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What Naval Ship's Technical Manual (NSTM) deals with electric motors and motor controllers?
NSTM302.
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How does a magnetic motor controller function?
The contacts are opened by electromechanical devices.
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What is the most common type of motor controller found on Gas Turbine vessels? Magnetic across-the-line type.
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What is a master switch?
A device that controls the electric operation of a motor controller.
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Float, limit, and pressure switches are all examples of what type of master switches?
Automatic master switches.
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Multi contact switches are classified in what manner? By the number of poles and the number of
throws.
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Accurate snap-acting type switches are commonly known by what name? Microswitches.
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What are 8 types of microswitches?
Lever, leaf, pin-plunger, roller lever, roller leaf, overtravel plunger, panel-mount plunger, panel-mount roller plunger.
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A microswitch with a leaf roller is used for what application?
Low-force, slow moving cams or slides.
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What are two basic methods used to check a switch?
An ohmmeter or a voltmeter.
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The speed of a two-speed AC induction motor is controlled by what?
By shifting from one set of windings to another.
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What does the acronym LVP stand for?
Low voltage protection.
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What type of controller uses a closed-transition compensator which keeps the motor connected to the supply line during the entire transition period?
Autotransformer controller.
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What happens to electrical equipment with LVP installed upon a loss of supply power? You must manually restart the controller.
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How does a LVR controller function?
When supply voltage is reduced or lost altogether the controller disconnects the motor from the supply, when power is returned it restarts.
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Most small manual across-the-line controllers are equipped with what type of voltage protection?
LVRE - Low voltage release effect.
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Nearly all shipboard motor controllers are protected from excessive current by?
Overload relays
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What are the two types of overload relays installed on shipboard controllers?
Thermal and Magnetic.
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What are the four types of thermal overload relays?
Solder-pot, Bimetal, Single-metal, and Induction.
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What type of thermal overload relay uses a heat-sensitive element connecting a cylinder to a hollow tube?
Solder-pot type.
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When adjusting a thermal overload relay a coarse adjustment is achieved by?
Changing the heater element.
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How does a Bimetal type overload relay function?
When heated the strip or coil deflects because one metal expands more than the other. The deflection causes the overload relay to open.
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What type of thermal overload relay can be used for AC or DC?
Induction type.
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An overload relay that has a coil connected in series with the motor circuit and a tripping armature or plunger is known as?
A Magnetic overload relay.
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Controllers are protected from short circuits by?
A circuit breaker in the power supply system.
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How is short circuit protection provided for in control circuits?
By fuses in the controller enclosure.
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After a thermal overload relay has tripped, the relay must be allowed to cool for what duration of time before resetting the relay?
1 minute or longer.
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What are three types of overload relay resets?
Manual, automatic, and electrical.
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A chattering controller usually is attributed to what?
Dirty relay contacts.
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What provides uninterruptable power to the 60 Hz ship's service power system upon a loss of power?
Battery backup systems.
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What system is known as the uninterruptable power system?
The UPS system.
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Propulsion electronics operate at what power range?
115/120 Volt range.
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The batteries in the UPS system generate what type of power?
Low-voltage DC power.
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What type of batteries are used in the UPS system?
Acid-lead Wet cell type.
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What type of controller uses an electromechanical device to open and close contacts?
A magnetic controller.
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A resistor controller is only used for what type of applications?
DC only.
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What type of controller starts the motor at reduced voltage through an auto-transformer?
A compensator controller.
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Name two types of compensator controllers?
Open transition and closed transition.
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How are controllers classified?
As either manual or magnetic.
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What is the most common type of AC controller?
Across-line type.
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What device protects the motor from overheating by excessive current?
An overload relay.
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Overload relays are classified into what two types?
Magnetic and thermal.
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What type of overload relay has a coil connected in series with the motor load circuit and a tripping armature or plunger?
Magnetic type
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Name two types of magnetic overload relays?
Instantaneous and time-delay type.
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What is the most common type of time-delay magnetic overload relay?
An oil dashpot with a piston attached to the tripping armature.
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What determines the speed of operation on a time-delay magnetic overload relay? he size of the hole in the piston.
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How is the tripping current adjusted in both the instantaneous and time-delay magnetic overload relays?
By changing the distance between the series coil and the tripping armature.
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What effect does ambient temperature have on magnetic overload relay operation?
None.
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What are four types of thermal overload relays?
Solder pot, bimetal, single metal and induction.
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What thermal overload is constructed of a cylinder inside a hollow tube held together by solder?
Solder pot type.
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What type of thermal overload can only be used for AC applications?
Induction type.
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The copper tube within an induction type thermal overload relay serves what function?
Acts as the short circuited secondary of a transformer and is heated by the current induced in it.
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The heat-sensitive element within the induction type overload relay is of what design?
Bimetal strip or coil.
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How is a rough adjustment made on a thermal overload relay?
By changing the heater element.
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What are three methods of resetting a tripped overload relay?
Manual (hand), automatic and electric reset.
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What is the most common type of reset method used on overload relays?
Manual or hand reset.
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Where is the hand reset normally located?
In the controller enclosure.
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What type of overload relay reset device is reset by spring tension or gravity?
Automatic reset device.
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When is full field protection required?
It is required in controllers for DC motors in which a shunt field rheostat or resistor is used to weaken the motor field and obtain motor operation at speeds in excess of 150 percent of the rated field current.
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What is a solenoid?
A control device that uses electromagnetism to convert electrical energy into mechanical motion.
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What is the inner core of the solenoid constructed of?
Soft-iron.
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What energizes the solenoid?
A switch or relay.
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The solenoid's effective strength within the magnetic field and the plunger will vary based on what variable?
The distance between the plunger and the core.
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What links the solenoid to the relay?
Electrical wiring.
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What is the difference between a solenoid and a relay?
The relay does not have a movable core (plunger).
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Power relays are commonly called what?
Contactors.
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What does the term "cone and crater" mean when associated with a relay?
A detrimental effect caused by current flowing in one direction through the relay.
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What is the advantage of a relay equipped with ball-shaped contacts?
Dust or other substances are not as readily deposited on a ball-shaped surface.
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Which type of relay is used to control low power common circuits?
Control relay.
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Anchor windlasses use what form of circuit protection to prevent excessive motor overloading?
Jamming or step-back protection.
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Electrical brakes are normally operated with what type of driver?
solenoid or motor.
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What type of tool is used to clean ball-shaped contacts?
burnishing tool.
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After using a burnishing tool it should be immediately cleaned with what?
Alcohol.
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What special tool is used to straighten bent contacts in a relay?
point bender.
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