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Electrical Machines Evaluation Test: Multiple Choice Questions and Answers, Exams of Electrical Engineering

University of the Philippines Open UniversityElectrical Engineering

A comprehensive evaluation test in electrical machines, covering various aspects of the subject. It includes multiple-choice questions with answers, designed to assess understanding of key concepts and principles. The test covers topics such as shunt generators, transformers, dc motors, and ac generators, providing a valuable resource for students preparing for exams or seeking to reinforce their knowledge.

Typology: Exams

2024/2025

Available from 04/05/2025

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TECHNOLOGICAL INSTITUTE OF THE PHILIPPINES,QC
ELECTRICAL ENGINEERING DEPARTMENT
Evaluation Test in ELECTRICAL MACHINES
NAME_____________________________ SCORE______________
MULTIPLE CHOICE. Write the letter that correspond as best answer. Use the space provided
before the number. (Analyze the problem carefully). If your answer is not among the choices, write
N and justify your answer.
1. Shunt generator are used where the main requirement is a constant
A. current and voltage C. voltage over a wide load range
B. current D. voltage over a narrow load range
2. If a self-excited dc generator after being installed , fails to build up on its first trial run, the first
thing do is to…
A. increase the filed resistance
B. check armature insulation resistance mover
C. reverse field connections
D. increase the speed of prime
3. 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)
4. The primary and the secondary voltage of TRANSFORMER are
A. 180o out of phase
B. always in phase
C. 90o out of phase
D. 30o or 60o out of phase
5. The basic property of the transformer is that it changes the voltage level of an AC signal,
A. Without changing the power
B. Without changing the shape
C. Without changing its frequency
D. Without changing power frequency and shape
6. The induced emf in the transformer secondary will depend upon
A. maximum flux in the core and frequency only
B. frequency , flux and number of turns in the secondary
C. frequency and supply only
D. number of turns in the secondary only
7. The principle of working of a transformer
A. static induction C. mutual induction
B. dynamic induction D. self induction
8. For both lap and wave windings, there are as many commutator bars as the number of?
A. poles C. windings elements
B. slots D. armature conductor
9. Eddy current losses in transformer core are reduced by
A. increasing the thickness of laminations
B. decreasing the thickness of laminations
C. taking the wire of higher gauge for winding the transformer
D. decreasing the air gap in the magnetic circuit
10. The field poles are made of iron either solid or laminations and support coiuls of wires called
A. field windings C. the armature
B. interpoles D. the commutator
pf3
pf4
pf5

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Download Electrical Machines Evaluation Test: Multiple Choice Questions and Answers and more Exams Electrical Engineering in PDF only on Docsity!

TECHNOLOGICAL INSTITUTE OF THE PHILIPPINES,QC ELECTRICAL ENGINEERING DEPARTMENT Evaluation Test in ELECTRICAL MACHINES NAME_____________________________ SCORE______________ MULTIPLE CHOICE. Write the letter that correspond as best answer. Use the space provided before the number. (Analyze the problem carefully). If your answer is not among the choices, write N and justify your answer.

