Theory Units 21-24

Question 1

A motor uses opposing electromagnetic fields in order to rotate the motor shaft. The stationary electromagnetic field is created by the _____, and the rotating electromagnetic field is created by the _____.

Answer 1: stator, rotor
Answer 2: rotor, stator
Answer 3: winding A, winding B
Answer 4: none of these

Answer 1

stator, rotor

Theory 21.2(A)

Question 2

The electromagnetic field on one side of the rotor causes a(an) _____ force and on the other side a(an) _____ force against the stator’s magnetic field.

Answer 1: downward, upward
Answer 2: upward, downward
Answer 3: spinning, static
Answer 4: none of these

Answer 2

downward, upward

Theory 21.2(C)

Question 3

What size motor in horsepower is required to produce approximately 60 kW of output watts?

Answer 1: 50 hp
Answer 2: 60 hp
Answer 3: 70 hp
Answer 4: 80 hp

Answer 3

80 hp

Theory 21.3

Question 4

What size motor in horsepower is required to produce approximately 110 kW of output watts?

Answer 1: 75 hp
Answer 2: 100 hp
Answer 3: 125 hp
Answer 4: 150 hp

Answer 4

150 hp

Theory 21.3

Question 5

What is the approximate output watts of a 5 hp motor?

Answer 1: 3.75 kW
Answer 2: 4.75 kW
Answer 3: 6.75 kW
Answer 4: 7.75 kW

Answer 5

3.75 kW

Theory 21.3

Question 6

What is the approximate output in watts of a 25 hp motor?

Answer 1: 18.65 kW
Answer 2: 19.50 kW
Answer 3: 22.75 kW
Answer 4: 31.45 kW

Answer 6

18.65 kW

Theory 21.3

Question 7

Once a motor begins turning, the rotor windings are increasingly cut by the stationary magnetic field, resulting in an increasing counter-electromotive force in the _____.

Answer 1: stator
Answer 2: rotor
Answer 3: shaft
Answer 4: any of these

Answer 7

rotor

Theory 21.4(B)

Question 8

A motor that operates at _____ will cause its windings to overheat to the point where the wire windings’ insulation and lubrication will be damaged.

Answer 1: FLA
Answer 2: FLC
Answer 3: LRC
Answer 4: any of these

Answer 8

LRC

Theory 21.4(C)(2)

Question 9

What is the nameplate FLA for a 5 hp, 230V, single-phase motor with 93 percent power factor and 87 percent efficiency?

Answer 1: 10A
Answer 2: 20A
Answer 3: 28A
Answer 4: 35A

Answer 9

20A

Theory 21.5(B)

Question 10

What is the nameplate FLA for a 20 hp, 208V, three-phase motor with 90 percent power factor and 80 percent efficiency?

Answer 1: 51A
Answer 2: 58A
Answer 3: 65A
Answer 4: 80A

Answer 10

58A

Theory 21.5(B)

Question 11

Dual-voltage ac motors are made with two field windings. The field windings are connected in _____ for low-voltage operation and in _____ for high-voltage operation.

Answer 1: series, parallel
Answer 2: parallel, series
Answer 3: series, series
Answer 4: parallel, parallel

Answer 11

parallel, series

Theory 21.6(A)

Question 12

For a dual-voltage 230/460V motor, the field windings are connected in parallel for _____ operation and in series for _____ operation.

Answer 1: 230V, 460V
Answer 2: 460V, 230V
Answer 3: 230V, 230V
Answer 4: 460V, 460V

Answer 12

230V, 460V

Theory 21.6(A)

Question 13

When a motor is connected to the lower voltage rating for a 115/230V or 230/460V motor, the current rating will be _____ the current rating than if it is connected to the higher voltage rating.

Answer 1: half
Answer 2: twice
Answer 3: triple
Answer 4: none of these

Answer 13

twice

Theory 21.6(A)(1)(b)

Question 14

Whether a dual-voltage motor is connected to the high or low voltage, the _____ of the motor will remain the same.

