Final for ac/dc machines
___ is the opposition to the flow of AC in a circuit due to inductance
Inductive reactance
____ is the lack of rotation when the stator field and the rotor field are parallel to one another
Locked in step
The motor _____ indicates whether a motor is rated to operate at either 50hz, 60hz, or both
Nameplate
Is a line through the armature cross section that is perpendicular to the maximum amount of magnetic flux
Neutral plane
A ____ relay is an overload relay that is used to protect a synchronous motor from damage from induced currents caused by the rotor falling out of step with the rotating stator field
Out of step (OSR)
Is any current over the normal current level
Overcurrent
When ____ are used, the rotors do not need to be excited
Permanent magnets
Is an extended flexible connection or braided copper conductor
Pigtail
Is a screw in fuse that uses metallic strip that melts when a predetermined amount of current flows through it
Plug fuse
The speed at which a plot phase motor runs is determined by the number of _____ in the motor and the frequency of the supply voltage
Poles
____ torque is the maximum torque required to accelerate a synchronous motor into synchronization at the rated voltage and frequency
Pull in
A wound rotor motor ____ is a device containing high wattage resistors that is designed to control the speed of a wound rotor motor and operate in variable speed mode for as long as needed
Regulator
In many cases a single phase motor is constructed with both a start and a ___ winding in the stator
Run
Increasing the resistance of the rotor while it is _____ reduces the current in the rotor windings and reduces the speed of the motor
Running
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
______ motor is a dc motor that has the field wiring connected in parallel with the armature
Shunt
A ____ ring is a metallic ring mounted on a motor shaft and electrically insulated from the shaft
Slip
___ control of a shaded pole motor is accomplished by adding windings in series with the main windings
Speed
The ____ is constructed of laminated iron sheets to minimize eddy current losses
Stator
____ torque is provided by the interaction of the stator field and the rotor field windings
Synchronous
Is a switch with tapped resistors used to switch a set of resistors in or out of a wound rotor circuit
Three pole rheostat
A rheostat uses a ___ to start the wound rotor motor
Three wire control circuit
The maximum_____ is produced when the maximum resistance is connected to the rotor and the induced frequency is at its highest
Torque
A dc motor can be made into a DC generator if an external prime mover is coupled to the motor shaft
True
A shaded pole motor is an AC motor that uses a shaded stator pole for starting
True
At approximately 95% of synchronous speed, dc excitation is applied to the wound rotor section
True
Brush material is typically composed of a mixture of carbon and graphite for high voltage machines and of graphite and metallics for low voltage machines
True
Is the synchronous motor is overloaded to the point where the rotor is pulled out of step with the rotating magnetic field, no torque is developed and the OSR takes the motor off line
True
Many older synchronous motors included a back up component for times when the discharge resistor failed
True
One of the most common circuit breaker designs combines magnetic element with a thermal element
True
Resistors used in a wound rotor motor are often referred to as secondary resistors, because the rotor is the secondary of the motor
True
Synchronous motors are similar to induction motors in that both have stator coils that produce a rotating magnetic field
True
The M1 connection I the outside slip ring, the M2 is the middle slip ring, and M3 connection is closed to the motor windings
True
The amortisseur winding of a synchronous motor is generally smaller than the squirrel cage winding of a comparable induction motor because the winding is only used for starting and is not expected to dissipate heat from continuous operation
True
The capacitors used to start motors are electrolytic capacitors
True
The current rating of the OCPD is determined by the size and type of conductors, control devices used, and loads connected to the curcuit
True
The end of a motor shaft is machined with a key way to contain a bar type key or with a circular slot that contains a half moon key
True
The main device in an overload relay is the eutectic allow tube
True
The main difference between different types of 3 phase motors is the design of the rotors and windings
True
The methods of applying a reduced voltage to a synchronous motor are the same as the methods of applying a reduced voltage to an induction motor
True
The purpose in making motors for two voyages 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 position on the commutator
True
The rotor of a single phase motor is the same as in an induction squirrel cage motor
True
The same rotating stator field that induced voltage in the amortisseur winding me also induces voltage in the field windings
True
There are no physical electrical connections between the stator and the rotor
True
To reverse the direction of most single phase motors all that is necessary is to switch the two start leads in the curcuit
True
Typical applications of capacitor motors include refrigerators, air conditioners, and some power tools
True
When no resistance is applied to the rotor circuit the starting torque is about 125% of the full load torque
True
When starting a synchronous motor the final step is to simultaneously remove the discharge resistor from the circuit and apply the dc voltage to the field windings on the rotor
True
Wound rotor stator windings are not short circuited they are wye connected with the free end of each winding connected to a slip ring
True
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
The __ rating is the maximum amount of voltage that can safely be applied to an overcurrent protection device and determines the ability of a fuse to suppress the internal arcing after fusible link melts
Voltage
Is the ability of a source to vary the output voltage in order to maintain system voltage as the load varies
Voltage regulation
The simplest method for a synchronous motor is ____ starting, where the motor is wired directly across the line conductors
Direct online (DOL)