  1. Shunt generator are used where the main requirement is a constant A. current and voltage C. voltage over a wide load range B. current D. voltage over a narrow load range
  2. If a self-excited dc generator after being installed , fails to build up on its first trial run, the first thing do is to… A. increase the filed resistance B. check armature insulation resistance mover C. reverse field connections D. increase the speed of prime
  3. 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)
  4. The primary and the secondary voltage of TRANSFORMER are A. 180o^ out of phase B. always in phase C. 90o^ out of phase D. 30o^ or 60o^ out of phase
  5. The basic property of the transformer is that it changes the voltage level of an AC signal, A. Without changing the power B. Without changing the shape C. Without changing its frequency D. Without changing power frequency and shape
  6. The induced emf in the transformer secondary will depend upon A. maximum flux in the core and frequency only B. frequency , flux and number of turns in the secondary C. frequency and supply only D. number of turns in the secondary only
  7. The principle of working of a transformer A. static induction C. mutual induction B. dynamic induction D. self induction
  8. For both lap and wave windings, there are as many commutator bars as the number of? A. poles C. windings elements B. slots D. armature conductor
  9. Eddy current losses in transformer core are reduced by A. increasing the thickness of laminations B. decreasing the thickness of laminations C. taking the wire of higher gauge for winding the transformer D. decreasing the air gap in the magnetic circuit
  10. The field poles are made of iron either solid or laminations and support coiuls of wires called A. field windings C. the armature B. interpoles D. the commutator
  1. Pigtails are used on carbon brushes to_________ A. compensate for wear C. supply the proper pressure B. hold the brush in the holder D. make a good electrical connection
  2. Which of the following is not 180 degrees apart? A. XL and IC C. Ic and IL B. XC and IC D. XL and XC
  3. A transformer operates A. always at unity power factor B. has its own power factor C. at power factor below a particular value D. at power factor depending on the power factor of the load
  4. The laminations are made from A. low carbon steel C. nickel alloy steel stampings B. silicon sheet steel D. chrome steel sheets
  5. The steel for construction of transformer core is made so as to have A. low permeability and high hysteresis B. low permeability and low hysteresis C. high permeability and low hysteresis D. high permeability and high hysteresis
  6. The special silicon steel its used for laminations because A. hysteresis losses are reduced C. both the above losses are reduced B. eddy current losses are reduced D. none of these
  7. A VAR meter depends on the following values EXCEPT one. Which one of these? A. voltage C. sine of the phase angle B. current D. cosine of the phase angle
  8. The output voltage of a single loop generator is a A. steady d.c. C. pulsating a.c. B. steady a.c. D. pulsating d.c.
  9. A smooth output from a generator is obtained by a A. design of the armature winding B. changing the form of the commutator C. changing the field strength D. none of these
  10. An electric current is actually a…. A. beta emission C. flow protons B. Flow of electrons D. collision of molecules
  11. Determine the number of electrical degrees made per revolution for a 36 pole alternator A. 12,960 C. 4, B. 6,480 D. 3,
  12. A dc generator has a no-load output voltage rating of 120 Volts. Its armature circuit resistance is 0.95 ohm and its field coils are separately energized. If a load rated at 2 kW at 115 Volts is connected across the terminals , What power would be absorbed by the load? A. 1,670 watts C. 2,180 watts B. 2,000 watts D. 1,518 watts
  13. A supply delivers 45 Amp, 480 V, 0.8 power factor which of the following is the active power? A. 12960 C. 17280 B. 8640 D. 21600
  14. An a.c. generator driven at 375 r/min generates an e.m.f having a frequency of 50Hz. Calculate the number of poles? A.15 poles C. 17 poles B. 16poles D. 18 poles
  1. A coil is wound with 300 turns on a square former having sides 50 mm in length. Calculate the maximum value of the e.m.f. generated in the coil when it is rotated at 2000r/min in a uniform magnetic field of density 0.8T. What is the frequency of tis e.m.f? A. 126.5 V, 33.3Hz C. 162.5V, 33.3Hz B. 125.6 V, 33.3Hz D. 162.6V, 33.3Hz
  2. The power input to a 100 hp, 480 Volt , 85% efficiency and 75% power factor 3-phase motor at full load is measured by two wattmeter connected at lines A & C. What are the reading in kw? A. 66.23 & 21.655 C. 87.76 & 11. B. 69.5 & 18.26 D. 67.89 & 34.
  3. What will be the rating of a phase advancing plant in kVA if it improves the power factor from 0.8 lagging to 0.95 lagging? The consumer load is 500 kW and the current taken by phase advancer lead the supply voltage at a power factor of 0. A. 150kVA C. 175 kVA B. 200kVA D. 250kVA
  4. A single-phase transformer operates from a 240-V supply. It has an equivalent resistance of 0.1 and an equivalent leakage reactance of 0.5  referred to the primary. The secondary is connected to a coil having a resistance of 200 V and a reactance of 100 . Calculate the secondary terminal voltage. The secondary winding has four times as many turns as the primary. A. 800V C. 700V B. 900V D. 600 V
  5. A no. 14 wire ( the smallest allowed in house wiring ) has a diameter of 0.064 inch. Find the cross-sectional area in circular mils A. 5000 C. 4000 B. 4096 D. 3000
  6. A round aluminum bus bar having a cross-section of 0.185 sq. inch and a length of 2.956ft. has a resistance of 207 micro-ohms at 20oC. What is the resistance in ohm per circular mil foot at this temperature of the aluminum bus bar? A. 18.56 C. 16. B. 14.50 D. 19.
  7. A three-phase induction motor takes 3000 W at 80 percent power factor. Two-wattmeter are used to measure the power. Wa and Wc. What is the reading of Wa A. 2000 C. 2150 B. 3000 D. 2500
  8. In a two-phase, three wire system, the phase voltage is 3000V. Calculate the voltage between the outers. If the current in each phase is 50A and the two currents are in quadrature , What is the value of the current in the common wire? A. 4240V, 707A C. 4402V, 707A B. 2404V, 707A D. 4420V, 707 A
  9. The currents in the two phases of a two-phase , three-wire system are 40 and 70 and are in phase with their respective voltages. Calculate the current in the neutral conductor. A. 80.6 A C. 81.6A B. 82.6 A D. 83.7A
  10. A 3300-V/240-V , single-phase transformer , on no load , takes 2 A at power factor 0.25. Determine graphically , or otherwise , the primary current and power factor when the transformer is supplying a load of 60 A at power factor 0.9 drops A. 5.43A, 1.0. C 4.43A, 1. B. 4.34A, 1.1 D. 3.44A,1.
  11. The armature a dc motor has 648 conductors, 65% of which are directly under the pole where the flux density is 48,000 lines per in^2. If the core diameter is 7 inches and its length is 4 inches and the current in each conductor is 20 Amp. What is the torque exerted in the armature in lb-ft? A. 41.8 C. 120. B. 143 D. 133.
  1. A motor has a nameplate rating of 15hp and 1160 rpm. Solve for the rated torque? A. 103.6 lb-ft C. 121.4 lb-ft B. 67.8 lb-ft D. 123.3 lb-ft
  2. A current supplied by transformer is represented by its equation 10 sin (t + 30 deg) and 5 sin (t + 30 deg). The magnitudes of the components are instantaneous values. What is the RMS value of the current? A. 13.22 amperes C. 1.1 amperes B. 7.9 amperes D. 10.6 amperes
  3. A 50-Hz, three-phase, core-type transformer is connected star-delta and has a line voltage ratio of 11000/415 V. The cross-section of the core is square with a circumscribing circle of 0.6 m diameter. If the maximum flux density is about 1.2T. Calculate the number of turns per phase on both low-voltage and high-voltage windings. Assume the insulation to occupy 10 percent of the gross core. A. 9.87 C. 10.87. B. 8.78 D. 7. GOOD LUCK !!!