Electrical Power/Machinery Final
generator
"Alternator" is another name for an AC ___.
True
A 1φ induction motor is comparable to a transformer.
six
A 3φ generator has ___ leads coming from the armature windings.
delta
A ___ connection is a connection that has each coil connected end-to-end to form a closed loop.
balun
A ___ is a special radio frequency transformer used to match impedance between a balanced 2-wire transmission line to an unbalanced transmission line or component.
power quality meter
A ___ is a test instrument that measures, displays, and records voltage, current, and power, as well as power problems such as sags, swells, transients, and harmonics.
soft
A ___ neutral position is a position where the brushes are aligned 90° from the stator poles.
shaded
A ___ pole is a single pole, normally made of a single turn of heavy-gauge copper wire, used for starting a single-phase motor.
False
A balun is a type of buck-boost transformer.
True
A cage rotor is sometimes referred to as a "squirrel-cage rotor".
start-and-run
A capacitor-____________________ motor has the most running torque of all the capacitor-style motors.
capacitors
A common method for correcting the power factor of a circuit is to connect ___ across the load.
armature
A compensation winding is an inductor used to reduce ___ reactance effects.
diode
A flywheel ___ is used in an alternator to suppress the inductive voltage that occurs when the exciter switch is opened.
False
A multiple-winding transformer has more than four windings on its core.
False
A neutral line is required for a properly balanced 3φ load.
True
A potential transformer is a type of instrument transformer.
False
A power quality meter is used to analyze circuits by measuring the true power in a 3φ system.
increase current levels
A power-correcting capacitor does all of the following except ___.
True
A rotor is the rotating part of an AC motor.
field coil
A salient pole is a pole that consists of a separate radial projection having its own iron pole and ____________________.
True
A split-phase motor is a single-phase AC motor with a running winding and a starting winding.
False
A synchronous motor is a 1φ motor that runs at synchronous speed.
electromagnetism
A transformer is an electrical device that uses ___ to change voltage from one level to another or to isolate one voltage from another.
True
A variable resistance is connected in series with rotor windings of a wound rotor to limit inrush current.
True
A wall transformer has prongs for connection to an electrical receptacle.
True
A wye connection is sometimes referred to as a star connection.
True
A wye-connected generator has line voltages that are equal in value.
X
A(n) "___" indicates low-voltage leads.
reactive
A(n) ___ circuit is either capacitive or inductive and has a power factor of less than 1.
wye
A(n) ___ connection is a connection that has one end of each coil connected together and the other end of each coil left open for external connections.
rectifier
A(n) ___ is a device that converts AC voltage to DC voltage by allowing the AC voltage and current to flow in only one direction.
armature
A(n) ___ is a movable coil of wire in a generator that rotates relative to the magnetic field.
stator
A(n) ___ is a part of a generator that remains in a stationary position.
wattmeter
A(n) ___ is a test instrument that is used to measure true power in a circuit.
pole
A(n) ___ is the number of completely isolated circuits that a relay can switch.
brush
A(n) ___ is the sliding contact that rides against the slip rings and is used to connect the armature to the external circuit.
repulsion
A(n) ___ motor is a motor with the rotor connected to the power supply through brushes that ride on the commutator.
swamping
A(n) ___ resistor is a resistor that is used to suppress the high inductive kick of an exciter current.
centrifugal
A(n) ___ switch opens to disconnect the starting winding when the rotor reaches a preset speed and reconnects when the speed falls below a set value.
isolation
A(n) ___ transformer has equal primary and secondary voltages and is used to electrically separate the source from the load.
potential
A(n) ___ transformer is a precision two-winding transformer that is used to step down high voltage to allow safe voltage measurement.
core-type
A(n) ___ transformer is a transformer that has windings placed around each leg of the core material.
cage rotor
A(n) ____________________ consists of a series of parallel copper or aluminum bars placed in slots on the rotor core.
capacitor-start-and-run
A(n) ____________________ motor (dual-capacitor motor) uses two capacitors.
universal
A(n) ____________________ motor is an AC series motor with brushes and a wound armature.
hard neutral
A(n) ____________________ position is a position where brushes are aligned directly with stator poles.
power
A(n) ____________________ transformer is used to raise or lower voltage as required to serve transmission circuits.
radio frequency
A(n) ____________________ transformer is used to transfer energy in narrow frequency bands from one circuit to another.
kVa
AC generators are rated in ___
True
An AC generator cannot produce output voltage before the rotor has been excited.
windings
An autotransformer is a transformer in which the primary and secondary circuits have portions of their two ___ in common.
electrical
An isolation transformer has complete ____________________ separation between the primary and secondary windings.
