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WorksheetsElectricidad 9
Total questions: 50
Worksheet time: 25mins
A diesel driven emergency generator is prevented from being paralleled with the ship's service generators by __________.
an electrical interlock system
an automatic paralleling trip switch
the synchronizing oscilloscope
the reverse current relay
As load is added to a DC shunt motor, the motor will __________.
speed up
maintain the same speed
slow down slightly
stop
The purpose of having low voltage protection for an electric motor circuit is to __________.
prevent severe arcing or sparking
protect against reversal of power in the main circuit
prevent excessive current from developing as it is attempting to deliver its required horsepower
prevent the motor from overspeeding
Proper maintenance of a D.C. motor's commutator includes __________.
side-cutting the copper segments and undercutting the mica
coating the copper surface with light machine oil for the first four hours of operation
baking the armature in an oven at 350°C for 8 hours annually
all of the above
Which of the following is a characteristic of fractional horsepower repulsion start motors?
They start with a rotating stator field.
The short circuiting ring is removed from the commutator while starting.
The brushes are removed from the commutator while starting.
They have a low starting torque.
When troubleshooting a lead-acid storage battery, a weak or dead cell is best detected by __________.
comparing the specific gravity of the electrolyte in each cell
taking an open circuit voltage test of individual cells
visually inspecting the electrolyte levels of each cell
taking each cell's temperature with a calibrated mercury thermometer
What is the approximate discharge voltage produced by one wet cell of a nickel-cadmium battery?
1.25 volts
1.5 volts
2.2 volts
6.0 volts
Which of the devices listed is indicated by the electronic symbol lettered as "A", shown in the illustration?
Thyristor
Diode
Capacitor
Transistor
Electrical power loss due to hysteresis is a result of __________.
arcing at the brushes
pulsating terminal current
heat generated by magnetic polarity reversals
excessive field current
If a small electric motor is immersed in salt water it should be __________.
I. washed in fresh water and thoroughly dried
II. initially started with reduced voltage
I only
II only
both I and II
neither I or II
Wet armature windings in a D.C. motor may lead to __________.
reduced voltage
reduced current
increased resistance
overheating
A low voltage source is applied to the collector rings of a salient-pole alternator to test for shorted coils. As the voltage drop across each coil is recorded, a coil with a short circuit will be indicated by a __________.
high voltage reading, while the other coil readings will have an equal or lower value
low or zero voltage reading, while the other coils will have higher readings
fluctuating voltmeter reading, while the other coil readings are steady
steady voltmeter reading, while the other coil readings are fluctuating
AC and DC generators are similar in that they __________.
both initially generate alternating voltages
both rectify the voltage before delivery
both operate at 60 cycles
both supply three-phase power
AC generator circuits are protected against malfunctions due to prime mover power loss by the use of __________.
main bus disconnect links
a separate battery backup
reverse current relays
reverse power relays
A megger is being used to test the insulation of an AC generator. The resistance value of a dry, clean winding will __________.
continue to rise as test potential is maintained, becoming fairly steady as the dielectric-absorption effect of insulation stabilizes
remain constant as the temperature of the windings increases
continue to drop as test potential is maintained, becoming fairly steady after 5-7 minutes
stabilize after approximately 2-4 minutes of fluctuation
Which of the following represents the accepted method of cleaning dust and foreign particles from electrical equipment while limiting damage to electric components?
Carefully using a soft copper bristle brush.
Blowing a high velocity stream of compressed air rapidly across the components.
Using a vacuum cleaner to remove debris from the components.
Using carbon tetrachloride as a cleaning solvent to clean the components.
Materials that retain a large part of their magnetization, after the magnetizing force is removed, are said to have __________.
low hysteresis loss
high flux density
high permanence
high ductility
The air gap provided in an induction motor should be checked periodically with a feeler gage to detect __________.
any decrease in motor magnetizing current
an increase in hysteresis loss
increase in apparent power factor
any increase in rotor bearing wear
To best determine the state of charge of a wet cell nickel-cadmium battery, you should __________.
measure the output amperage
measure the voltage while under a load
test the electrolyte specific gravity
use a ohm meter on the highest scale
Brushes in a generator must be positioned in the neutral plane to avoid sparking between the brushes and the __________.
yoke
armature windings
field pole windings
commutator
When a nickel-cadmium battery begins gassing while connected to the battery charging circuit, you should __________.
do nothing as this is a normal condition when charging
add distilled water to each cell to increase the specific gravity of the electrolyte
add potassium hydroxide to each cell to reduce the specific gravity of the electrolyte
increase the charging rate
What would be the terminal voltage and amp-hour capacity at terminals A and B if each battery was rated at 50 amp-hours and 12 volts?
12 volts and 50 amp-hours
12 volts and 150 amp-hours
24 volts and 50 amp-hours
24 volts and 150 amp-hours
An advantage of DC motors over AC motors is that they __________.
are less expensive
require less maintenance
offer infinite speed variation
all of the above
Power conversion for use in AC propulsion drive motors can be accomplished by __________.
cyclo-converters
pulse width modulated inverters
load commutated inverters
All of the above
A cyclo-converter (CCV) is a static power converter that __________.
provides adjustable frequency to power an ac propulsion drive motor
converts ac power to dc power in a dc propulsion drive system
converts dc power to ac power in an ac propulsion motor
provides constant frequency output power to an ac propulsion drive motor
Which of the listed conditions is an advantage of a PN diode over a vacuum diode?
