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# Electrical Principles for the Electrical Trades Volume 2 Jim Jenneson 6th Edition- Test Bank

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Electrical Principles for the Electrical Trades Volume 2 Jim Jenneson 6th Edition- Test Bank

Sample Questions

Chapter 02

Student: ___________________________________________________________________________

1. What is the principle upon which transformer operation is based?

 A. Lenz’s law

 B. Kirchoff’s current law

 C. Ohm’s law

 D. mutual induction

2. What is the name of the transformer winding that is connected to the electrical supply?

 A. primary

 B. secondary

 C. tertiary

 D. armature

3. What is the name of the transformer winding that is connected to the electrical load?

 A. primary

 B. secondary

 C. tertiary

 D. armature

4. What is the phase difference between the magnetising component of no-load current and the primary voltage?

 A. 0oE

 C. 90oE lagging

 D. 180oE

5. What is the phase difference between the energy component of no-load current and the primary voltage?

 A. 0oE

 C. 90oE lagging

 D. 180oE

6. The phasor addition of which two currents results in the primary current?

 A. Io and Ie

 B. I2 and Io

 C. Io and I1‘

 D. I2 and I1‘

7. What voltage would be induced in a 500 turn coil if it is subjected to a maximum flux of 20 mWb at a frequency of 50 Hz?

 A. 2220 V

 B. 500 V

 C. 500 kV

 D. 2.22 MV

8. Which of the following does not occur when a secondary current flows in a transformer?

 A. A demagnetising flux is produced by the secondary current.

 B. The self-induced primary voltage decreases.

 C. The primary current increases.

 D. The mutual flux changes from the no-load value.

9. What is the secondary voltage of a transformer that has 1000 primary turns and 100 secondary turns when it is connected to a 230 V supply?

 A. 2300 V

 B. 230 V

 C. 23 V

 D. 2.3 V

10. What is the primary voltage of a transformer that has 250 primary turns and 50 secondary turns when a voltage of 12 V is measured across the secondary terminals?

 A. 60 V

 B. 2.4 V

 C. 24 V

 D. 240 V

11. What is the secondary current of a transformer that has 450 primary turns and 25 secondary turns when it draws a current of 4 A from the supply?

 A. 4 A

 B. 72 A

 C. 222 mA

 D. 25 A

12. What is the secondary current of a 230 V / 110 V transformer that draws a current of 0.5 A from the supply?

 A. 239 mA

 B. 500 mA

 C. 1045 mA

 D. 2186 mA

13. What is the primary current of a transformer that has 800 primary turns and 100 secondary turns when a 12 Ω resistive load is connected to the 24 V secondary winding?

 A. 250 mA

 B. 1.5 A

 C. 3 A

 D. 4 A

14. What is the primary winding impedance of a 240 V/ 12 V transformer that has a secondary winding impedance of 2.88Ω?

 A. 7.2 mΩ

 B. 0.144 Ω

 C. 57.6 Ω

 D. 1152 Ω

15. Circulating currents in a transformer core are known as:

 A. hysteresis

 B. reflected currents

 C. Kirchoff currents

 D. eddy currents

16. The efficiency of a transformer can be calculated by:

 A. output/input

 B. input/output

 C. output/(input + losses)

 D. output/( output – losses)

17. Hysteresis and eddy current losses are collectively known as:

 A. copper losses

 B. iron losses

 C. variable losses

18. Which test may be used to determine the fixed losses of a transformer?

 A. open-circuit test

 B. short circuit test

 C. continuity test

 D. insulation resistance test

19. Flux leakage in a transformer core causes:

 A. increased terminal voltage

 B. increased secondary current

 C. increased inductive reactance

 D. increased primary voltage

20. What is the full load secondary voltage of a 400 V / 110 V transformer that has a voltage regulation of 3 %?

 A. 107.0 V

 B. 106.7 V

 C. 106.8 V

 D. 113.3 V

21. Which of the following is not a type of transformer core?

 A. pancake

 B. core

 C. shell

 D. toroidal

22. Which of the following transformer core types results in a shorter, constant cross-section magnetic path with very low flux leakage?

