Theory Units 21-24 Flashcards
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
stator, rotor
Theory 21.2(A)
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
downward, upward
Theory 21.2(C)
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
80 hp
Theory 21.3
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
150 hp
Theory 21.3
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
3.75 kW
Theory 21.3
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
18.65 kW
Theory 21.3
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
rotor
Theory 21.4(B)
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
LRC
Theory 21.4(C)(2)
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
20A
Theory 21.5(B)
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
58A
Theory 21.5(B)
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
parallel, series
Theory 21.6(A)
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
230V, 460V
Theory 21.6(A)
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
twice
Theory 21.6(A)(1)(b)
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
volt-amperes
Theory 21.6(A)(2)
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
3,450 VA
Theory 21.6(A)(2)
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
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
squirrel-cage induction
Theory 21.8(A)
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
synchronous
Theory 21.8(B)
_____ 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
Wound-rotor
Theory 21.8(C)
_____ 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
Universal
Theory 21.8(D)
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
prime mover
Theory 22.2
_____ 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
Voltage
Theory 22.3(A)(1)
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
130A
Theory 22.4
_____ 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
Single-phase
Theory 22.5(A)
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
generator
Theory 22.5(B)
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
actual
Theory 22.6(C)
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
equipment
Theory 22.6(D)(1)
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
voltage
Theory 22.6(D)(2)
An electromagnetic _____ uses electromagnetism to open or close a contact.
Answer 1: motor
Answer 2: generator
Answer 3: transformer
Answer 4: relay
relay
Theory 23.2(A)
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
open
Theory 23.3(B)
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
open, close
Theory 23.3(C)
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
secondary
Theory 24.4
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
voltage
Theory 24.5
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
primary, secondary
Theory 24.6(A)
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
2:1
Theory 24.6(A)
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
60V
Theory 24.6(C)
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
isolation
Theory 24.7
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
single
Theory 24.8
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
primary
Theory 24.10
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
secondary
Theory 24.10
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
208A
Theory 24.11(A)
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
156A
Theory 24.11(A)
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
52A
Theory 24.11(B)
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
90A
Theory 24.11(B)
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
_____ 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
Single-phase
Theory 24.12(A)
_____ 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
Three-phase
Theory 24.12(B)
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
primary
Theory 24.13(A)
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
secondary
Theory 24.13(B)
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
line-to-line, line-to-line
Theory 24.13(C)(1)
_____ 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
Line-to-neutral
Theory 24.13(C)(2)
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
primary
Theory 24.14(A)
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
secondary
Theory 24.14(B)
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
primary, secondary
Theory 24.14(C)(1)
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
208V
Theory 24.14(C)(2)