Answer 1: voltage
Answer 2: current
Answer 3: resistance
Answer 4: volt-amperes

Answer 14

volt-amperes

Theory 21.6(A)(2)

Question 15

The volt-amperes for a 3 hp, 230V, single-phase motor with a nameplate rating of 15A is _____.

Answer 1: 3,450 VA
Answer 2: 6,670 VA
Answer 3: 8,990 VA
Answer 4: 9,000 VA

Answer 15

3,450 VA

Theory 21.6(A)(2)

Question 16

The volt-amperes for a 7.50 hp, 115V, single-phase motor with a nameplate rating of 75A is _____.

Answer 1: 5,450 VA
Answer 2: 6,675 VA
Answer 3: 8,625 VA keyboard_backspace correct
Answer 4: 9,090 VA

Question 17

Three-phase ac _____ motors are used in almost all major industrial applications.

Answer 1: wound-rotor
Answer 2: slip-ring induction
Answer 3: synchronous
Answer 4: squirrel-cage induction

Answer 17

squirrel-cage induction

Theory 21.8(A)

Question 18

In a(an) _____ motor, the rotor is locked in step with the rotating stator field and is dragged along at the speed of the rotating magnetic field.

Answer 1: wound-rotor
Answer 2: induction
Answer 3: synchronous
Answer 4: squirrel-cage

Answer 18

synchronous

Theory 21.8(B)

Question 19

_____ induction motors are used only in special applications because of their complexity.

Answer 1: Wound-rotor
Answer 2: Universal
Answer 3: Synchronous
Answer 4: Squirrel-cage

Answer 19

Wound-rotor

Theory 21.8(C)

Question 20

_____ motors are fractional horsepower motors that operate equally well on ac and dc and are used for vacuum cleaners, electric drills, mixers, and light household appliances.

Answer 1: Alternating-current
Answer 2: Universal
Answer 3: Wound-rotor
Answer 4: Synchronous

Answer 20

Universal

Theory 21.8(D)

Question 21

A generator produces electrical energy by converting mechanical energy from a _____.

Answer 1: heat source
Answer 2: prime mover
Answer 3: solar PV system
Answer 4: chemical activity

Answer 21

prime mover

Theory 22.2

Question 22

_____ is created by a generator when the electromagnetic field of the rotor cuts through the stator winding.

Answer 1: Voltage
Answer 2: Current
Answer 3: Resistance
Answer 4: Power

Answer 22

Voltage

Theory 22.3(A)(1)

Question 23

The approximate output current for a three-phase, 48 kVA, 120/208V generator is _____.

Answer 1: 100A
Answer 2: 110A
Answer 3: 125A
Answer 4: 130A

Answer 23

130A

Theory 22.4

Question 24

_____ voltage can originate from a single-phase generator.

Answer 1: Single-phase
Answer 2: Three-phase
Answer 3: Single-phase or Three-phase
Answer 4: none of these

Answer 24

Single-phase

Theory 22.5(A)

Question 25

Voltages in a three-phase circuit originate from a _____ where the voltage of each phase wire is out-of-phase with each other by 120˚.

Answer 1: generator
Answer 2: transformer
Answer 3: motor
Answer 4: all of these

Answer 25

generator

Theory 22.5(B)

Question 26

The _____ voltage at any point in the electrical system is the voltage that is measured by a voltmeter.

Answer 1: actual
Answer 2: nominal
Answer 3: equipment
Answer 4: utility

Answer 26

actual

Theory 22.6(C)

Question 27

In accordance with ANSI C84.1, the minimum voltage at the _____ cannot be less than 90 percent of the nominal system voltage.

Answer 1: service
Answer 2: utility
Answer 3: equipment
Answer 4: none of these

Answer 27

equipment

Theory 22.6(D)(1)

Question 28

In accordance with the NEMA MG1-standard, the minimum voltage at a motor cannot be less than 90 percent of the motor’s nameplate _____ rating.