 A. pancake

 B. core

 C. shell

 D. toroidal

23. Which of the following factors does not influence the arrangement of transformer windings?

 A. core type

 B. intended use

 C. eddy currents

 D. supply frequency

24. What is the main benefit of using a cruciform transformer core?

 A. It is relatively inexpensive.

 B. It overcomes the tendency for unequal flux densities.

 C. Large cross-sectional area windings are wound onto a circular core.

 D. A number of different sized laminations are required.

25. Transformers are rated based on:

 A. input power

 B. output power

 C. losses

 D. efficiency

26. Ambient temperature has an effect on:

 A. induced magnetic flux

 B. the magnetising component of no-load current

 C. winding current rating

 D. magnetic core selection

27. If a 400 V / 110 V transformer supplies its full load of 10 A at 0.88 lagging power factor, what is the transformer’s rating?

 A. 3520 W

 B. 4000 VA

 C. 968 W

 D. 1100 VA

28. Why are transformer tanks usually painted in low sheen variations of black, green or grey?

 A. to match supply authority corporate colours

 B. to enable lower oil temperatures

 C. to camouflage the transformers

 D. to reduce iron losses

29. Which of the following is not a suitable method for cooling transformers?

 A. water cooling

 B. oil cooling

 C. air cooling

 D. refrigeration

30. Which of the following methods can be used to circulate coolant around a transformer tank?

 A. induction

 C. conduction

 D. convection

31. Which of the following labels would indicate the start of the secondary winding of a transformer?

 A. A1

 B. A2

 C. a1

 D. a2

32. What phase shift would occur for a delta–star connected supply transformer?

 A. V2 lags V1 by 30oE.

 B. V2 leads V1 by 30oE.

 C. V2 lags V1 by 180oE.

 D. V2 and V1 are in phase.

33. What method is typically used to adjust the voltage at the load end of a long transmission line without interrupting the supply?

 C. off-load tap changing at the supply end

 D. on-load tap changing at the supply end

34. If a delta–star connected 600 V three-phase transformer has 450 turns per phase on the primary windings and 15 turns on the secondaries, what is the output line voltage?

 A. 11.5 V

 B. 20 V

 C. 34.6 V

 D. 41.5 V

35. Which of the following is not a requirement for paralleling transformers?

 A. equal voltages

 B. same phase sequence

 C. opposite phase angle shift

 D. compatible internal impedance

36. What type of transformer connection requires a reduction to 58% capacity?

 A. open delta connection

 B. delta–star connection

 C. star–delta connection

 D. open star connection

37. If a voltmeter reading of double the line voltage is obtained between the open ends of delta connected parallel transformers it means that:

