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EM1 > Motor Controllers > Flashcards

Motor Controllers Flashcards

1
Q

What are the two general methods of starting motors electromagnetically

A

Manually and automatically

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2
Q

By what means are the contractors of a magnetic controller operated

A

Electromechanical devices
Remote control master switch
By a locally controlled master switch

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3
Q

What type of controller is used to start a 1/4hp-dc motor

A

A dc across the line motor controller

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4
Q

What type of controller is used to insert resistance in the secondary circuit of a wound rotor motor

A

An ac secondary resistor

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5
Q

What is the major advantage of the closed transition transformer I’ve r the open transition transformer

A

The motor can’t slip out of phase during the transition phase

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6
Q

Which of the following is a disadvantage of an open transition compensator

A

The motor may slip out of phase during transition, causing an overload

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7
Q

By what means is the designation of a magnetic controller shown?

A

Numerically, according to the max horsepower rating of the connected load

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8
Q

What type of controller enclosure provides the least amount of ventilation to the internal components

A

Submersible

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9
Q

If a master switch is mounted in the controller it is classified as what type of switch

A

Local

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10
Q

What is the purpose of arcing contacts

A

To reduce the amount of arcing at the main contacts when opening or closing

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11
Q

What method of any should you use to keep arcing contacts clean

A

None; they are self cleaning

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12
Q

By what means do magnetic blowout coils quench the arc across contacts

A

By providing a magnetic flux that blows out the arc

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13
Q

When the energized contacts in an ac contractor are opened, what method is used to quench the arc that is created

A

An air gal dissipates the arc

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14
Q

What factor allows ac contractor coils to be smaller than dc coils rated for the same voltage

A

Inductive reactance causes counter emf to limit current flow in an ac coil

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15
Q

A controller protecting a motor is able to disconnect it from the power supply, keep it disconnected, and then restart it automatically when conditions return to normal. Which of the following forms of protection is the controller providing

A

Low-voltage release

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16
Q

Shunt contractors will handle ul to what (a) current at what (b) voltage

A

600A

230V

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17
Q

What material is used to construct the arcing contacts of a dc controller

A

Copper with a heavy coating of cadmium

18
Q

What is the major difference between an LVR and an LVRE controller

A

The LVRE does not use a coil in its circuit to operate the contacts

19
Q

You are installing a new 450-volt, three phase motor controller according to a ship alteration. If the motor is rated at 15hp, you should use what size controller?

A

2

20
Q

What means is used to determine the speed of ac squirrel cage induction motors?

A

The speed of the rotating magnetic field

21
Q

What means should you use to change the speed of an ac motor through the controller?

A

Chang edge connections to the motor

22
Q

One type of a motor speed controller controls the speed of the ac motor by performing which of the following actions?

A

Switching from one set of stator windings to another

23
Q

What means is used to determine the speed of dc motors

A

The amount of current flowing through

24
Q

A reversing type of controller protects a three phase induction motor again ash low voltage and overload by causing the motor to stop running due to line voltage failure. After line voltage is restored, what action, if any, should you perform to restart the motor?

A

Press the forward or reverse bush buttons

25
Q

What is the most common method used to reverse the direction of rotation of a dc motor through a controller?

A

Reversing the connection of the armature with respect to the field

26
Q

Three phase auto transformers are used to start three-phase induction motors and synchronous motors because they have the ability to perform what function?

A

Furnish variable voltage

27
Q

By tapping an auto transformer, it is possible to obtain a voltage higher than the source voltage

A

False

28
Q

What is the most common application of logic controllers aboard ship?

A

Elevator control

29
Q

Logic devices and controller have what advantage over standard electrical components?

A

They have a quicker response.
They don’t have any moving parts
They consume less power

30
Q

In a magnetic circuit breaker, what circuit is opened by an overlay relay

A

The operating coil of the main contractor

31
Q

What is a coarse adjustment to the thermal overload relay?

A

Changing the heater element

32
Q

The tripling current of magnetic overload relays must be set higher than the starting current of the motor they serve

A

True

33
Q

What is not considered a thermal overload relay

A

Dashpot

34
Q

A heat sensitive element that lengthens when heated to open the contacts is used in what type of thermal overload relay

A

Single metal

35
Q

What type of thermal overload relay is manufactures for exclusive use in ac circuits

A

Induction

36
Q

In relation to the starting current of the motor they serve, the tripling current of the magnetic overload relay must be set in what way

A

Higher then the starting current

37
Q

In the instantaneous and time-delay magnetic overload relays, you should use what method to adjust the current settings?

A

Change the distance between the induction coil and the tube

38
Q

Which of the following types of overload relays require a time delay before it is reset

A

Solder pot

39
Q

Symptom:
Over head contact tips

A

Insufficient tip pressure

40
Q

Symptom:
Short contact life

A

Excessive jogging

41
Q

Symptom:
Coil failure (not overheated)

A

Mechanically damaged

EM1 (12 decks)

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