. The size of a transformer core will depend on _____________.

a. frequency

b. flux density of the core material

c. area of the core

d. (a) and (b) both

#50. In any transformer the voltage per turn in primary and secondary remains ___________.

a. always different

b. always same

c. always in ratio of 1

d. sometimes same

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