 A. The transformers are correctly connected.

 B. The transformers must be reconnected in star.

 C. One of the windings has been reversed.

 D. Two of the windings have been interchanged.

38. What type of transformer is required for metering of an installation with a maximum demand of 200 A per phase?

 A. a potential transformer

 B. a current transformer

 C. an autotransformer

 D. a high reactance transformer

39. What type of transformer is limited to a secondary voltage of + or – 25% of the primary voltage?

 A. an instrument transformer

 B. an isolation transformer

 C. an autotransformer

 D. a high reactance transformer

40. What is the main purpose of magnetic shunts in a welding transformer?

 A. to control the secondary current

 B. to reduce leakage flux

 C. to increase the secondary voltage

 D. to improve the power factor

Chapter 02 Key

1. What is the principle upon which transformer operation is based?

 A. Lenz’s law

 B. Kirchoff’s current law

 C. Ohm’s law

 D. mutual induction

 Difficulty: Easy EPC 23, 24, 25, 26, 40 Jenneson chapter 2 KS01-EG006A T2

2. What is the name of the transformer winding that is connected to the electrical supply?

 A. primary

 B. secondary

 C. tertiary

 D. armature

 Difficulty: Easy EPC 23, 24, 25, 26, 40 Jenneson chapter 2 KS01-EG006A T2

3. What is the name of the transformer winding that is connected to the electrical load?

 A. primary

 B. secondary

 C. tertiary

 D. armature

 Difficulty: Easy EPC 23, 24, 25, 26, 40 Jenneson chapter 2 KS01-EG006A T2

4. What is the phase difference between the magnetising component of no-load current and the primary voltage?

 A. 0oE

 C. 90oE lagging

 D. 180oE

 Difficulty: Medium EPC 23, 24, 25, 26, 40 Jenneson chapter 2 KS01-EG006A T2

5. What is the phase difference between the energy component of no-load current and the primary voltage?

 A. 0oE

 C. 90oE lagging

 D. 180oE

 Difficulty: Medium EPC 23, 24, 25, 26, 40 Jenneson chapter 2 KS01-EG006A T2

6. The phasor addition of which two currents results in the primary current?

 A. Io and Ie

 B. I2 and Io

 C. Io and I1‘

 D. I2 and I1‘

 Difficulty: Medium EPC 23, 24, 25, 26, 40 Jenneson chapter 2 KS01-EG006A T2

7. What voltage would be induced in a 500 turn coil if it is subjected to a maximum flux of 20 mWb at a frequency of 50 Hz?

 A. 2220 V

 B. 500 V

 C. 500 kV

 D. 2.22 MV

 Difficulty: Medium EPC 23, 24, 25, 26, 40 Jenneson chapter 2 KS01-EG006A T2

8. Which of the following does not occur when a secondary current flows in a transformer?

 A. A demagnetising flux is produced by the secondary current.

 B. The self-induced primary voltage decreases.

 C. The primary current increases.

 D. The mutual flux changes from the no-load value.

 Difficulty: Hard EPC 23, 24, 25, 26, 40 Jenneson chapter 2 KS01-EG006A T2

9. What is the secondary voltage of a transformer that has 1000 primary turns and 100 secondary turns when it is connected to a 230 V supply?

 A. 2300 V

 B. 230 V

 C. 23 V

 D. 2.3 V

 Difficulty: Easy EPC 23, 24, 25, 26, 40 Jenneson chapter 2 KS01-EG006A T2

10. What is the primary voltage of a transformer that has 250 primary turns and 50 secondary turns when a voltage of 12 V is measured across the secondary terminals?

 A. 60 V

 B. 2.4 V

 C. 24 V

 D. 240 V

 Difficulty: Easy EPC 23, 24, 25, 26, 40 Jenneson chapter 2 KS01-EG006A T2

Chapter 04

Student: ___________________________________________________________________________

1. Which two forms of energy does a DC machine convert between?

 A. kinetic and chemical

 B. electrical and kinetic

 C. kinetic and acoustic

 D. acoustic and chemical

2. From what material are commutator segments made?

 A. copper

 B. iron

 C. silicon steel

 D. mica

3. What is the main purpose of the commutator in a compound connected DC generator?

 A. to connect the field to the supply

 B. to connect the armature to the field

 C. to convert generated AC to a DC supply

 D. to convert DC to AC

4. Which of the following is not an essential requirement for generation of an EMF?

 A. conductor

 B. electric field

 C. magnetic field

 D. relative motion

5. Which of the following is not a typical part of a DC machine?

 A. yoke

 B. brush gear

 C. armature

 D. rotor

6. What is the main reason for shaping field poles?

 A. to hold the field coils in position

 B. to assist in assembly of the DC machine

 C. to permit a greater area in the flux path close to the armature

 D. to increase the magnetic reluctance of the air gap

7. Which type of DC generator has a linear voltage/speed characteristic?

 A. shunt-connected

 B. series-connected

 C. compound connected

 D. permanent magnet

8. Which type of DC generator is impractical and therefore not used?

 A. shunt-connected

 B. series-connected

 C. compound connected

 D. permanent magnet

9. In which type of DC generator is the field current independent of the speed of the prime mover?

 A. separately excited

 B. permanent magnet

 C. shunt-connected

 D. series-connected

10. What is the value of generated voltage in a 4-pole, wave wound armature that has 500 conductors and 30 mWb of flux per pole when it rotates at 1200 RPM?

 A. 300 kV

 B. 600 kV

 C. 600 V

 D. 300 V

11. Which type of DC generator is safe to operate with a short circuited load?

 A. shunt-connected

 B. separately excited

 C. cumulatively compounded

 D. differentially compounded

12. How is voltage control usually achieved for a shunt-connected DC generator?

 A. magnetic shunt

 B. resistor connected in series with the field

 C. resistor connected in shunt with the field

 D. changing the number of poles

13. Which type of DC generator has a series field connected to reinforce the shunt field?

 A. shunt-connected

 B. separately excited

 C. cumulatively compounded

 D. differentially compounded

14. Which of the following describes the performance of an over-compounded DC generator on load?

 A. As the load current increases the terminal voltage decreases.

 B. As the load current increases the terminal voltage increases.

 C. As the speed increases the terminal voltage decreases.

 D. As the speed decreases the load current increases.

15. What is the rated full load voltage for a compound DC generator that has a no load voltage of 750 V and a voltage regulation of 3%?

