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Electrical Principles for the Electrical Trades Volume 2 Jim Jenneson 6th Edition- Test Bank
Sample Questions
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Chapter 02
Student: ___________________________________________________________________________
| 1. |
What is the principle upon which transformer operation is based?
| B. |
Kirchoff’s current law |
|
| 2. |
What is the name of the transformer winding that is connected to the electrical supply?
|
| 3. |
What is the name of the transformer winding that is connected to the electrical load?
|
| 4. |
What is the phase difference between the magnetising component of no-load current and the primary voltage?
|
| 5. |
What is the phase difference between the energy component of no-load current and the primary voltage?
|
| 6. |
The phasor addition of which two currents results in the primary current?
|
| 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?
|
| 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?
|
| 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?
|
| 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?
|
| 12. |
What is the secondary current of a 230 V / 110 V transformer that draws a current of 0.5 A from the supply?
|
| 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?
|
| 14. |
What is the primary winding impedance of a 240 V/ 12 V transformer that has a secondary winding impedance of 2.88Ω?
|
| 15. |
Circulating currents in a transformer core are known as:
|
| 16. |
The efficiency of a transformer can be calculated by:
| C. |
output/(input + losses) |
| D. |
output/( output – losses) |
|
| 17. |
Hysteresis and eddy current losses are collectively known as:
|
| 18. |
Which test may be used to determine the fixed losses of a transformer?
| 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 %?
|
| 21. |
Which of the following is not a type of transformer core?
|
| 22. |
Which of the following transformer core types results in a shorter, constant cross-section magnetic path with very low flux leakage?
|
| 23. |
Which of the following factors does not influence the arrangement of transformer windings?
|
| 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:
|
| 26. |
Ambient temperature has an effect on:
| 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?
|
| 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 |
|
| 29. |
Which of the following is not a suitable method for cooling transformers?
|
| 30. |
Which of the following methods can be used to circulate coolant around a transformer tank?
|
| 31. |
Which of the following labels would indicate the start of the secondary winding of a transformer?
|
| 32. |
What phase shift would occur for a delta–star connected supply transformer?
| 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?
| A. |
off-load tap changing at the load end |
| B. |
on-load tap changing at the load end |
| 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?
|
| 35. |
Which of the following is not a requirement for paralleling transformers?
| C. |
opposite phase angle shift |
| D. |
compatible internal impedance |
|
| 36. |
What type of transformer connection requires a reduction to 58% capacity?
|
| 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 |
| 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 |
| 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?
| B. |
Kirchoff’s current law |
|
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?
|
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?
|
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?
|
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?
|
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?
|
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?
|
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?
|
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?
|
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?
| B. |
electrical and kinetic |
|
| 2. |
From what material are commutator segments made?
|
| 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 |
|
| 4. |
Which of the following is not an essential requirement for generation of an EMF?
|
| 5. |
Which of the following is not a typical part of a DC machine?
|
| 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?
|
| 8. |
Which type of DC generator is impractical and therefore not used?
|
| 9. |
In which type of DC generator is the field current independent of the speed of the prime mover?
|
| 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?
|
| 11. |
Which type of DC generator is safe to operate with a short circuited load?
| C. |
cumulatively compounded |
| D. |
differentially compounded |
|
| 12. |
How is voltage control usually achieved for a shunt-connected DC generator?
| 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?
| 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%?
|
| 16. |
The interaction of the magnetic field around the armature and the main field of a DC motor is the basis of:
| B. |
electromagnetic induction |
| C. |
the piezoelectric effect |
|
| 17. |
What is the most common type of DC motor?
|
| 18. |
Which connections must be reversed to reverse the direction of rotation of a DC motor?
| B. |
the armature connections |
| C. |
the interpole connections |
|
| 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?
|
| 20. |
Which type of DC motor will exhibit a wide variation in speed based on the driven load?
|
| 21. |
What is the main purpose of interpoles?
| B. |
to improve commutation |
| C. |
to strengthen the armature field |
|
| 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?
|
| 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%?
|
| 24. |
What torque is produced by a 2.6 kW, 8-pole, lap wound DC motor when it is rotating at 1400 RPM?
|
| 25. |
Which type of DC machine loss is almost constant from no load to full load?
|
| 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?
|
| 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?
|
| 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?
|
| 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?
|
| 30. |
Which of the following is not a factor that opposes ideal commutation?
| D. |
irregularities in the commutator surface |
|
| 31. |
Which of the following methods can be used to overcome the effects of coil self-inductance?
| 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 |
|
| 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?
| B. |
shifting of the magnetic axis |
|
| 35. |
Which of the following is not a method of correction of armature reaction?
| 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?
| C. |
higher resistance brushes |
| D. |
shifting the brush position |
|
| 37. |
Which type of DC motor can be remotely controlled by providing negative feedback?
|
| 38. |
Which of the following is not an advantage of servo motors?
|
| 39. |
What aspect of printed circuit motors allows for more evenly distributed armature windings?
|
| 40. |
Which type of DC motor has a toothed rotor and toothed poles?
| C. |
permanent magnet motor |
| D. |
four-phase stepper motor |
|
Chapter 04 Key
| 1. |
Which two forms of energy does a DC machine convert between?
| B. |
electrical and kinetic |
|
Difficulty: Easy
EPC 8, 9, 40
Jenneson chapter 4
KS01-EG101A T8
|
| 2. |
From what material are commutator segments made?
|
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 |
|
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?
|
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?
|
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?
|
Difficulty: Easy
EPC 8, 9, 40
Jenneson chapter 4
KS01-EG101A T10
|
| 8. |
Which type of DC generator is impractical and therefore not used?
|
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?
|
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?
|
Difficulty: Medium
EPC 8, 9, 40
Jenneson chapter 4
KS01-EG101A T10
|
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