motors Final
control of shaded-pole motors is accomplished by adding windings in series with the main winding.
. Speed
Shaded-pole motors are commonly ___ HP or less and have low starting torque.
1/20
A capacitor-start motor operates much the same as a split-phase motor, in that it uses a centrifugal switch that opens at approximately ___% to ___% of full-load speed.
60; 80
_ power is the product of the total current and voltage in a circuit.
Apparent
A DC generator always has a rotating field and a stationary armature.
False
Single-phase, 120 V/240 V power has four conductors, with a potential of 240 V between conductors A and B.
False
The commutators are magnets or stationary windings used to produce the magnetic field in an alternator or motor.
False
Three styles of brushes are radial-edge, trailing, and leader brushes.
False
___ are auxiliary poles placed between the main field poles of the motor.
Interpoles
___ brushes are at an angle to the commutator and have less restricted up-and-down movement.
Leading-edge
A DC motor can be made into a DC generator if an external prime mover is coupled to the motor shaft.
True
A DC shunt motor can be run above its full-voltage base speed by reducing the current in the shunt fields.
True
A DC shunt motor has lower starting torque than a DC series motor.
True
A benefit of DC generators is their ability to increase the voltage under changing load conditions.
True
In Design A motors the locked-rotor current is about 500% to 1000% of full-load current.
True
Three-phase power is the standard power supplied by electrical power companies to almost all commercial and industrial locations.
True
Typical applications of capacitor motors include refrigerators, air conditioners, air compressors, and some power tools.
True
While almost all 3-phase motors have very similar stator designs, the main difference between different types of 3-phase motors is the design of the rotors and windings.
True
o reverse the direction of most single-phase motors, all that is necessary is to switch the two start leads in the circuit.
True
is the ability of a source to vary the output voltage in order to maintain system voltage as the load varies.
Voltage regulation
A(n) ___ is a voltage induced in the windings that is opposite in polarity to that of the power supply.
a. countervoltage
A typical dual-voltage, 3-phase motor rating is ___.
all of the above
The basic types of DC motors are DC series motors and ___ motors.
all of the above
The common types of torque related to motors are locked-rotor torque, and ___ torque
all of the above
As the rotor begins to move, the frequency of the induced current in the rotor decreases, until the rotor approaches synchronous speed, where the rotor frequency approaches ___ Hz.
b. 0
Motor Design ___ has high starting torque and low starting current.
b. C
A ___ motor is a motor that uses magnets, not a coil of wire, for the field windings.
b. DC permanent-magnet
A ___ is a motor component used to reduce friction and maintain clearance between the stationary parts and the moving shaft.
bearing
A ___ motor has one capacitor in series with the start winding and one capacitor in series with the run winding
c. capacitor start-and-run
A ___ is the rotating part of an AC motor.
c. roto
In an induction motor, the ___ are in the stator and the rotors are designed to interact with the rotating stator magnetic field.
field windings
The motor ___ indicates whether a motor is rated to operate at either 50 Hz, 60 Hz, or both.
nameplate
Induced secondary current interacts with the magnetic field and generates the ___ that turns the rotor and shaft.
torque
The end of a motor shaft is machined with a keyway to contain a bar-type key or with a circular slot that contains a half-moon key.
True
Current flowing through the ___ in the rotor creates a magnetic field around the bars.
conducting bars
___ is the process where the armature current is periodically reversed in order to keep the motor torque in the same direction during the entire armature rotation.
Commutation
Single-phase are the most common 3-phase motors used in industry today.
False
The direction of rotation of 3-phase motors cannot be reversed by interchanging any of the 3-phase power lines to the motor.
False
Three types of capacitor motors are the capacitor shut-down motor, capacitor-run motor, and the capacitor start-and-run motor.
False
Typical types of high-voltage loads are fans, blowers, and punch presses.
False
A rotor always rotates at exactly the correct speed to induce the current required to develop the torque necessary to drive the load.
True
Locked-rotor torque is also referred to as breakaway or starting torque.
True
The speed at which a split-phase motor runs is determined by the number of ___ in the motor and the frequency of the supply voltage.
poles
For a shaded-pole motor, the stator has two or more ___ poles that are divided into parts.
salient
The function of the ___ is to delay the magnetic flux in the area of the pole that is shaded.
shaded pole
A(n) ___ motor is a DC motor that has the field wiring connected in parallel with the armature.
shunt
A ___ is the fixed, unmoving part of a motor, consisting of a core and windings, that converts electrical energy to the energy of a magnetic field.
stator
The ___ is the stationary part of an AC motor.
stator
A shorting ring, or ___ ring, is a metal ring used to electrically connect the bars of a squirrel-cage rotor at the end of the cage frame.
. conducting
A(n) ___ is a machine that uses DC connected to the field windings and armature to produce shaft rotation.