 A. 728.2 V

 B. 727.5 V

 C. 22.5 V

 D. 772.5 V

16. The interaction of the magnetic field around the armature and the main field of a DC motor is the basis of:

 A. back EMF

 B. electromagnetic induction

 C. the piezoelectric effect

 D. motor action

17. What is the most common type of DC motor?

 A. shunt-connected

 B. series-connected

 C. compound connected

 D. permanent magnet

18. Which connections must be reversed to reverse the direction of rotation of a DC motor?

 A. the supply terminals

 B. the armature connections

 C. the interpole connections

 D. one field connection

19. What is the back EMF for a DC motor operating with the following specifications: armature circuit resistance = 0.01 Ω; terminal voltage = 200 V; armature current = 50 A?

 A. 199.5 V

 B. 200.5 V

 C. 10 V

 D. 52 V

20. Which type of DC motor will exhibit a wide variation in speed based on the driven load?

 A. separately excited

 B. shunt-connected

 C. series-connected

 D. compound connected

21. What is the main purpose of interpoles?

 A. to reduce back EMF

 B. to improve commutation

 C. to strengthen the armature field

 D. to reduce hysteresis

22. What is the torque produced by a 4-pole, wave wound DC motor if it has 50 conductors, 40 mWb of flux per pole and an armature current of 32 A when it is operating at 1200 RPM?

 A. 10.19 Nm

 B. 710.40 Nm

 C. 15.28 Nm

 D. 20.37 Nm

23. What is the rated full load speed for a DC motor that has a no-load speed of 1300 RPM and a speed regulation of 5%?

 A. 1235 RPM

 B. 1238 RPM

 C. 1262 RPM

 D. 1265 RPM

24. What torque is produced by a 2.6 kW, 8-pole, lap wound DC motor when it is rotating at 1400 RPM?

 A. 17.73 Nm

 B. 141.88 Nm

 C. 381 kNm

 D. 34.46 Nm

25. Which type of DC machine loss is almost constant from no load to full load?

 A. copper losses

 B. friction

 C. iron losses

 D. windage

26. What is the terminal voltage of a compound DC generator given the following data: load current = 43 A; series field resistance = 0.15 Ω; armature resistance = 0.1 Ω; shunt field resistance = 200 Ω; generated voltage = 420 V?

 A. 408.73 V

 B. 409.78 V

 C. 430.75 V

 D. 409.25 V

27. What is the back EMF of a 110 V shunt-connected motor if it draws 18 A from the supply, the armature resistance is 0.3 Ω and the field current is 0.8 A?

 A. 104.60 V

 B. 104.84 V

 C. 115.16 V

 D. 115.40 V

28. What is the efficiency of a DC generator with the following specifications: load current = 27 A; terminal voltage = 300 V; total losses = 965 W?

 A. 78.71%

 B. 88.09%

 C. 89.35%

 D. 90.62%

29. A 250 V DC long shunt compound motor has the following specifications: full load current = 54 A; series field resistance = 0.25 Ω; armature resistance = 0.05 Ω; shunt field resistance = 100 Ω; iron and stray losses = 680 W. What is this motor’s efficiency?

 A. 83.85%

 B. 84.44%

 C. 89.47%

 D. 94.96%

30. Which of the following is not a factor that opposes ideal commutation?

 A. coil self-inductance

 B. armature reaction

 C. back EMF

 D. irregularities in the commutator surface

31. Which of the following methods can be used to overcome the effects of coil self-inductance?

 A. interpoles

 B. compensating windings

 C. lower resistance brushes

 D. shifting the brush position

32. Which of the following is a problem caused by sparking brushes?

 A. burnt edges of commutator bars

 B. shifting of the magnetic axis

 C. coil self-inductance

 D. increased back EMF

33. When is sparking at the commutator likely to occur?

 A. when the brush is in contact with only one commutator segment

 B. when the brush contact changes from contact with one segment to contact with two segments

 C. when the brush is in contact with two commutator segments

 D. when the brush contact changes from contact with two segments to contact with one segment

34. What is the main effect of armature reaction?

 A. improved commutation

 B. shifting of the magnetic axis

 C. coil self-inductance

 D. increased back EMF

35. Which of the following is not a method of correction of armature reaction?

 A. interpoles

 B. compensating windings

 C. higher resistance brushes

 D. shifting the brush position

36. Which of the following is the most effective method for correction of armature reaction for rapidly fluctuating loads?