Answer 1: voltage
Answer 2: starting current
Answer 3: locked-rotor
Answer 4: none of these

Answer 28

voltage

Theory 22.6(D)(2)

Question 29

An electromagnetic _____ uses electromagnetism to open or close a contact.

Answer 1: motor
Answer 2: generator
Answer 3: transformer
Answer 4: relay

Answer 29

relay

Theory 23.2(A)

Question 30

Normally _____ means the contacts are closed when the coil is de-energized.

Answer 1: open
Answer 2: closed
Answer 3: powered
Answer 4: none of these

Answer 30

open

Theory 23.3(B)

Question 31

When the relay coil is energized, the NC contacts _____ and the NO contacts _____.

Answer 1: open, close
Answer 2: close, open
Answer 3: open, open
Answer 4: close, close

Answer 31

open, close

Theory 23.3(C)

Question 32

Both the primary and secondary windings are wound on the same iron core, so the electromagnetic field from the primary winding cuts the secondary winding, which induces a voltage on the _____.

Answer 1: primary
Answer 2: secondary
Answer 3: motor
Answer 4: generator

Answer 32

secondary

Theory 24.4

Question 33

The _____ on the secondary winding is a function of the number of secondary wire loops cut by the primary electromagnetic field.

Answer 1: resistance
Answer 2: current
Answer 3: voltage
Answer 4: power

Answer 33

voltage

Theory 24.5

Question 34

The relationship of the number of turns of wire on the _____ as compared to the number of turns on the _____ is called the transformer winding turns ratio.

Answer 1: primary, secondary
Answer 2: secondary, primary
Answer 3: primary, primary
Answer 4: secondary, secondary

Answer 34

primary, secondary

Theory 24.6(A)

Question 35

A transformer has a primary winding of twenty turns and a secondary of ten turns. The winding turns ratio of this transformer is _____.

Answer 1: 2:1
Answer 2: 4:1
Answer 3: 5:1
Answer 4: 10:1

Answer 35

2:1

Theory 24.6(A)

Question 36

The secondary voltage of a 4:1 turns ratio transformer is _____ if the primary is 240V.

Answer 1: 60V
Answer 2: 210V
Answer 3: 208V
Answer 4: 277V

Answer 36

60V

Theory 24.6(C)

Question 37

If the primary and secondary windings of a transformer have the same number of wire loops (turns), the secondary output voltage will be the same as the primary input voltage. This type of transformer is called a(an) _____ transformer.

Answer 1: insulation
Answer 2: special
Answer 3: auto
Answer 4: isolation

Answer 37

isolation

Theory 24.7

Question 38

Autotransformers use a _____ winding for both the primary and secondary and are often referred to as buck-boost transformers.

Answer 1: different
Answer 2: special
Answer 3: separate
Answer 4: single

Answer 38

single

Theory 24.8

Question 39

The primary electromagnetic field induces a voltage in the secondary. As the secondary current flows, it produces an electromagnetic field that reduces the strength of the primary flux lines. This results in an increase in _____ current.

Answer 1: primary
Answer 2: secondary
Answer 3: tertiary
Answer 4: none these

Answer 39

primary

Theory 24.10

Question 40

Current flow in a secondary transformer winding creates an electromagnetic field that opposes the primary electromagnetic field resulting in less primary CEMF. The primary current automatically increases in direct proportion to the _____ current.

Answer 1: primary
Answer 2: secondary
Answer 3: tertiary
Answer 4: none these

Answer 40

secondary

Theory 24.10

Question 41

What is the secondary current for a fully loaded three-phase, 75 kVA, 480V to 208Y/120V transformer?

Answer 1: 104A
Answer 2: 140A
Answer 3: 208A
Answer 4: 500A

Answer 41

208A

Theory 24.11(A)

Question 42

The secondary current for a fully loaded single-phase, 37.50 kVA, 480V to 240V transformer is _____.