True
Appliances that produce heat or provide incandescent light are examples of resistive loads.
False
As slip increases, torque decreases.
False
Because core-type transformers use more iron in the core than other transformers, they are usually more expensive.
True
Buck-boost transformers can lower or raise line voltage.
10
Capacitor motors range in size from Z\, HP to ____________________ HP.
False
Centrifugal switches are required in capacitor-run motors.
True
Changing any two connections of a 3φ motor will cause the rotation of the magnetic field to reverse.
False
Clamp-on ammeters measure current by measuring the strength of the voltage around a single conductor.
True
Current flow through the windings of a transformer can generate heat loss.
secondary
Current ratings in a transformer are usually specified for the ____________________ windings only.
90
Currents lag their respective voltages by ___°.
True
Each branch of a delta connection has the same value of impedance.
magnetic lines of force
Flux loss occurs when some of the ____________________ from the primary winding do not travel through the core to the secondary winding.
1.15
For 3φ and 1φ power systems to deliver the same amount of power to their respective loads, a 1φ power system requires about ___ times the copper required for a 3φ power system.
False
General voltage is a voltage produced around a closed path or circuit by a change in the magnetic lines of force linking the path.
False
Generated voltages in a delta-connected generator have different values from the load voltages.
1:5
If a transformer has voltage of 120 V across the primary winding and voltage of 600 V across the secondary winding, it is a step-up transformer, and the turns ratio is equal to ____________________.
False
If the centrifugal switch of a split-phase motor opens, the windings will overheat and destroy the motor.
step-down
If the turns ratio of primary to secondary windings is 2:1, the transformer is a(n) ____________________ transformer.
True
Impedance matching adjusts the load-circuit impedance to produce the desired energy transfer from the power source to the load.
load
Impedance matching is also known as ___ matching.
False
In a capacitive reactive circuit, voltage leads the current.
True
In a hard neutral position, a rotating magnetic field is not present.
True
In a step-up transformer, current is stepped down.
120°
In a three-phase power system, the voltage of each conductor is ___ out of phase with that of the other conductors.
X
In a transformer schematic symbol, an "H" indicates the primary winding and a(n) "____________________" indicates the secondary winding.
False
In a wye connection, five leads are connected together, while the other five leads are brought out for connecting to the load.
starting
In the construction of a capacitor motor, a capacitor is connected in series with the ___ winding.
True
Increasing voltage and reducing current in a system can reduce the cost of power lines.
False
Induced currents in an iron core are desirable because they produce heat and use power.
False
Less maintenance is required for a 1φ motor than for a 3φ motor.
torque
Limiting inrush current gives a motor greater startup ____________________ at a lower startup current.
True
Loads can be both inductive and resistive.
direction
Magnetic polarity is based on the ____________________ of current flow.
90
Maximum induced voltage occurs when the conductor cuts the field at ___°.
slip
Metallic rings that are connected to the ends of the armature and are used to connect the induced voltage to the brushes are known as ___ rings.
False
Most transformers have only one winding.
coefficient of coupling
Mutual inductance, the measure of efficiency with which power is transferred between windings, is also known as ___.
True
One advantage of using an autotransformer rather than other types of power transformers is that current flow through the windings is reduced.
False
Overheating of a transformer often occurs when the transformer is operating above its secondary voltage.
factor
Power ___ is the ratio of true power used in an AC circuit to apparent power delivered to the circuit.
90
Power factor correction is the process of correcting power factor to at least ___%.
in phase
Power factor is ___ for a resistive load.
