2B Midterm
The _____ ride against the commutator segments and are used to connect the armature to the external circuit of the DC machine.
brushes
The motor that does not contain a wound armature, commutator, or brushes is the _____ motor.
brushless DC
In a transformer, even when there is no load connected, there will be some small current flow known as _____ current.
excitation
When using an open delta with a center tapped transformer, one wire is the high leg. The high leg is the one that _____. Correct!
has the highest voltage
Permanent magnet motors have _____ efficiency than conventional field-wound motors.
higher
The output winding of a transformer is called the _____ winding.
secondary
The series generator has only a series field, which is connected in _____ with the armature.
series
In a generator, the _____ permits part of the current that normally flows through the series field to flow through the resistor.
series field shunt rheostat
Small permanent magnet motors that have lightweight rotors are often used as _____.
servomotors
Three-phase voltages are _____ out of phase with each other.
120
transformer has a 2:1 turns ratio. 120 V is applied to the primary. What is the secondary voltage?
60
In a balanced three-phase system, the conductors need be only about _____ the size of conductors for a single-phase, two-wire system of the same kilovolt-ampere (kVA) rating
75%
A wye-connected secondary has a phase voltage of 277.14 V. What is the line voltage?
480
Armatures are wound to provide high voltage, high current, or some specific combination of voltage and current. Which type of winding provides low voltage and high current?
Lap wound
Line current and phase current are the same in the _____ configuration
Wye
Series field windings are connected in series with the armature. They are wound with _____ turns of fairly _____ wire.
few, large
Most transformer cores are assembled from many thin sheets of metal. This type of construction is called _____.
laminated
A delta connected set of windings has a phase voltage of 100 V. What is the line voltage?
100
A delta connected set of windings has a phase voltage of 480 V. What is the line voltage?
480
What type of core is often found on high-voltage distribution transformers?
H type ?
The rotating part of a generator is called the _____.
armature
A tape-wound core is also called a(n) _____ core.
toroid
A delta-delta transformer has a primary voltage of 7200 V and a secondary voltage of 360 V. What is the turns ratio?
20:1
A square wave voltage varies between 0 V and 12 V. The positive pulses are 25 μs wide and there is a 75 μs gap between them. What is the DC average of the waveform?
3v
A wye-delta transformer has a turns ratio of 2:1. It has a secondary line voltage of 480 V. The secondary is connected to a wye-connected three-phase resistive load of 50 Ω in each phase. What is the current flow is in each load resistor?
5.54 A
A square wave voltage varies between 0 V and 12 V. The positive pulses are 50 μs wide and there is a 50 μs gap between them. What is the DC average of the waveform
6 v
A delta-wye transformer has a turns ratio of 9:1. The primary line voltage is 3600 V. What is the secondary line voltage
692.8 v
A wye-delta transformer has a primary line voltage of 7200 V and a secondary line voltage of 480 V. What is the turns ratio? Correct!
8.66-1
An open delta transformer is assembled from two 50 kVA transformers. The output power of the open delta is _____.
86.6 kVA
A square wave voltage varies between 0 V and 12 V. The positive pulses are 75 μs wide and there is a 25 μs gap between them. What is the DC average of the waveform?
9 v
A delta-connected set of windings has a phase current of 10 A. What is the line current?
17.32 A
A transformer has a 240 V primary and a 60 V secondary. With a 5 ohm load connected, what is the primary current?
3 A
In three-phase power systems, the delivered power _____.
never falls to zero
In calculating apparent power (VA) in a three-phase circuit, the phase values of voltage and current are multiplied by _____.
three
An isolation transformer has the same input and output voltages.
true
What is a magnetically operated device that can change values of voltage, current, and impedance without changing frequency?
a transformer
_______________ is the twisting or bending of the magnetic lines of flux of the pole pieces. You Answered
armature reaction
What is the component of a DC generator that converts the armature AC into DC?
commutator
When a DC machine is used as a generator, the _______________ performs the function of a mechanical rectifier to change the AC produced in the armature into DC before it exits the machine through the brushes.
commutator
The compound motor connection that should generally be avoided is the _____.
differential
The transformer that converts a high voltage from the power company down to 240/120 V for homes and businesses is called a(n) _____ transformer.
distribution
A series motor may be operated with no load connected.
false
When single-phase loads are tied to a three-phase transformer, the phase currents of the transformer will be automatically balanced.
false
The alternator must supply the _____ for each of the loads.
line current
In a three-phase connection, what is the voltage measured between the lines?
line voltage
A transformer supplying a house with 240/120 V has a secondary which is center tapped. The conductor connected to the center is called the _____ conductor.
neutral
When calculating the power of a pure resistive load, the voltage and current are in phase with each other and the power factor is _____.
one
Counter-electromotive force (CEMF) and back-EMF are names for the voltage induced into the armature of a DC motor.
true
A three-phase connection in which three separate inductive loads have been connected together is a(n) _____ connection
Delta
The servomotor featuring a fiberglass and copper rotor is the _____ motor.
