Oregon Electrical and Computer
Engineering Exam Practice Questions
And Correct Answers (Verified Answers)
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1. An electrical engineer is designing a three-phase industrial distribution
system in which the balanced load is connected in a wye
configuration. If the line-to-line voltage is 480 V, what is the
approximate line-to-neutral voltage for a balanced system?
A. 120 V
B. 277 V
C. 339 V
D. 480 V
For a balanced wye system, the line-to-neutral voltage equals the line-to-
line voltage divided by 3\sqrt{3}. Thus, 480/3≈277480/\sqrt{3}\approx277
V.
2. A balanced three-phase load draws 50 A at 480 V with a power factor
of 0.8 lagging. Approximately how much real power does the load
consume?
A. 19.2 kW
B. 24.0 kW
,C. 33.3 kW
D. 38.4 kW
Three-phase real power is P=3VLILcosϕP=\sqrt{3}V_LI_L\cos\phi.
Substituting the given values gives approximately
1.732(480)(50)(0.8)=33.31.732(480)(50)(0.8)=33.3 kW.
3. An industrial facility has a large inductive load that operates at a
lagging power factor of 0.70. What is the principal reason for installing
appropriately sized power-factor correction capacitors?
A. Increase system frequency
B. Increase conductor resistance
C. Reduce reactive current drawn from the supply and improve power
factor
D. Convert three-phase power into direct current
Capacitors supply leading reactive power that offsets part of the inductive
reactive demand. This reduces reactive current from the source and can
reduce losses and voltage drop while improving the facility's power factor.
4. A transformer has 2,400 primary turns and 240 secondary turns. If the
primary is supplied with 4,800 V AC, what is the ideal secondary
voltage?
A. 24 V
B. 480 V
C. 2,400 V
D. 48,000 V
For an ideal transformer, the voltage ratio equals the turns ratio. The
secondary voltage is 4,800(240/2,400)=4804,800(240/2,400)=480 V.
5. A transformer supplying a sensitive electronic load experiences a
significant voltage reduction when the load increases. Which
transformer characteristic most directly describes the difference
between no-load and loaded secondary voltage?
,A. Hysteresis loss
B. Transformer frequency
C. Voltage regulation
D. Dielectric strength
Transformer voltage regulation describes the change in secondary terminal
voltage between specified load conditions, commonly from no-load to full-
load operation. Poor regulation produces larger voltage changes as
loading varies.
6. A 60-Hz transformer core is operated at a substantially higher
frequency while maintaining the same applied voltage and number of
turns. What is the principal concern?
A. Core flux necessarily decreases to zero
B. The relationship between voltage, frequency, turns, and core flux
changes, potentially affecting core losses and operating limits
C. The transformer becomes a resistor
D. The secondary voltage becomes independent of turns ratio
Transformer core flux is related to applied voltage, frequency, and number
of turns. Changing frequency without appropriately considering voltage
and flux can alter magnetic operating conditions and losses.
7. Which semiconductor device is specifically designed to control large
currents and is commonly used as a power switch in converters and
motor drives?
A. Small-signal diode only
B. IGBT
C. Thermistor
D. Photodiode
An insulated-gate bipolar transistor, or IGBT, combines voltage-controlled
gate characteristics with bipolar conduction characteristics and is widely
used for high-power switching applications such as variable-frequency
drives and inverters.
, 8. A silicon diode is forward biased in a conventional low-voltage power
circuit. Which behavior is expected once the applied voltage is
sufficient to establish substantial forward conduction?
A. It blocks all current indefinitely
B. It permits current primarily in the forward direction
C. It converts AC directly into mechanical energy
D. It produces an open circuit regardless of voltage
A conventional diode conducts predominantly in the forward direction
once its forward-bias conditions are sufficient and blocks current in reverse
bias within its rated limits.
9. A full-wave bridge rectifier is connected to a sinusoidal AC source.
What is its primary function?
A. Increase the source frequency by mechanical means
B. Convert AC voltage into a pulsating DC voltage
C. Convert DC voltage into three-phase AC
D. Maintain a constant resistance
A bridge rectifier uses four diodes to conduct during both half-cycles of an
AC source, producing a full-wave pulsating DC output that can
subsequently be filtered and regulated.
10. A capacitor is placed across the output of a rectifier to reduce
voltage ripple. What occurs during normal operation?
A. The capacitor discharges only when the source voltage is maximum
B. The capacitor charges near voltage peaks and supplies current to the
load between peaks
C. The capacitor eliminates all load current
D. The capacitor converts DC into a pure sine wave
A smoothing capacitor charges when the rectified voltage rises above its
stored voltage and discharges into the load as the source voltage falls. This
reduces the magnitude of output voltage ripple.