90
Power transformers should be loaded to close to ___% of their rated power.
before the electric motor drive
Power-correcting capacitors must be placed ___.
False
Repulsion motors should always be started from the soft neutral position.
False
Shaded-pole motors can have either a leading or lagging power factor, which makes them ideal for use in power factor correction.
False
Single-phase power creates smoother DC output with less filtering than three-phase power.
True
Split-phase motors can operate with two separate voltages.
False
Synchronous motors are self-starting.
60
The United States and Canada use a power distribution frequency of ___ Hz.
pitch
The ___ of a coil is how tightly the windings of a coil are wound.
reflected
The ____________________ load of a transformer is the primary impedance of the transformer that is directly proportional to the secondary load.
inductive
The ____________________ method of reducing armature reactance is used with DC motors only.
stator windings
The armature of a motor will only turn when it is in the rotating magnetic field caused by the ____________________.
True
The frequency at which a transformer operates determines its classification.
True
The greater the number of poles, the greater the frequency of the generated voltage.
False
The higher the power factor, the higher the operating cost.
True
The line currents of a delta-connected generator have equal values and are located 120° apart.
hysteresis
The property where the magnetic induction of a winding lags the magnetic field that is charging the winding is known as ____________________.
False
The turns ratio is the ratio of the number of turns in the secondary winding to the number of turns in the primary winding.
wound
The two types of rotors used on AC motors are the cage rotor and the ___ rotor.
parallel
The windings of a split-phase motor are connected in ____________________.
multiple-horsepower
Three-phase (3φ) induction motors are typically used to turn ___ loads.
False
Three-phase motors require more components to operate and often require more maintenance than 1φ motors.
True
Three-phase power is often preferred to single-phase power because less copper is used to deliver a given amount of power.
conductors
Three-phase power systems use three individual ___ to transmit power.
watts
Transformer OEMs typically specify transformer power ratings in ____________________.
False
Transformer efficiency is the ratio of the output current to the input current.
True
Voltage across any winding of a transformer has polarity.
True
Voltage and current ratings of a transformer must be known to calculate power ratings.
True
When a transformer is connected to an inductive-resistive-capacitive load, the circuit is purely resistive at resonance.
1.73
When magnitudes are equal and 120° apart, the resultant vector can be obtained by multiplying one vector by ___.
45
When resistance equals inductive reactance in each phase, current lags source voltage by ___°.
lower initial cost
Which of the following is not an advantage of a wound-rotor induction motor over a cage motor?
motor under full load
Which of the following is not an example of an inductive load?
wye
Wound-rotor windings are typically ____________________-connected.
Generators
___ are used to produce three-phase power.
Excitation
___ current is the DC used to produce electromagnetism in the fields of a DC motor or generator or in the rotor of an AC generator.
Plugging
___ is a method of motor braking in which the motor connections are reversed so that the motor develops a countertorque that acts as a braking force.
Slip
___ is the difference between the synchronous speed and the actual speed of a motor.
Jogging
___ is the frequent starting and stopping of a motor for short periods.
Flux
___ loss is a power loss that occurs in a transformer when some of the magnetic lines of force from the primary winding do not travel through the core to the secondary winding.
Resistive
___ loss is power loss in a transformer caused by the resistance of the copper conductors used to make the windings.
Eddy current
___ loss is power loss in a transformer or motor due to currents induced in the metal field structure from the changing magnetic field.
Generated
___ voltage is a voltage produced in a closed path or circuit by the relative motion of the circuit or its parts with respect to magnetic lines of force.
Flux linkage
____________________ is the number of flux lines linking the primary and secondary transformer windings.
Critical coupling
____________________ is the point separating a tight coefficient of coupling from a loose coefficient of coupling.
Reflected impedance
____________________ is the primary-load impedance that is proportional to the secondary-load impedance.
Synchronous speed
____________________ is the theoretical speed of a motor based on line frequency and the number of poles of the motor.
Volts per turn
____________________ is the voltage dropped across each turn of a winding or the voltage induced into each turn of the secondary winding.
Split-phase
____________________ motors are commonly used to operate washing machines, oil burners, small pumps, and blowers.