Chapter 8, Unit 21-24
The secondary current for a fully loaded single-phase, 37.5 kVA, 480 to 240V transformer is ______. (a) 68A (b) 156A (c) 88A (d) 98A
VA/E 37500/240V 156A
In accordance with the ANSI C84.1, the minimum voltage at the _________ cannot be less than 90 percent of the nominal system voltage. (a) service (b) utility (c) equipment (d) none of these
equipment
The load wires are connected to each point where the _______ winding leads meet. (a) primary (b) secondary (c) low (d) high
secondary
Three-phase ac _____ motors are used in almost all major industrial applications. (a) wound-rotor (b) induction (c) synchronous (d) squirrel-cage
squirrel-cage
A motor used opposing electromagnetic fields in order to rotated the motor shaft. The stationary electromagnetic field is created by the ______, and the rotating electromagnetic field is creaed by the _______. (a) stator, rotor (b) rotor, stator (c) winding A, winding B (d) none
stator, rotor
What size motor in horsepower is required to produce approximately 60 kW of output watts? (a) 50 hp (b) 60 hp (c) 70 hp (d) 80 hp
( 60 x 1,000/746W) = 80 hp
What is the nameplate FLA for a 5 hp, 230V, single phase motor with 93 percent power factor and 87 percent efficiency? (a) 10A (b)20A (c) 28A (d) 35A
Motor FLA Single Phase = (hp x 746W)/(E x Eff x PF) (5 x 746W)/(230V x .87 x .93) = 20A
What is the primary current for a fully loaded three-phase, 75 kVA, 480V to 208Y/120V transformer is _______. (a) 45A (b) 90A (c) 65A (d) 75A
Three Phase Primary Current = Transformer VA/(Volts x 1.732) 75,000/(480 x 1.732) 90A
______ 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. (a) alternating-current (b) universal (c) wound-rotor (d) synchronous
Universal
The primary current for a fully loaded three-phase, 37.5 kVA, 480V to 208Y/120V transformer is _______ (A) 45A (b) 55A (c) 65A (d) 75A
VA/(E x 1.32) 37500/(831.360) 45A
The ______ voltage at any point in the electrical system is the voltage that is measured by voltmeter. (a) actual (b) nominal (c) equipment (d) utility
actual
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." (a) insulation (b) special (c) auto (d) isolation
isolation
"Normally ______" means the contacts are closed when the coil is energized. (a) open (b) closed (c) powered (d) none
open
Autotransformers use a ______ winding for both the primary and secondary and are often referred to as "buck-boost transformers." (a) different (b) special (c) separate (d) single
single
________ transformers contain a primary and a secondary mounted on a single laminated iron core. (a) single phase (b) two phase (c) three phase (d) none
single phase
_______ voltage can originate from a single-phase generator. a) sing-phase b) three-phase c) single- phase or three-phase d) none
single-phase
The approx output for a three-phase, 48 kVA, 120/208V generator is ________. a) 100A (b) 110A (c) 125A (d) 130A
Three-Phase I = VA/(E x 1.732) = 48,000/(208 x 1.732) 48,000/360 = 130A
If the primary phase voltage is 480V and the secondary phase voltage is 240V, the voltage turns ratio is ________. (a) 1:2 (b) 1:4 (c) 2:1 (d) 4:1
Voltage Turns ratio = Primary volts: secondary volts 480/240 2:1
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 degree. (a) generator (b) transformer (c) motor (d) all of these
generator
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. (a) series, parallel (b) parallel, series (c) series, series (d) parallel, paralel
parallel, series
The ________ windings of a three-phase delta/wye connected transformer are connected end to end with each other. (a) primary (b) secondary (c) low (d) hight
primary
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. (a) primary (b) secondary (c) tertiary (d) none
primary
______ induction motors are used only in special applications because of their complexity. (a) wound-rotor (b) universal (c) synchronous (d) squirrel-cage
wound-rotor
What size motor in horsepower is required to produce approx 110kW of output watts? (a) 75 hp (b) 100 hp (c) 125 hp (d) 150 hp
(110kw x 1000/746W) = 150 hp
What is the approx output in watts of a 15 hp motor? (a) 11 kw (b) 15 kw (c) 22 kw (d) 31 kw
(15 x 746/1000) = 11 kw
What are the approx output in watts of a 25 hp? (a) 18.65 kW (b) 19.50 kW (c) 22.75 kW (d) 31.45 kW
(25 x 746/1000) = 18.65 kW
What size motor in horsepower is required to produce approximately 30 kW of output watts? (a) 20 hp (b) 30 hp (c) 40 hp (d) 50 hp
(30/746) x 1000 = 40 hp