ServoDisc
Shunt generators contain only a shunt field winding connected in _____ with the armature.
parallel
In a three-phase connection, what is the voltage measured across a single winding?
phase voltage
A wye-delta transformer has its _____ connected as a wye and its _____ connected as a delta.
primary secondary
The DC motor, known as a "constant speed motor," is the _____ motor.
shunt
When the field winding of a DC motor is connected in parallel with the armature, the motor is called a _____ motor.
shunt
A transformer in which the secondary voltage is more than the primary voltage is called a(n) _____ transformer.
step up
The industrial use transformer that normally has 240 V or 480 V primary and a 120 V secondary is called a(n) _____ transformer.
to control
A transformer in which the secondary voltage is less than the primary voltage is called a(n) _____ transformer.
to step down
A compound generator has both series and shunt field windings. When those windings are connected so their fields oppose each other in the production of magnetism, that connection is called _____.
Differential compound
A compound generator has both series and shunt field windings. When those windings are connected so they aid each other in the production of magnetism, that connection is called _____.
cumulative compound
The output voltage of a generator is usually controlled by the amount of _____.
Field excitation current
Armatures are wound to provide high voltage, high current, or some specific combination of voltage and current. Which type of winding provides high voltage and low current?
Wave wound
The three-phase connection in which one end of each of the windings are connected together is called a(n) _____ connection.
Wye
A transformer that has one winding, which is used for both the primary and secondary, is called a(n) _____.
autotransformer
A generator containing both series and shunt fields is called a _____ generator.
compound
The relationship of the strengths of the two fields in a generator determines the amount of _____.
compounding
When a motor is connected differential compound, the _____ determines the direction of rotation of the motor at no load or light load.
Shunt field
In a three-phase circuit, the true power (watts) is found by
multiplying apparent power by the power factor
In a transformer, the turns of primary wire compared to the turns of secondary wire is called the _____ ratio.
turns
A tape-wound core is assembled by _____.
winding a long continuous tape into a spiral
Line voltage and phase voltage are the same in the _____ connection.
Delta
Armatures are wound to provide high voltage, high current or some specific combination of voltage and current. Which type of winding provides moderate voltage and moderate current?
frogleg-wound
What is a device that converts mechanical energy into DC electrical energy?
generator
A compound motor has _____ field windings.
Series and shunt
A device that converts electrical energy into mechanical energy is called a(n) _____.
motor
A wye-delta transformer has a turns ratio of 2:1. It has a secondary line voltage of 480 V. The secondary is connected to a wye-connected three-phase resistive load of 50 Ω in each phase. What is the primary line current?
1.6
A wye-delta transformer has a turns ratio of 2:1. It has a secondary line voltage of 480 V. The secondary is connected to a wye-connected three-phase resistive load of 50 Ω in each phase. What is the primary phase current?
1.6
A wye-delta transformer has a primary voltage of 7200 V and a secondary voltage of 360 V. What is the turns ratio?
11.55-1
The horsepower rating of three-phase motors and the kilovolt-ampere rating of three-phase transformers are about _____ greater than for single-phase motors or transformers with a similar frame size.
150%
A wye-delta transformer has a turns ratio of 2:1. It has a secondary line voltage of 480 V. The secondary is connected to a wye-connected three-phase resistive load of 50 Ω in each phase. What is the secondary phase current?
3.2
A delta-connected three-phase alternator is driving a wye-connected resistive load. The alternator output voltage is 480 V. The load resistors are 12 Ω each. What is the phase current in the alternator?
40 A
A wye-delta transformer has a secondary phase voltage of 480 V. A delta-connected resistive load has a resistance of 12 Ω in each leg. What is the current in each load leg?
40 A
In a compound DC motor control circuit, the field loss relay will disconnect the _____ if power is lost to the _____.
Armature, shunt field
In an open delta with single-phase loads, the high leg must be identified by _____.
Both A and B
What provide(s) the magnetic field necessary for the operation of a DC machine?
Pole pieces
What function is performed by dielectric oil?
all above
_______________ is a measure of the useful electric energy produced by the generator. You Answered
countertorque
Any transformer flux that does not follow the core and escapes into the surrounding air is called _____.
flux leakage
The amount of current that flows into a transformer primary when voltage is first applied is called _____ current.
inrush
A transformer in which the primary and secondary are physically separated and not connected by a conductor is called a(n) _____ transformer.
isolation
Shunt field windings are connected in parallel with the armature. They are wound with _____ turns of fairly _____ wire.
many small
The main power distribution system of a large industrial plant is generally shown using a(n) _____ diagram.
one line
For installations that will have both three-phase and single phase loads on a three-phase transformer, the utility company often provides a(n) _____ three-phase transformer.
open delta with one transformer center tapped
The ServoDisc motor is also often called a _____ motor
printed circuit
The speed of the disc servomotor can be varied by changing the amount of voltage supplied to the armature. The voltage is generally varied using _____.
pulse width
In a wye-connected system, the line voltage is higher than the phase voltage by a factor of _____.
square root of three
Another name for the three-phase wye connection is the _______________ connection.
star
If three-phase transformation is needed and a three-phase transformer of the proper size and turns ratio is not available, three single-phase transformers can be connected to form a _____.
three-phase bank
The pushing or turning force created by the magnetic field of the pole pieces and the magnetic field of the loop or armature is called _______________. Correct!
torque
An open delta connection is made using _____ single-phase transformers.
two