A ___ resistor is a resistor used to discharge any ac potential that build up in the amortissuer winding of a rotor in a synchronous motor
Discharge
If the synchronous motor uses an AC generator mounted on the motor shaft, the generator starts providing ac power as soon as the rotor starts turning
False
In order to start automatically some single phase motors use a capacitor winding
False
Ina typical two speed split phase motor, one run winding and two start windings are used to develop two separate speeds
False
Ina 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
Most modern overcurrent protection devices are non current limiting devices
False
Once the motor starts the speed of the rotor decreases an the induced frequency increases, increasing the induction and induced current in the rotor
False
Overload relays are available in single, two, and three pole configurations
False
Resistance is increased as the motor accelerates in order to shift the point of maximum torque
False
Single phase 120v/240v power has four conductors with a potential of 240v between conductors A and B
False
Single phase are the most common 3 phase motor used in industry today
False
Starters never use a timer to automatically remove resistance from the rotor curcuit
False
Synchronous motors cannot be protected from damage caused by the loss of excitement
False
The exciter rotor output to the single phase bridge controls the level of excitation in the main DC field winding
False
The rotor of a wound rotor motor is constructed by placing solid conductor bars in the slots instead of the insulated coils of wire used in the squirrel cage induction motor
False
The shorting bars are mounted on a shaft that is used to transfer the power to the load
False
The stator of a wound rotor motor is different than the stator of a squirrel cage induction motor
False
Three styles of brushes are radial edge, trailing, and leader brushes
False
Three types of capacitor motors are the capacitor shut down motor, capacitor run, and capacitor start and run
False
Voltage is twisting force that is used to rotate a motor shaft
False
_____ current is the amount of current drawn when the motor is connected to the maximum load the motor is designed to drive
Full load
The basic component of a fuse is
Fusible link
Resistors designed for starting are able to dissipate the _____ generated during short time required for starting the motor
Heat
The stator ____ consist of coils of copper wire placed in slots 120 electrical degrees apart
Windings
____ motor is an induction motor with the squirrel cage conductor bars replaced with coils of wire and with added slip rings, brushes, and a resistor circuit
Wound rotor
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
0
Because of the high resistance and high slip design B motors are less efficient than other designs
False
Dc series motors are used where constant or adjustable speed is required and starting conditions are moderate
False
Eutectic alloys are installed in the combination starter, safety switch, or fuse panel
False
In a dual voltage wye connected three phase motor each phase coil is dived into two equal parts, by dividing the phase coil in two eleven terminal leads are available
False
Shaded pole motors are commonly _____ HP or less and have low starting torque
1/20
Synchronous motors that typically run faster than about ____ are considered high speed synchronous motors
450rpm
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
When the motor reaches approximately __% of full speed, the centrifugal switch opens, disconnecting the start winding from the circuit
75
A common type of relay used with synchronous motors is a
All of the above
A wound rotor motor can be distinguished from a squirrel cage induction motor by the presence of the
All of the above
Is a type of regulator
All of the above
The type of torque that is important to understand for synchronous motors is ___ torque
All of the above
____ windings or damper windings are squirrel cage conducting bars placed in slots on the pole faces and connected at the ends
Amortisseur
A___ exciter is an ac generator and rectifier mounted on a motor shaft
Brushless
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
Current flowing through the ____ in the rotor creates a magnetic field around the bars
Conducting bars
_____ overload relays are often used in heavy duty applications or special applications where normal time/ current curves of thermal overload relays do it provide satisfactory operation
Electromagnetic
The _____ typically is a shunt or compound wound DC generator with the armature in parallel with the shunt field and it's shunt field rheostat
Exciter generator
The ____ carries the entire rotor current
External resistor circuit
A capacitor run motor has the same starting torque as a capacitor start motor
False
A pigtail connects the slip ring to the power supply
False
A single phase motor does not have a method to create a rotating magnetic field
False
A synchronous motor has a three part rotor
False
A wound rotor motor is never started with full resistance in the circuit
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
An m-g set can be mounted at a remote location from the synchronous motor and cannot be used with more than one synchronous motor at a time
False
A typical dual voltage, 3 phase phase motor rating is
230/460. 240/480. 208-230/460v
A___ motor transfers energy from electric power to the load through the use of a rotating magnetic field
3-phase
Motor design______ is a design with normal starting torque and normals starting current
A
A ____ wound generator is a type of DC generator
All of the above
Circuit breakers can be designed to be operated
All of the above
The basic types of dc motors are dc series and ____
All of the above
_____ power is the product of the total current and voltage in a circuit
Apparent
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
In a ___ motor, one end of each of the three phase windings is internally connected to the other phase windings
Aye connected 3 phase
Is a motor component used to reduce friction and maintain clearance between the stationary parts and the moving shaft
Bearing
Common types of ____ include inverse time, adjustable trip, non adjustable trip, and instantaneous trip
Circuit breakers
