ILT166

Question 1

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

Answer 1

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

Question 2

What three things does an electric motor require?

Answer 2

External source voltage, a magnetic field, and a conductor

Question 3

What is torque?

Answer 3

The turning force produced by a rotor

Question 4

What are the two basic categories of electric motors?

Answer 4

AC and DC

Question 5

An electric motor uses _____ and _____ to operate

Answer 5

Electric current, Magnetism

Question 6

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

Answer 6

a rotating magnetic field

Question 7

DC compound motors are used to operate loads that require _____

Answer 7

Low starting torque

Question 8

A DC shunt motor should never be operated with _____

Answer 8

The field circuit open

Question 9

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

Answer 9

The speed of the motor will increase

Question 10

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

Answer 10

Current flow, Field

Question 11

A shunt type DC motor is known to have a _____

Answer 11

High starting torque

Question 12

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

Answer 12

Phase sequence

Question 13

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

Answer 13

The rotor speed will decrease slightly

Question 14

What is the synchronous speed of an induction motor?

Answer 14

The speed of the rotating magnetic field

Question 15

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

Answer 15

Series

Question 16

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

Answer 16

Decrease

Question 17

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

Answer 17

By varying the supplied frequency

Question 18

A variable A/C motor drive delivers _____ and _____

Answer 18

Fixed line voltage, variable frequency

Question 19

A permanent capacity motor does not require a _____

Answer 19

Centrifugal switch

Question 20

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

Answer 20

A capacitor start/ capacitor run motor

Question 21

A wound rotor induction motor is normally started with _____

Answer 21

DC voltage applied to the rotor

Question 22

Current flow through the windings of a transformer can generate _____

Answer 22

Heat loss

Question 23

What is impedance matching?

Answer 23

adjusting the impedance to produce the desired energy transfer

Question 24

What happens to current in a step-up transformer?

Answer 24

It is stepped down

Question 25

What is the turns ratio?

Answer 25

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

Question 26

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

Answer 26

resistive at resonance

Question 27

When is a transformer likely to overheat?

Answer 27

When the transformer is operating above its secondary voltage

Question 28

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

Answer 28

Voltage and current ratings

Question 29

How can you reduce the cost of power lines?

Answer 29

Reducing current and increasing voltage

Question 30

What are the two sets of windings in most transformers?

Answer 30

Primary and secondary

Question 31

Why are induced currents bad in an iron core?

Answer 31

They produce heat and use power

Question 32

Transformer efficiency is the ratio of _____ to _____

Answer 32

output current to input current

Question 33

What determines a transformer's classification?

Answer 33

Its operating frequency

Question 34

What is one advantage of an autotransformer?

Answer 34

Current flow through the windings is reduced

Question 35

What do buck and boost transformers do?

Answer 35

Either raise or lower line voltage

Question 36

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

Answer 36

90

Question 37

What is an isolation transformer used for?

Answer 37

Electrically separating the source voltage and the load

Question 38

What is a transformer?

Answer 38

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

Question 39

What is flux loss?

Answer 39

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

Question 40

What is eddy current loss?

Answer 40

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

Question 41

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

Answer 41

60 Hz

Question 42

What is a core type transformer?

Answer 42

A transformer with windings placed around each leg of the core

Question 43

What letter represents the secondary winding leads?

Answer 43

X

Question 44

What unit are AC transformers rated with?

Answer 44

kVA

Question 45

What is an autotransformer used for?

Answer 45

To raise and lower voltage as required by the circuit

Question 46

Do current ratings specify the primary or secondary windings?

Answer 46

Secondary

Question 47

What is the turns ratio?

Answer 47

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

Question 48

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

Answer 48

Step down