BCIT Electrical DC Machines Level 3
Exam Updated Actual Questions and
Correct Answers
Section 1: DC Generator Fundamentals
Question 1
What is the main difference in the construction of a DC generator and
a DC motor?
A. Type of armature windings
B. Type of field poles
C. Type of enclosure
D. Type of commutator
Correct Answer: A
Rationale: DC generators and motors share the same basic physical
construction. The fundamental difference lies in their operation and
the type of armature windings used, which are optimized for their
specific function.
Question 2
What is the electrical function of the commutator?
,A. To reverse armature connections to maintain unidirectional current
in the external circuit
B. To increase the voltage output
C. To reduce sparking at the brushes
D. To convert mechanical energy into electrical energy
Correct Answer: A
Rationale: The commutator is the component that converts the
alternating current (AC) induced in the armature into direct current
(DC) for the external circuit. It achieves this by reversing the armature
connections at the appropriate times during rotation.
Question 3
What are the three basic types of armature windings?
A. Series, shunt, and compound
B. Lap, wave, and frog-leg
C. Closed, open, and parallel
D. Progressive, retrogressive, and concentric
Correct Answer: B
Rationale: The three basic types of armature windings are lap-wound,
wave-wound, and frog-leg-wound. Lap-wound armatures are used in
high-current, low-voltage applications, while wave-wound armatures
are used in high-voltage, low-current applications.
Question 4
Which armature winding is used in high-current, low-voltage
applications?
,A. Series
B. Lap
C. Wave
D. Compound
Correct Answer: B
Rationale: Lap-wound armatures are used in high-current, low-voltage
applications. They are typically constructed with a larger gauge wire
and provide parallel paths for current flow.
Question 5
Which of the following is a common brush material used in DC
machines?
A. Carbon
B. Graphite
C. Copper-carbon alloy
D. All of the above
Correct Answer: D
Rationale: DC machines commonly use carbon, graphite, or
copper-carbon alloy brushes. The choice of brush material depends
on the specific application and the operating conditions of the
machine.
Question 6
Suitable brush pressure is usually between:
, A. 0.5 and 1 psi
B. 1 and 2 psi
C. 2 and 3 psi
D. 3 and 4 psi
Correct Answer: B
Rationale: Proper brush pressure is essential for efficient
commutation and to prevent excessive sparking. The suitable brush
pressure for DC machines is generally between 1 and 2 pounds per
square inch (psi).
Question 7
What is the function of field poles in a DC machine?
A. To support the brushes
B. To produce the magnetic field required for operation
C. To connect the armature to the external circuit
D. To provide mechanical support for the machine
Correct Answer: B
Rationale: The field poles are responsible for producing the magnetic
field required for the operation of the DC machine. They are made of
soft iron or silicon steel and carry the field windings.
Question 8
Small generators that use permanent magnets for field excitation are
called:
Exam Updated Actual Questions and
Correct Answers
Section 1: DC Generator Fundamentals
Question 1
What is the main difference in the construction of a DC generator and
a DC motor?
A. Type of armature windings
B. Type of field poles
C. Type of enclosure
D. Type of commutator
Correct Answer: A
Rationale: DC generators and motors share the same basic physical
construction. The fundamental difference lies in their operation and
the type of armature windings used, which are optimized for their
specific function.
Question 2
What is the electrical function of the commutator?
,A. To reverse armature connections to maintain unidirectional current
in the external circuit
B. To increase the voltage output
C. To reduce sparking at the brushes
D. To convert mechanical energy into electrical energy
Correct Answer: A
Rationale: The commutator is the component that converts the
alternating current (AC) induced in the armature into direct current
(DC) for the external circuit. It achieves this by reversing the armature
connections at the appropriate times during rotation.
Question 3
What are the three basic types of armature windings?
A. Series, shunt, and compound
B. Lap, wave, and frog-leg
C. Closed, open, and parallel
D. Progressive, retrogressive, and concentric
Correct Answer: B
Rationale: The three basic types of armature windings are lap-wound,
wave-wound, and frog-leg-wound. Lap-wound armatures are used in
high-current, low-voltage applications, while wave-wound armatures
are used in high-voltage, low-current applications.
Question 4
Which armature winding is used in high-current, low-voltage
applications?
,A. Series
B. Lap
C. Wave
D. Compound
Correct Answer: B
Rationale: Lap-wound armatures are used in high-current, low-voltage
applications. They are typically constructed with a larger gauge wire
and provide parallel paths for current flow.
Question 5
Which of the following is a common brush material used in DC
machines?
A. Carbon
B. Graphite
C. Copper-carbon alloy
D. All of the above
Correct Answer: D
Rationale: DC machines commonly use carbon, graphite, or
copper-carbon alloy brushes. The choice of brush material depends
on the specific application and the operating conditions of the
machine.
Question 6
Suitable brush pressure is usually between:
, A. 0.5 and 1 psi
B. 1 and 2 psi
C. 2 and 3 psi
D. 3 and 4 psi
Correct Answer: B
Rationale: Proper brush pressure is essential for efficient
commutation and to prevent excessive sparking. The suitable brush
pressure for DC machines is generally between 1 and 2 pounds per
square inch (psi).
Question 7
What is the function of field poles in a DC machine?
A. To support the brushes
B. To produce the magnetic field required for operation
C. To connect the armature to the external circuit
D. To provide mechanical support for the machine
Correct Answer: B
Rationale: The field poles are responsible for producing the magnetic
field required for the operation of the DC machine. They are made of
soft iron or silicon steel and carry the field windings.
Question 8
Small generators that use permanent magnets for field excitation are
called:
