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WorksheetsElectricidad 1
Total questions: 50
Worksheet time: 25mins
When troubleshooting a console circuit card suspected of being faulty, first check for proper voltages to the card and then __________.
test transistors or integrated circuits for gain and compare with manufacturer's specifications
blow any accumulated dust from the card with at least 30 psi air from the ship's service air system
pull the card, clean the sliding connections with a pencil eraser, and remove accumulated dust
de-energize the card and check the printed circuit traces for continuity with an ohmmeter
In the illustrated circuit the voltage is provided by a 12 Volt lead acid battery and the resistor value is 3 ohms. If the battery is rated for 120 amp-hours, how long will it take before the voltage will drop to 1.75 volts per cell?
12 hours
1.75 days
30 hours
2.5 days
Electrostatic forces in high voltage circuits cause indicating instruments to give __________.
parallax readings
highly intuitive readings
highly accurate readings
inaccurate readings
When paralleling two AC generators, the frequency of the machine coming on-line, immediately prior to closing its breaker, should be __________.
slightly less than the oncoming generator frequency
the same as the bus frequency
slightly greater than the bus frequency
the same as the bus voltage
The greatest single cause of electrical failures is __________.
the breakdown of insulation
overcurrent
high inductance
too frequent testing
As shown in the illustration if the applied voltage is 12 VDC, the resistance of R1 is 10 ohms, and R2 is 10 ohms what is the total power consumed by the circuit?
3.6 watts
72 watts
7.2 watts
36 watts
Which of the conditions listed will indicate the need to clean the insulation on the windings of an electric motor?
Higher than normal operating temperature.
Excessive vibration at normal speed.
Sparking at the brushes.
High megger readings.
Thermal strip heaters are provided in DC main propulsion motors to __________.
prevent moisture buildup in windings
maintain a relatively constant temperature in the motor enclosure
prevent the rotor from warping
provide an additional means of starting resistance
A carbon resistor has the following color bands; Band A is yellow, followed by violet, gold, and silver. What is the ohmic value of the resistor?
4.7 ohms + or - 10%
47 ohms + or - 5%
4700 ohms + or - 10%
4.7 K ohms + or - 5%
Electrical failures in motors are caused by the breakdown of insulation, which may be caused by __________.
penetration of moisture
accumulation of dirt
overheating
all of the above
The energy consumed by an AC motor, as strictly reactive power, is __________.
used to do mechanical work
used to establish the magnetic field of the motor
lost as heat generated by bearing friction
lost in doing work to turn the motor itself
Sparking at the brushes of a DC propulsion motor can be the result of __________.
improper brush pressure
improper brush seating
reversed interpole polarity
all of the above
When a voltage of 124 VDC is applied to the illustrated circuit with a resistance of 32 ohms the current will be __________.
0.258 amps
3.875 amps
8.258 amps
156 amps
A three-phase electrical system is equipped with ground detecting lamps. If one of the lamps is dark, and remains dark when the test switch is operated, this indicates __________.
the dark lamp must be replaced
there is a ground in the line with the dark lamp
there are grounds in two of the three phases
the voltage to the dark lamp is less than that of the system
In process control terminology, continuously variable values which change without distinct increments, such as temperature, pressure, or level are called __________.
binary values
digital values
bumpless values
analog values
Copper is often used as an electrical conductor because it __________.
has high resistance at low temperatures
has a highly polished surface
is able to pass current with little opposition
holds insulation together well
A capacitor can be tested using a megohmmeter or an ohmmeter. If the meter is connected to a shorted capacitor, the meter pointer should __________.
immediately swing to the maximum resistance value for the capacitor
first swing quickly to 'zero', then gradually move up the scale as the capacitor charges
immediately deflect to and remain at zero
immediately swing to a high reading and then gradually decrease
Which section of the circuit shown in the illustration changes AC to DC?
I
II
III
IV
A shunt-wound DC generator is one in which the shunt field windings are in parallel with the __________.
commutator
brushes
armature
all of the above
Although saturable reactors are extremely useful in some applications, their gain is low because of __________.
core hysteresis losses
inductive reactance in the control winding
IR drop throughout the load winding
all of the above
Reversing any two of the three rotor leads on a wound-rotor induction motor will __________.
increase motor performance
decrease motor performance
reverse the motor rotation
have no effect on the direction of rotation or motor performance
The counter EMF produced in the windings of a DC motor is 'zero' when the __________.
armature has just begun to turn
armature is not turning
motor is almost up to rated speed
motor is at rated speed
When the operating handle of a molded-case circuit breaker is in the mid-position, this indicates that the circuit breaker is __________.
on
off
reset
tripped
Which of the following materials is a good electrical insulator?
wood
silver
copper
gold
If the pointer on a megger fails to return to 'zero' when not being used, the __________.
megger is out of calibration
megger is operating normally
hairsprings are burned out
pointer probably stuck in that position
When a megohmmeter is being used to test insulation resistance, current leakage along the surface of the insulation is indicated by the megohmmeter pointer __________.
fluctuating around a constant resistance reading
dipping towards 'zero', then rising slowly
kicking slightly downscale as voltage is applied
continually rising as the test voltage is applied
Before servicing the device indicated as "A" in panels #1 and #3 of the illustration, the device labeled 'CT' must __________.
have the disconnected leads taped to prevent short circuiting.
only be connected to multimeter on the ammeter setting
be short circuited
have one lead grounded to discharge static electricity for the prevention of damage to electronic components
Which of the following statements is true concerning a step-down transformer in an operating AC power circuit?