. direct-current motor
The ___ is a line through the armature cross section that is perpendicular to the maximum amount of magnetic flux.
. neutral plane
In many cases, a single-phase motor is constructed with both a start and a ___ winding in the stator.
. run
A ___ motor is commonly wound to run on either six or eight poles
. two-speed, split-phase
A single-___ motor is a motor that operates at only one voltage level.
. voltage
A ___ motor is a motor where the current flows in the opposite direction in the series and shunt coils and the resulting net flux is the difference between the two fluxes.
DC differential-compounded
A DC motor can be reversed by changing the polarity of both the armature winding and the field winding.
False
A capacitor-run motor has the same starting torque as a capacitor-start motor.
False
A single-phase motor does not have a method to create a rotating magnetic field.
False
Although a capacitor-start motor develops less starting torque than a split-phase motor, both motor types are the same when running because the capacitor and start windings are removed from the circuit when the motor comes up to speed.
False
Because of the high resistance and high slip, Design B motors are less efficient than other designs.
False
In a typical two-speed, split-phase motor, one run winding and two start windings are used to develop two separate speeds.
False
In a wye-connected, 3-phase motor, the north or south polarity of the poles is determined by the direction of the voltage rating and the motor design.
False
In order to start automatically, some single-phase motors use a capacitor winding.
False
A shaded-pole motor is an AC motor that uses a shaded stator pole for starting.
True
A squirrel-cage rotor is the most common design for induction-motor rotor design.
True
DC generators consist of field windings, an armature, a commutator, and brushes.
True
DC motors perform better than AC motors in most traction equipment applications.
True
In a delta-connected, 3-phase motor, the current starts to change as the sine wave rotates through the cycle and the amount of current flowing through each coil changes.
True
In an induction motor, the shorted secondary in the rotor carries the induced secondary current.
True
Since each DC source has one positive and one negative terminal, there must be at least two brushes and two brush holders.
True
The capacitors used to start motors are electrolytic capacitors.
True
The five major components of motor energy losses are resistance loss, core loss, bearing loss, windage loss, and sound loss. These losses add up to the total loss of a motor.
True
The purpose in making motors for two voltages is to enable the same motor to be used with two different power line voltages.
True
The purpose of the compensating windings is to help interpoles maintain neutral position on the commutator.
True
The rotor of a single-phase motor is the same as in an induction squirrel-cage motor.
True
The torque-speed characteristic of a motor must match the load the motor is to drive.
True
Three-phase motors have a fairly constant speed characteristic and are available in a wide variety of torque characteristics.
True
A ___-wound generator is a type of DC generator.
d. all of the above
In a ___, the series field windings and shunt field windings are combined in a manner to take advantage of the characteristics of each.
d. compound-wound generator
A ___ is the stationary part in a DC motor or generator.
d. field frame
The most common types of rotors are used in squirrel-cage induction motors, ___ motors, and synchronous motors.
wound-rotor
In a ___ motor, one end of each of the three phase windings is internally connected to the other phase windings.
wye-connected, 3-phase
In a ___ motor, each phase is wired end-to-end to form a completely closed circuit.
delta-connected, 3-phase
A(n) ___ motor is an electric motor that uses the principles of mutual induction to develop current and torque in the rotor.
induction
A ___ motor transfers energy from electric power to the load through the use of a rotating magnetic field.
. 3-phase
When the motor reaches approximately ___% of full speed, the centrifugal switch opens, disconnecting the start winding from the circuit.
. 75
Motor Design ___ is a design with normal starting torque and normal starting curren
. A
motors are designed to give the same maximum torque at all speeds.
. Constant-torque
___ loss is the total energy loss in the stator and rotor cores due to circulating currents and to the magnetic field escaping from the core.
. Core
_ is the opposition to the flow of AC in a circuit due to inductance.
. Inductive reactance
__ is the lack of rotation when the stator's field and the rotor's field are parallel to one another.
. Locked in step
A(n) ___ is the rotating part of a DC motor, consisting of the laminated core with slots for the coils, the main shaft, and the commutator and brushes.
. armature
A ___ motor is a single-phase motor with a capacitor connected in series with the start windings to produce phase displacement in the start winding.
. capacitor
Because they cannot overheat, all DC permanent-magnet motors are designed to run continuously.
False
DC series motors are used where constant or adjustable speed is required and starting conditions are moderate
False
DC series motors can develop only about 125% of full-load torque upon starting.
False
Design A motors are suitable for equipment with high-inertia starts, such as positive-displacement pumps and heavily loaded conveyors.
False
Each phase must have an unequal number of coils, so the total number of coils must be divisible by the number 3.
False
For single-phase, three sine curves placed 120 electrical degrees apart are used.
False
In a dual-voltage, wye-connected, 3-phase motor, each phase coil (A, B, and C) is divided into two equal parts; by dividing the phase coils in two, eleven terminal leads are available.
False