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Exam prep > ILT166 > Flashcards

ILT166 Flashcards

1
Q

What is the purpose of a commutator on a DC motor?

A

To maintain the proper direction of current flow to the armature conductors

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2
Q

What three things does an electric motor require?

A

External source voltage, a magnetic field, and a conductor

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3
Q

What is torque?

A

The turning force produced by a rotor

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4
Q

What are the two basic categories of electric motors?

A

AC and DC

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5
Q

An electric motor uses _____ and _____ to operate

A

Electric current, Magnetism

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6
Q

On a 3 phase AC motor, the stator windings are arranged to create _____

A

a rotating magnetic field

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7
Q

DC compound motors are used to operate loads that require _____

A

Low starting torque

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8
Q

A DC shunt motor should never be operated with _____

A

The field circuit open

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9
Q

What will happen if the field current of a shunt-type DC motor is held constant and the armature voltage is increased?

A

The speed of the motor will increase

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10
Q

The direction of rotation of a shunt wound DC motor is change by reversing the _____, not the _____

A

Current flow, Field

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11
Q

A shunt type DC motor is known to have a _____

A

High starting torque

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12
Q

The direction of rotation in a 3-phase induction motor is determined by the _____

A

Phase sequence

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13
Q

What happens when a load is applied to a 3-phase squirrel cage induction motor?

A

The rotor speed will decrease slightly

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14
Q

What is the synchronous speed of an induction motor?

A

The speed of the rotating magnetic field

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15
Q

When dual-voltage, 9 lead wye-connected, 3-phase motor is connected for high voltage are the coils connected in series or parallel?

A

Series

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16
Q

As the load on an induction motor increases the power factor will _____

A

Decrease

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17
Q

How can the speed of a squirrel cage motor be varied?

A

By varying the supplied frequency

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18
Q

A variable A/C motor drive delivers _____ and _____

A

Fixed line voltage, variable frequency

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19
Q

A permanent capacity motor does not require a _____

A

Centrifugal switch

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20
Q

Which motor has the highest starting torque of all the single phase motors?

A

A capacitor start/ capacitor run motor

21
Q

A wound rotor induction motor is normally started with _____

A

DC voltage applied to the rotor

22
Q

Current flow through the windings of a transformer can generate _____

A

Heat loss

23
Q

What is impedance matching?

A

adjusting the impedance to produce the desired energy transfer

24
Q

What happens to current in a step-up transformer?

A

It is stepped down

25
Q

What is the turns ratio?

A

The ratio of the number of turns in the secondary winding to the number of turns in the primary winding

26
Q

When a transformer is connected to a pure inductive-resistive-capacitive load, the circuit is purely _____

A

resistive at resonance

27
Q

When is a transformer likely to overheat?

A

When the transformer is operating above its secondary voltage

28
Q

What must be known to calculate the power rating of a transformer?

A

Voltage and current ratings

29
Q

How can you reduce the cost of power lines?

A

Reducing current and increasing voltage

30
Q

What are the two sets of windings in most transformers?

A

Primary and secondary

31
Q

Why are induced currents bad in an iron core?

A

They produce heat and use power

32
Q

Transformer efficiency is the ratio of _____ to _____

A

output current to input current

33
Q

What determines a transformer’s classification?

A

Its operating frequency

34
Q

What is one advantage of an autotransformer?

A

Current flow through the windings is reduced

35
Q

What do buck and boost transformers do?

A

Either raise or lower line voltage

36
Q

In an AC transformer, currents lag their respective voltages by _____ degrees

A

90

37
Q

What is an isolation transformer used for?

A

Electrically separating the source voltage and the load

38
Q

What is a transformer?

A

An electrical device that uses magnetism to change voltage from one level to another or isolate one voltage from another

39
Q

What is flux loss?

A

Power loss in a transformer caused by resistance of the copper windings

40
Q

What is eddy current loss?

A

Power loss due to currents induced in the metal structure from the magnetic field

41
Q

What is the standard frequency for power distribution in North America?

A

60 Hz

42
Q

What is a core type transformer?

A

A transformer with windings placed around each leg of the core

43
Q

What letter represents the secondary winding leads?

A

X

44
Q

What unit are AC transformers rated with?

A

kVA

45
Q

What is an autotransformer used for?

A

To raise and lower voltage as required by the circuit

46
Q

Do current ratings specify the primary or secondary windings?

A

Secondary

47
Q

What is the turns ratio?

A

The number of flux lines linking the primary and secondary transformer windings

48
Q

If a transformer has a turns ratio of 2:1 will it step down or step up the voltage?

A

Step down

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