What are the approx output watts of a 5 hp motor? (a) 3.75 kW (b) 4.75 kW (c) 6.75 kW (d) 7.75 kW
(5 x 746/1000) = 3.75 kw
Motors are used to convert electrical energy into mechanical work and the output mechanical work of a motor is rated in horsepower, were 1 hp = __________. (a) 476W (b) 674W (c) 746W (d) 840W
746W
The motor nameplate amperes rating is commonly referred to as the motor "_________." (a) FLA (b) FLC (c) LRA (d) any fo these
FLA - full load amps
A motor that operates at ________ will cause its windings to overheat to the point where the wire windings' insulation and lubrication will be damaged. (a) FLA (b) FLC (c) LRC (d) any of these
LRC - locked, rated, currents
What is the nameplate FLA for a 20 hp, 208V, three-phase motor with 90 percent power factor and 80 percent efficiency? (a) 51A (b) 58A (c) 65A (d) 80 A
Motor FLA, Three-Phase = (hp x 746W)/(E x 1.732 x Eff x PF) (20hp x 746)/(208 x 1.732 x .80 x.90) = 58A
The secondary voltage of a 4:1 turns ratio transformer is _______ if the primary is 240V. (a) 60V (b) 210V (c) 208V (d) 277V
Secondary Voltage = Primary Volts/Voltage Turns Ratio 240/4 60V
The secondary voltage of a 5:1 transformer is ______ of the primary is 240V (a) 6V (b) 12V (c) 24V (d) 48V
Secondary Voltage = Primary Volts/Voltage Turns Ratio 240/5 48V
What is the secondary current for a fully loaded single-phase, 25 kVA, 480V to 240V transformer? (a) 52A (b) 104A (c) 208A (d) 250A
Single Phase Secondary Current - Transformer VA / Volts 25,000/240V 104A
The approximate output current for a single-phase, 22 KVA, 240V generator is _______. (a) 50A (b) 70A (c) 90A (d) 100A
Single-Phase - I = VA/E 22 kva x 1000 =22,000 22,000 VA / 240V = 91.6A
What is the primary current for a fully loaded single-phase, 25 kVA, 480V to 240V transformer? (a) 52A (b) 72A (c) 82A (d) 614A
Single-Phase Primary Current = Transformer VA/Volts 25,000/480 52
The volt-amps for a 7.50 hp, 115V, single-phase motor with a nameplate rating of 75A is _______. (a) 5,450 VA (b) 6,675 VA (c) 8,625 VA (d) 9,090 VA
Single-Phase VA = Volts x Amps 115 x 75 = 8,625 VA
The volt-amperes for a 5 hp, 208V, single-phase motor with a nameplate rating of 28.50A is _______. (a) 4,250 VA (b) 5,928 VA (c) 8,991 VA (d) 9,289 VA
Single-Phase VA = Volts x Amps 208V x 28.5A = 5,928 VA
The volt-amperes for a 3 hp, 230V, single-phase motor with a nameplate rating of a 15A is ________. (a) 3,450 VA (b) 6,670 A (c) 8,990 VA (d) 9,000 VA
Single-Phase VA = Volts x Amps 230V x 15 = 3450
What is the secondary current for a fully loaded three-phase, 75 kVA, 480V to 208Y/120V transformer? (a) 104A (b) 140A (c) 208A (d) 500A
Three-Phase Secondary Current = Transformer VA/(Volts x 1.732) 75,000/(208 x 1.732) 208A
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. (a) downward, upward (b) upward, downward (c) spinning, static (d) none
downward, upward
The _____ of a generator depends on the number of stator poles and the speed of the rotor. (a) voltage (b) current (c) resistance (d) frequency
frequency
When a motor is connected to the higher 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 lower voltage rating. (a) half
half
Transformers are rated in _______. (a) henrys (b) kW (c) W (d) kVA
kVA
A generator produces electrical energy by converting mechanical energy from a "________." (a) heat source (b) prime mover (c) solar PV system (d) chemical activity
prime mover
Three-phase alternating-current generators have thee sets of equally spaced windings, each winding is ______ out of phase with each other. (a) 90 degrees (b) 120 degrees (c) 180 degrees (d) 240 degrees
120 degrees
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 _______. (a) 120V (b) 208V (c) 240V (d) 277V
208V
For a dual-voltage 230/460V motor, the field windings are connected in parallel for ________ operating and in series for _______ operation. (a) 230V, 460V (b) 460V, 230V (c) 230V, 230V (d) 460V, 460V
230V, 460V (parallel = low V and series = high V)
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. (a) voltage (b) starting current (c) locked-rotor (d) none of these
voltage
The _______ on the secondary winding is a function of the number of the secondary wire loops cut by the primary electromagnetic field. (a) resistance (b) current (c) voltage (d) power
voltage
The nameplate motor FLA rating describes the motor current rating when it carries its rated horsepower, rated ______, efficiency, and power factor. (a) power (b) resistance (c) CEMF (d) voltage
