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Flashcards in ILT166 Deck (48):
1

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

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

2

What three things does an electric motor require?

External source voltage, a magnetic field, and a conductor

3

What is torque?

The turning force produced by a rotor

4

What are the two basic categories of electric motors?

AC and DC

5

An electric motor uses _____ and _____ to operate

Electric current, Magnetism

6

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

a rotating magnetic field

7

DC compound motors are used to operate loads that require _____

Low starting torque

8

A DC shunt motor should never be operated with _____

The field circuit open

9

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

The speed of the motor will increase

10

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

Current flow, Field

11

A shunt type DC motor is known to have a _____

High starting torque

12

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

Phase sequence

13

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

The rotor speed will decrease slightly

14

What is the synchronous speed of an induction motor?

The speed of the rotating magnetic field

15

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

Series

16

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

Decrease

17

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

By varying the supplied frequency

18

A variable A/C motor drive delivers _____ and _____

Fixed line voltage, variable frequency

19

A permanent capacity motor does not require a _____

Centrifugal switch

20

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

A capacitor start/ capacitor run motor

21

A wound rotor induction motor is normally started with _____

DC voltage applied to the rotor

22

Current flow through the windings of a transformer can generate _____

Heat loss

23

What is impedance matching?

adjusting the impedance to produce the desired energy transfer

24

What happens to current in a step-up transformer?

It is stepped down

25

What is the turns ratio?

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

26

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

resistive at resonance

27

When is a transformer likely to overheat?

When the transformer is operating above its secondary voltage

28

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

Voltage and current ratings

29

How can you reduce the cost of power lines?

Reducing current and increasing voltage

30

What are the two sets of windings in most transformers?

Primary and secondary

31

Why are induced currents bad in an iron core?

They produce heat and use power

32

Transformer efficiency is the ratio of _____ to _____

output current to input current

33

What determines a transformer's classification?

Its operating frequency

34

What is one advantage of an autotransformer?

Current flow through the windings is reduced

35

What do buck and boost transformers do?

Either raise or lower line voltage

36

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

90

37

What is an isolation transformer used for?

Electrically separating the source voltage and the load

38

What is a transformer?

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

39

What is flux loss?

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

40

What is eddy current loss?

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

41

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

60 Hz

42

What is a core type transformer?

A transformer with windings placed around each leg of the core

43

What letter represents the secondary winding leads?

X

44

What unit are AC transformers rated with?

kVA

45

What is an autotransformer used for?

To raise and lower voltage as required by the circuit

46

Do current ratings specify the primary or secondary windings?

Secondary

47

What is the turns ratio?

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

48

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

Step down