Voltage and current will both be increased.
Voltage and current will both be decreased
Voltage decreases as current increases.
Voltage increases as current decreases.
When working on electrical circuits containing large capacitors, in addition to de-energizing the circuit, which of the listed precautions should also be taken?
Keep all radio equipment away.
Measure capacitor insulation resistance.
Ground the capacitor terminals.
Check capacitor circuit polarity.
A single-phase induction motor fails to start. The rotor is spun rapidly with the line switch closed. Having started by this method it is noted that the motor fluctuates between a very slow speed and half speed. The problem probably lies in the ______
starting winding
centrifugal mechanism
centrifugal switch
running winding
A carbon resistor has the following color bands; Band A is yellow, followed by violet, yellow, and silver. What is the value of the resistor in ohms?
74 ohms + or - 5%
4700 ohms + or - 10%
74,000 ohms + or - 5%
470,000 ohms + or - 10%
The prime mover of an AC two pole main propulsion generator drives the generator at 3600 RPM. If the main propulsion motor has 80 poles, what will be the propeller speed?
45 RPM
80 RPM
90 RPM
180 RPM
When power is restored after a complete power failure, the steering gear pump motor which was on-line, will normally __________.
have to be restarted
have to be reset
restart automatically
trip its overload relays
Accidental grounds in a shipboard electrical system must be repaired as soon as possible as they will __________.
result in immediate power outages
damage circuit breakers
appear on the ground detection system
damage insulation and may cause outages
Three 12 volt, lead-acid, batteries connected in series will develop __________.
12 volts
24 volts
36 volts
48 volts
When a lead-acid battery starts to gas freely after receiving a normal charge current, the charging current should be __________.
slightly increased
shut off
decreased to a trickle charge current
maintained for an additional hour
When a voltage of 442.7 VDC is applied to the illustrated circuit with a resistance of 1.25 ohms the current will be __________.
28.25 amps
35.32 amps
354.16 amps
443.62 amps
For routine cleaning of a commutator, you should apply __________.
course sandpaper in a slow back and forth motion across the commutator slots
an emery cloth parallel to the axis of the commutator
a canvas wiper on the commutator while running
a fine tooth file to the commutator while running
The load sharing characteristics of two diesel alternators operating in parallel are directly related to the setting of their governors' __________.
load limit
idle speed
speed limit
speed droop
The reversal of an AC, three-phase, induction motor is accomplished by __________.
changing all three motor leads
reversing the position of the slip rings
interchanging any two of the three motor leads
interchanging any two brushes
In D.C. motor construction, the armature coils' ends are __________.
soldered to the commutator bar risers
imbedded into core slots
crimped together with brush pigtails
spliced with the field windings
In the illustration, the component labeled 'EXC' is __________.
a separate class II regulated DC generator for critical direct current loads
a generator feeding the FLD winding through the voltage regulator.
the controller to drive the governor for turbo generator speed.
the electronic driver for the switchboard metering circuits
Which of the listed conditions could indicate the need for cleaning electrical insulation?
Low ambient temperature
Low operating temperature
High dielectric strength
Low megger readings
A current-carrying conductor makes accidental contact with a wiring conduit. This will be indicated by a __________.
low switchboard wattmeter reading
high switchboard wattmeter reading
darkened switchboard ground detecting lamp
darkened switchboard synchronizing lamps
The power supplied to a motor is six kilowatts at 120 volts. What is the impedance of the motor?
0.05 Ohms
0.50 Ohms
2.40 Ohms
24.00 Ohms
Which of the following statements concerning nickel-cadmium batteries is true?
Nickel-cadmium batteries are less susceptible to local action than lead-acid batteries.
Nickel-cadmium batteries should only be discharged 50% before recharging.
The electrolyte of an idle nickel-cadmium battery must be replaced monthly to maintain battery condition.
When mixing electrolyte always add acid to the water.
If the synchronous speed of a 12 pole, polyphase, induction motor operating at 60 Hz were 600 RPM, how many poles will be required in a similar motor operating at the same frequency but having a synchronous speed of 900 RPM?
4
6
8
18
The plates of a wet cell NiCad storage battery are made from __________.
potassium hydroxide and nickel sulfate
cadmium sulfate and lead peroxide
silver oxide and cadmium sulfate
nickel hydroxide and cadmium hydroxide
Cartridge type fuses contain meltable elements that are generally made from __________.
mild steel
aluminum alloy
copper alloy
lead alloy
When a voltage of 110 VDC is applied to the illustrated circuit with a resistance of 237 ohms the current will be __________.
.464 amps
1.464 amps
2.154 amps
3.47 amps