voltage
The relationship between primary voltage and secondary voltage is called the "transformer "____________ turns ratio." (a) winding (b) voltage (c) power (d) ampere
voltage
The _____ windings of a three-phase delta/wye-configured transformer have one end of each winding connected to a common point. (a) primary (b) secondary (c) middle (d) center
secondary
The voltage between any two primary wires is called "primary ______ voltage," while the voltage between any two secondary wires is called "secondary ________ voltage." (a) line-to-neutral, line-to-neutral (b) line to line, line to line (c) minimum, minimum (d) maximum, maximum
line to line, line-to-line
Swapping any ______ of the line wires can revere a three-phase ac motor's rotation. (a) one (b) two (c) three (d) four
two
Whether a dual-voltage motor is connected to the high or low voltage, the ________ of the motor will remain the same. (a) voltage (b) current (c) resistance (d) volt-amperes
volt-amperes
_______ is created by a generator when the electromagnetic field of the rotor cuts through the stator winding. (a) voltage (b) current (c) resistance (d) power
voltage
_____ voltage is the voltage between a phase wire and a neutral wire. Answer 1: Line-to-neutral Answer 2: Line-to-line Answer 3: Neutral Answer 4: Line
line-to-neutral
The ______ system voltage is a voltage used for circuit calculations. (a) actual (b) nominal (c) equipment (d) utility
nominal
"Normally _______" means that the contacts are open when the coil is de-energized. (a) open (b) closed (c) powered (d) none
open
When the relay coil is energized, the NC contacts __________ and the NO contacts ________. (a) open, close (b) close, open (c)open, open (d) close, close
open, close
The _____ circuit wires are connected to each point where the winding leads meet. (a) primary (b) secondary (c) low (d) high
primary
The relationship of the number of turns of wire on the _______ as compared to the number of the turns on the _______ is called the transformer "winding turns ratio." (a) primary, secondary (b) secondary, primary (c) primary, primary (d) seconddary, secondary
primary, secondary
The transformer winding that is connected to the source is called the "__________" winding and the transformer winding that is connected to the load is called the "_______" winding. (a) secondary, primary (b) primary, secondary (c) high-leg, low-leg (d) none of these
primary, secondary
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." (a) primary, primary (b) secondary, secondary (c) primary, secondary (d) secondary, primary
primary, secondary
An electromagnetic _________ uses electromagnetism to open or close a contact. (a) motor (b) generator (c) transformer (d) relay
relay
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 _____. (a) stator (b) rotor (c) shaft (d) any of these
rotor
When a motor starts, the currents drawn is between six and ten times the motor's nameplate _______. (a) lock-rotor ameres (b) running amperes (c) voltage (d) none of these
running amperes
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 _________. (a) primary (b) secondary (c) motor (d) generator
secondary
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. (a) primary (b) secondary (c) tertiary (d) none
secondary
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. (a) wound-rotor (b) induction (c) synchronous (d squirrel-cage
synchronous
_______ transformers are constructed of three sets of single-phase windings that are connected together to create a three-phase system. (a) single phase (b) two phase (c) three phase (d) none
three phase
In an ac induction motor, the stator produces rotating magnetic field that induces current in the rotor windings. The rotor current generates a magnetic field in opposition to the magnetic filed of the stator, thereby causing the motor to _______. (a) explode (b) turn (c) jam (d) lock p
turn
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 lower voltage rating. (a) half (b) twice (c) triple (d) none of these
twice
In accordance with ANSI C84. 1, the ________ voltage must be no more than 105 percent and not less than 90 percent of the nominal voltage. (a) transformer (b) generator (c) equipment (d) utility
utility
A transformer has a primary winding of twenty turns and a secondary of ten turns. The winding turns ratio of this transformer is _______. (a) 2:1 (b) 4:1 (c) 5:1 (d) 10:1
winding turns ratio = Primary turns:secondary turns 20/10 2:1