Smaller size.
No warm up time.
More reliable.
All of the above.
The propulsion motor most often utilized in an ac drive system operating in the moderate to high power range is the ________.
squirrel cage induction type
synchronous type with wound field
wound rotor induction type
split phase induction type
Which of the following statement is FALSE concerning Azipod propulsion systems?
The pod assembly swivels on a vertical axis.
The system allows full turns at high speed.
The system eliminates the need for a separate rudder.
The system requires the use of a controllable pitch propeller.
As shown in the illustration, the electrical symbol is used to indicate which of the listed types of motors?
Shunt motor.
Series motor.
Compound motor.
Tri-field motor.
To determine the state of charge of a wet cell nickel-cadmium battery, you should __________.
check the electrolyte with a hydrometer
use the constant specific gravity method
check no load voltage
check voltage under nominal load
When replacing a fuse with one of a higher rating than the original, which of the following is true?
It endangers the apparatus it is supposed to protect.
It reduces the possibility of short circuits.
It increases the efficiency of the equipment by allowing more current to be used.
It creates a larger voltage drop in the circuit being protected.
Which of the listed electrical devices is represented by the symbol shown in the illustration?
Fixed resistance resistor
Coil with magnetic core
DC motor or generator shunt field
Transformer
The timer element of a reverse power relay will activate when __________.
the power flow is the same as the tripping direction
the power flow is the opposite to the tripping direction
the movement of the disk is damped by a permanent magnet
the load difference between generators is more than 10 percent.
An AC generator power panel is fitted with two synchronizing lamps and a synchroscope. When paralleling, if the synchroscope pointer is at the noon position and one synchronizing light is bright while the other remains dark, this indicates that __________.
the incoming generator voltage is too low
the generators are out of phase and one lamp is burned out
the generators are in phase but one lamp is burned out
the generator breaker may be closed
In the illustrated three phase alternator, line voltage is equal to __________.
1.73 times the phase voltage
the phase voltage
the phase voltage divided by 1.73
the line current
Reduced voltage applied to an AC induction motor during the starting period will __________.
result in decreased acceleration time only
lower the starting current and increase accelerating time
cause a greater starting torque
increase the starting current and pump capacity
The force that causes free electrons to flow in a conductor producing electric current is called a/an __________.
resistant force
electromotive force
inductive force
dielectric force
An alternator will fail to produce line voltage as a result of __________.
a closed circuit breaker
oxidized slip rings
improperly staggered brushes
excitation field failure
When correcting specific gravity readings of a lead-acid battery for existing temperature conditions, you should __________.
always fill the battery with acid prior to taking readings
maintain a load on the battery when taking readings
add correction values for battery temperatures above 80°F
subtract correction values for battery temperatures above 80°F
What will be the output frequency of a three-phase, six pole, AC generator operating at 1800 revolutions per minute?
60 hertz
90 hertz
120 hertz
180 hertz
In a compound-wound motor, a portion of the line current flows through the __________.
shunt field coils
series field coils
interpoles
all of the above
The best method used to properly resurface an eccentric commutator on a small DC electric motor is to ________.
turn it down in the ship's lathe
use a fine tooth file
use a hand stone
burnish it with a commutator stone while running
What power is consumed by a heating element using a current of 20 amperes at 120 volts?
20 watts
66.67 watts
720 watts
2400 watts
How many volts are necessary to provide a current of 10 amperes to a motor with an in-line resistance of 11 ohms?
21 volts
110 volts
220 volts
240 volts
When the current flow in a power transmission line is halved, the power loss __________.
is halved
is doubled
is divided by four
remains the same
If the excitation of an alternator operating in parallel is decreased below normal, its __________.
power factor will change in the lagging direction
power factor will change in the leading direction
ampere load will be greatly increased
kilowatt load will be greatly decreased
Which of the following problems will occur if the circuit breaker of the incoming alternator is closed and it is 180° out of phase with the loaded alternator when paralleling?
The rotor of the loaded alternator will hunt.
Severe cross currents will occur which could cause damage.
The rotor of the incoming alternator will stop.
Both alternators will parallel 180° out of phase.
A loss of field excitation to an AC generator while operating in parallel will cause it to __________.
absorb more and more load due to decreased armature reaction
lose its load due to the inherent speed droop built into the governor
smoke and overload due to field flashover as residual field flux changes polarity
lose its load, begin to motorize, trip out on reverse power relay, and possibly overspeed
An alternator switchboard has a synchroscope and synchronizing lamps. If the synchroscope is broken, which of the steps listed is the most essential before an alternator can be paralleled with the bus?
The breaker should be closed when one synchronizing lamp is dark and the other is bright.
The breaker should be closed when both synchronizing lamps are bright.
The frequency meter should be used to determine that the incoming alternator frequency is slightly higher than the bus.
A portable phase sequence indicator must be used to verify the information from the lamps.
The electrical schematic shown in the illustration represents a/an __________.
across-the-line starter
primary-resistor starter
autotransformer starter
part-winding starter