Answer 1: 145A
Answer 2: 156A
Answer 3: 162A
Answer 4: 169A

Answer 42

156A

Theory 24.11(A)

Question 43

What is the primary current for a fully loaded single-phase, 25 kVA, 480V to 240V transformer?

Answer 1: 52A
Answer 2: 72A
Answer 3: 82A
Answer 4: 614A

Answer 43

52A

Theory 24.11(B)

Question 44

What is the primary current for a fully loaded three-phase, 75 kVA, 480V to 208Y/120V transformer?

Answer 1: 10A
Answer 2: 70A
Answer 3: 80A
Answer 4: 90A

Answer 44

90A

Theory 24.11(B)

Question 45

The primary current for a fully loaded three-phase, 37.50 kVA, 480V to 208Y/120V transformer is _____.

Answer 1: 45A keyboard_backspace correct
Answer 2: 55A
Answer 3: 65A
Answer 4: 75A

Question 46

_____ transformers contain a primary and a secondary mounted on a single laminated iron core.

Answer 1: Single-phase
Answer 2: Two-phase
Answer 3: Three-phase
Answer 4: none these

Answer 46

Single-phase

Theory 24.12(A)

Question 47

_____ transformers are constructed of three sets of single-phase windings that are connected together to create a three-phase system.

Answer 1: Single-phase
Answer 2: Two-phase
Answer 3: Three-phase
Answer 4: none these

Answer 47

Three-phase

Theory 24.12(B)

Question 48

The _____ windings of a three-phase delta/wye-connected transformer are connected end-to-end with each other.

Answer 1: primary
Answer 2: secondary
Answer 3: low
Answer 4: high

Answer 48

primary

Theory 24.13(A)

Question 49

The _____ windings of a three-phase delta/wye-configured transformer have one end of each winding connected to a common point.

Answer 1: primary
Answer 2: secondary
Answer 3: middle
Answer 4: center

Answer 49

secondary

Theory 24.13(B)

Question 50

In a delta/wye 4-wire system, the voltage between any two primary wires is called “primary _____ voltage,” while the voltage between any two secondary wires is called “secondary _____ voltage.”

Answer 1: line-to-neutral, line-to-neutral
Answer 2: line-to-line, line-to-line
Answer 3: minimum, minimum
Answer 4: maximum, maximum

Answer 50

line-to-line, line-to-line

Theory 24.13(C)(1)

Question 51

_____ voltage is the voltage between a phase wire and a neutral wire in a delta/wye 4-wire system.

Answer 1: Line-to-neutral
Answer 2: Line-to-line
Answer 3: Neutral
Answer 4: Line

Answer 51

Line-to-neutral

Theory 24.13(C)(2)

Question 52

The _____ circuit wires of a three-phase delta/delta (high-leg) transformer are connected to each point where the winding leads meet.

Answer 1: primary
Answer 2: secondary
Answer 3: low
Answer 4: high

Answer 52

primary

Theory 24.14(A)

Question 53

The load wires of a three-phase delta/delta (high-leg) transformer are connected to each point where the _____ winding leads meet.

Answer 1: primary
Answer 2: secondary
Answer 3: low
Answer 4: high

Answer 53

secondary

Theory 24.14(B)

Question 54

In a delta/delta high-leg 4-wire system, the voltage between any two primary wires is known as the “_____ line-to-line voltage,” while the voltage between any two secondary wires is referred to as the “_____ line-to-line voltage.”

Answer 1: primary, primary
Answer 2: secondary, secondary
Answer 3: primary, secondary
Answer 4: secondary, primary

Answer 54

primary, secondary

Theory 24.14(C)(1)

Question 55

The line-to-neutral voltage is the voltage between a phase wire and the neutral wire. In a delta/delta high-leg 4-wire system, the Line 1- and Line 3-to-neutral voltage is 120V, and the Line 2-to-neutral will be _____.

Answer 1: 120V
Answer 2: 208V
Answer 3: 240V
Answer 4: 277V

Answer 55

208V

Theory 24.14(C)(2)