Engineering Exam Practice Questions
And Correct Answers (Verified Answers)
Plus Rationale 2027 Q&A| Instant
Download Pdf.
1. An electrical engineer is designing a three-phase industrial distribution
system in which the balanced load is connected in a wye
configuration. If the line-to-line voltage is 480 V, what is the
approximate line-to-neutral voltage for a balanced system?
A. 120 V
B. 277 V
C. 339 V
D. 480 V
For a balanced wye system, the line-to-neutral voltage equals the line-to-
line voltage divided by 3\sqrt{3}. Thus, 480/3≈277480/\sqrt{3}\approx277
V.
2. A balanced three-phase load draws 50 A at 480 V with a power factor
of 0.8 lagging. Approximately how much real power does the load
consume?
A. 19.2 kW
B. 24.0 kW
,C. 33.3 kW
D. 38.4 kW
Three-phase real power is P=3VLILcosϕP=\sqrt{3}V_LI_L\cos\phi.
Substituting the given values gives approximately
1.732(480)(50)(0.8)=33.31.732(480)(50)(0.8)=33.3 kW.
3. An industrial facility has a large inductive load that operates at a
lagging power factor of 0.70. What is the principal reason for installing
appropriately sized power-factor correction capacitors?
A. Increase system frequency
B. Increase conductor resistance
C. Reduce reactive current drawn from the supply and improve power
factor
D. Convert three-phase power into direct current
Capacitors supply leading reactive power that offsets part of the inductive
reactive demand. This reduces reactive current from the source and can
reduce losses and voltage drop while improving the facility's power factor.
4. A transformer has 2,400 primary turns and 240 secondary turns. If the
primary is supplied with 4,800 V AC, what is the ideal secondary
voltage?
A. 24 V
B. 480 V
C. 2,400 V
D. 48,000 V
For an ideal transformer, the voltage ratio equals the turns ratio. The
secondary voltage is 4,800(240/2,400)=4804,800(240/2,400)=480 V.
5. A transformer supplying a sensitive electronic load experiences a
significant voltage reduction when the load increases. Which
transformer characteristic most directly describes the difference
between no-load and loaded secondary voltage?
,A. Hysteresis loss
B. Transformer frequency
C. Voltage regulation
D. Dielectric strength
Transformer voltage regulation describes the change in secondary terminal
voltage between specified load conditions, commonly from no-load to full-
load operation. Poor regulation produces larger voltage changes as
loading varies.
6. A 60-Hz transformer core is operated at a substantially higher
frequency while maintaining the same applied voltage and number of
turns. What is the principal concern?
A. Core flux necessarily decreases to zero
B. The relationship between voltage, frequency, turns, and core flux
changes, potentially affecting core losses and operating limits
C. The transformer becomes a resistor
D. The secondary voltage becomes independent of turns ratio
Transformer core flux is related to applied voltage, frequency, and number
of turns. Changing frequency without appropriately considering voltage
and flux can alter magnetic operating conditions and losses.
7. Which semiconductor device is specifically designed to control large
currents and is commonly used as a power switch in converters and
motor drives?
A. Small-signal diode only
B. IGBT
C. Thermistor
D. Photodiode
An insulated-gate bipolar transistor, or IGBT, combines voltage-controlled
gate characteristics with bipolar conduction characteristics and is widely
used for high-power switching applications such as variable-frequency
drives and inverters.
, 8. A silicon diode is forward biased in a conventional low-voltage power
circuit. Which behavior is expected once the applied voltage is
sufficient to establish substantial forward conduction?
A. It blocks all current indefinitely
B. It permits current primarily in the forward direction
C. It converts AC directly into mechanical energy
D. It produces an open circuit regardless of voltage
A conventional diode conducts predominantly in the forward direction
once its forward-bias conditions are sufficient and blocks current in reverse
bias within its rated limits.
9. A full-wave bridge rectifier is connected to a sinusoidal AC source.
What is its primary function?
A. Increase the source frequency by mechanical means
B. Convert AC voltage into a pulsating DC voltage
C. Convert DC voltage into three-phase AC
D. Maintain a constant resistance
A bridge rectifier uses four diodes to conduct during both half-cycles of an
AC source, producing a full-wave pulsating DC output that can
subsequently be filtered and regulated.
10. A capacitor is placed across the output of a rectifier to reduce
voltage ripple. What occurs during normal operation?
A. The capacitor discharges only when the source voltage is maximum
B. The capacitor charges near voltage peaks and supplies current to the
load between peaks
C. The capacitor eliminates all load current
D. The capacitor converts DC into a pure sine wave
A smoothing capacitor charges when the rectified voltage rises above its
stored voltage and discharges into the load as the source voltage falls. This
reduces the magnitude of output voltage ripple.