 A. interpoles

 B. compensating windings

 C. higher resistance brushes

 D. shifting the brush position

37. Which type of DC motor can be remotely controlled by providing negative feedback?

 A. brushless DC motor

 B. printed circuit motor

 C. servo motor

 D. stepper motor

38. Which of the following is not an advantage of servo motors?

 A. higher output torque

 B. high efficiency

 C. low input current

 D. low stability

39. What aspect of printed circuit motors allows for more evenly distributed armature windings?

 A. air core

 B. iron core

 C. copper windings

 D. etched windings

40. Which type of DC motor has a toothed rotor and toothed poles?

 A. brushless DC motor

 B. printed circuit motor

 C. permanent magnet motor

 D. four-phase stepper motor

Chapter 04 Key

1. Which two forms of energy does a DC machine convert between?

 A. kinetic and chemical

 B. electrical and kinetic

 C. kinetic and acoustic

 D. acoustic and chemical

 Difficulty: Easy EPC 8, 9, 40 Jenneson chapter 4 KS01-EG101A T8

2. From what material are commutator segments made?

 A. copper

 B. iron

 C. silicon steel

 D. mica

 Difficulty: Easy EPC 8, 9, 40 Jenneson chapter 4 KS01-EG101A T8 KS01-EG101A T9

3. What is the main purpose of the commutator in a compound connected DC generator?

 A. to connect the field to the supply

 B. to connect the armature to the field

 C. to convert generated AC to a DC supply

 D. to convert DC to AC

 Difficulty: Medium EPC 8, 9, 40 Jenneson chapter 4 KS01-EG101A T8

4. Which of the following is not an essential requirement for generation of an EMF?

 A. conductor

 B. electric field

 C. magnetic field

 D. relative motion

 Difficulty: Medium EPC 8, 9, 40 Jenneson chapter 4 KS01-EG101A T10 KS01-EG101A T8

5. Which of the following is not a typical part of a DC machine?

 A. yoke

 B. brush gear

 C. armature

 D. rotor

 Difficulty: Hard EPC 8, 9, 40 Jenneson chapter 4 KS01-EG101A T9

6. What is the main reason for shaping field poles?

 A. to hold the field coils in position

 B. to assist in assembly of the DC machine

 C. to permit a greater area in the flux path close to the armature

 D. to increase the magnetic reluctance of the air gap

 Difficulty: Hard EPC 8, 9, 40 Jenneson chapter 4 KS01-EG101A T8 KS01-EG101A T9

7. Which type of DC generator has a linear voltage/speed characteristic?

 A. shunt-connected

 B. series-connected

 C. compound connected

 D. permanent magnet

 Difficulty: Easy EPC 8, 9, 40 Jenneson chapter 4 KS01-EG101A T10

8. Which type of DC generator is impractical and therefore not used?

 A. shunt-connected

 B. series-connected

 C. compound connected

 D. permanent magnet

 Difficulty: Easy EPC 8, 9, 40 Jenneson chapter 4 KS01-EG101A T10

9. In which type of DC generator is the field current independent of the speed of the prime mover?

 A. separately excited

 B. permanent magnet

 C. shunt-connected

 D. series-connected

 Difficulty: Easy EPC 8, 9, 40 Jenneson chapter 4 KS01-EG101A T10

10. What is the value of generated voltage in a 4-pole, wave wound armature that has 500 conductors and 30 mWb of flux per pole when it rotates at 1200 RPM?

 A. 300 kV

 B. 600 kV

 C. 600 V

 D. 300 V

 Difficulty: Medium EPC 8, 9, 40 Jenneson chapter 4 KS01-EG101A T10

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