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