A ____ motor is a motor where the current flows in the opposite direction on the series and shunt coils and the resulting net flux is the difference between the two fluxes
DC differential compounded
A ___ motor is a motor that uses magnets, not a coil of wire, for the field windings
DC permanent magnet
In a ____ motor each phase is wired end to end to form a completely closed circuit
Delta connected 3 phase
Motor design _____ has high starting torque and low starting current
Design A
____ motor is an electric motor that uses the principles of mutual induction to develop current and torque in the rotor
Induction
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
Is the rotating part of an ac motor
Rotor
Is an excessive current that leaves the normal current carrying path by going around the load and back to the power source
Short circuit
Locked rotor torque is also referred to as breakaway or starting torque
True
Motor circuits are the most common type of circuit that includes low level overloads
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 five major components of motor energy losses are resistance loss, core loss, bearing loss, windage loss, and sound loss
True
The magnetic fields around the individual conductors combine to create two separate magnetic fields aligned in opposite directions
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 characteristics and are available in a wide variety of torque characteristics
True
Three phase power is the standard power supplied by electrical power companies to almost all commercial and industrial locations
True
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_____ delay fuse is a dual element fuse that can detect and remove a short circuit almost instantly but allow small overloads to exist for a short period
Time
A DC shunt motor has lower starting torque than a DC series motor
True
A benefit of a dc generator is their ability to increase the voltage under changing load conditions
True
A continuous overload occurs when a motor is driving a load greater than the design load
True
A dc shiny motor can be run above its full voltage base speed by reducing current in the shunt fields
True
A rotor rotates at exactly the correct speed to induce the current required to develop the torque necessary to drive the load
True
A squirrel cage rotor is the most common design for induction motor rotor design
True
A typical overload occurs when the insulation between two wires is broken
False
In a ___ the series field windings and shunt windings are combined in a manner to take advantage of the characteristics of each
Compound wound generator
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
____ 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 a voltage induced in the windings that is opposite in polarity to that of the power supply
Countervoltage
Is a machine that uses dc connected to the files windings and armature to produce shaft rotation
Direct current motor
A dc generator always has a rotating field and a stationary armature
False
A ____ is the stationary part in a DC motor or generator
Field frame
In an induction motor, the ___ are in the stator and the rotors are designed to interact with the rotating stator magnetic fields
Field windings
Typical types of high voltage loads are fans, blowers, and punch presses
Flase
Is an unintentional connection between an ungrounded conductor and any grounded raceway, box, enclosure, or fitting
Ground fault
By design the plug fuse amperage rating is identified by the shape of the window on the fuse
True
Cartridge fuses are classified according to their performance, operation, and construction characteristics
True
Dc generators consist of field windings, and armature, a commutator and brushes
True
Dc motors perform better than AC motors in most traction equipment applications
True
Fuses and circuit breakers are used for ground fault and short circuit protection
True
In an induction motor, the shorted secondary in the rotor carries the induced secondary current
True
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
____ motors are designed to give the same maximum torque at all speeds
Constant torque
A dc motor can be reversed by changing the polarity of both the armature winding and the field winding
False
A heat overload measures the strength of the magnetic field around a wire instead of converting the current into heat
False
A melting alloy overload relay is an overload relay that uses the resistive heating to open a set of contacts
False
Because they overheat all dc permanent magnet motors are designed to run continuously
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
False
Each phase must have an unequal number of coils so the total number of coils must be divisible by 3
False
For single phase three sine curves placed 120 electrical degrees apart are used
False
The commutators are magnets or stationary windings used to produce the magnetic field in an alternator or motor
False
The direction of rotation of 3 phase motors cannot be reversed by interchanging any of the three phase power lines to the motor
False
The common types of torque related to motors are locked rotor torque
Full load Pull up Breakdown
A____ circuit breaker is a circuit breaker whose settings for the amperage trip set point or the time trip setpoint cannot be changed
Non adjustable trip
Is an excessive current that is confined to the normal current carrying conductors and is caused by a load that exceeds the full load torque rating of the motor
Overload
Is designed to carry harmless overloads but quickly remove the motor from the supply voltage when an overload has remained to long
Overload protection device
Induced secondary current interacts with the magnetic field and generates the ______ that turns the rotor and shaft
Torque
The combined magnetic field and the current flow interact to create the ____
Torque
In a delta connected three phase motor, the current starts to change as the sine wave rotated through the cycle and the amount of current flowing through each coil changes
True
In design A motors the locked rotor current is about 500% to 1000% of full load current
True
While almost all three phase motors have very similar stator designs, the main difference between different types of three phase motors is the design of the rotors and windings
True
The most common types of rotors are used in squirrel cage induction motors, _____ motors, and synchronous motors
Wound rotor