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ELECT 218 AC/DC Motors midterm

Terms in this set (84)

The methods used to determine motor torque are _________________, current measurements, and dynamometer.
prony brake
An application for measuring motor torque is to determine if the motor is ____________________.
overloaded
A dynamometer is basically a DC _________________________.
generator
As motor torque increases on an electric motor, ___________________ also increases.
current
A ___________________ is directly coupled to a motor shaft and held by a spring scale.
Dynamometer
Operating a motor in an overload condition results in a shortened _________________________.
service life for the motor
The rotational speed of a motor is measured in ______________.
Revolutions per minute (RPM)
The device that is most often used to measure motor speed is the _______________________.
Tachometer
A ____________________ tachometer determines motor shaft speed by counting the number of times a reflective tape on the motor shaft passes through its light.
photo
One of the applications of measuring motor speed is to check for positive ______________________ condition of an AC motor.
motor overload
A tachometer __________________(can/cannot) be used to check the performance of speed control.
can
__________________ is a measure of the turning effort caused by a force acting on a part that rotates.
torque
The S.I. units of torque are
Newton Meters (N-M)
Torque is increased by either applying the force further from the ______________ or by increasing the force applied.
pivot point
The ___________________ on an electric motor is the amount of torque that the motor must generate at its shaft to overcome the resistance caused by the device that is driven.
torque load
To turn a load, the electric motor must generate a torque that __________ the torque requirements of the load.
exceeds
on a drive belt system, the torque that is delivered to the load depends on the _________________ratio.
pulley
The effect that was the gear or pulley ratio has on speed is exactly ______________to the effect on torque.
opposite
Torque is developed in an electric motor because of the interaction of different __________________.
magnetic fields
A DC shunt motor has its field windings connected in ___________________ with the armature.
parallel
An advantage of the self-excited DC shunt motor is that it is able to ___________ its speed over a wide load range.
Operate/ control
A DC shunt motor _________(does/does not) provide high starting torque.
Does not
A DC shunt motor will not ________ if there is no load connected to it, unlike a DC series motor.
Run away
Major components for all motors:
Stator, rotor/armature, shaft. DC motors: commutator, brushes
When the shunt field is connected to the same power supply as the armature, it is called a _______ shunt field
Self-excited
The ________ windings have much less resistance than the field windings.
Armature
When a separate power supply is used for a shunt field, it is called a _______ shunt field.
Separately- excited
One of the major advantages of a separately- excited shunt motor is that the motor can be operated________ its rated name-plate speed.
Beyond
When a DC motor is connected in a separately- excited configuration, as the field current is decreased, the motor speed_________ (increases/decreases)
Increases
The direction of rotation on a DC shunt motor can be reversed by either reversing the field connections or the ________ connections
Armature
The process of reducing the field current of a separately- excited shunt motor is called________
Field weakening
The maximum speed of a self-excited shunt motor is determined by the_______
Armature current
A DC _______ motor is a motor with a field connected in both series and in shunt with the armature.
Compound
A DC compound motor provides _______ (higher/lower) starting torque than a shunt motor.
Higher
A DC compound motor provides better _______ control than a series motor.
Speed
If the series and shunt windings are connected in a compound motor so that their magnetic fields have the same polarity, the motor is configured as a ________ compound motor.
Cumulative
The _______ compound motor has very few applications and its avoided for the most part
Differential
The only sure method to reverse the direction of rotation on a cumulative compound motor is to reverse the ________ connections.
Armature
Electric motors rely on the principle of _______ to convert electrical power into mechanical power.
Inductance
The three categories of electric motors are DC, AC and _______ motors
Universal
There are ______ rules of safe dress around motors.
5
Always _____ a motor from electrical power before installing, coupling, or servicing it.
Disconnect
A motor must be properly ________ to the load it is driving.
Coupled
Dirt buildup can cause excessive________ which can reduce the life of a motor.
Heating
_________ clothing should always be worn when working around a motor.
Tight fighting
Get someone to help move a motor or mount an electric motor if it is too _______ to handle alone.
Heavy
An electric motor must be kept ______ and dry.
Clean
make sure that no _____ parts or tools are left around a motor when it is in operation.
Loose
Installing the wrong motor can cause _______ to the motor and the load its coupled to.
Damage
The ________ are the stator of the DC motor.
field windings
The primary purpose of the __________ are to reduce sparking between the brushes and the commutator.
Interpoles
The rotation of an electric motor is created by the interaction of two different ___________.
Magnetic fields
The 3 basic motor configurations are: _________ , shunt and compound.
Series
A DC series motor has the field windings connected in _________ with the armature.
Series
________ is a rotary force produced by a motor.
Torque
The major advantage of a DC series motor when it is operated, a condition known as ___________ will occur.
Run away
The easy access to ______ often leads to the selection of an electric motor for application.
Electricity
Since a motor has moving parts, it must be ______ on a regular schedule in order to ensure longer life and proper operation.
Serviced
The _______ is the stationary part of an electric motor.
Stator
The rotor is the _______ part of an electric motor
Rotating
One application of a DC series motor is a ________ , which requires high starting torque to lift items.
Crane
To reverse the direction of rotation on a DC motor, either reverse the ________ connections or the armature connections, but not both.
Field windings
Reversing the ______ leads to a DC motor will not affect the direction of rotation.
Power supply
The standard direction of rotation for all Amatrol- supplied motors is _________.
Counter-clockwise
The shaft rotation direction can be determined by observing the motor from the end _______ the shaft.
Opposite
Using both methods to reverse the direction of rotation of a DC motor at the same time ________ (will/will not) change the direction of the rotation.
Will not
The ________ method will not work with all DC motor configurations.
Field windings
___________ is the rate of doing work.
Motor Power
The U.S. Customary power unit for motors is _________
horse power (Hp)
The S.I. power unit for motors is __________
kilowatts (KW)
Efficiency of a motor is the ratio of the _______ power to the input
output
On a DC motor, the current used to calculate the input power is the ________ current.
Input
A motor converts ___________ power into mechanical power.
electrical
The __________ of a motor are a deciding factor in the selection of the proper motor for an application.
performance characteristics
Four characteristics of a motor that are used for selection are speed, ________ , power output, and efficiency.
Torque output
Many motor characteristics can be determined using the __________ for a motor.
Specification sheet
Motor power is given in kilowatts in the S.I. system and _____ the U.S. customary system.
horse power (Hp)
Efficiency is the ratio of motor _________ to electrical input motor.
output power
Motor efficiency is given as a(n) ___________
percentage
The _______ torque is the initial torque necessary to accelerate a load to full speed.
starting
_________ and torque are the two performance characteristics of a motor that are most often used to select a motor for an application.
Speed regulation
A ______ configured DC motor usually provides the highest starting torque.
Series
Speed ______ refers to the motor's ability to maintain speed as the load increases.
regulation
A _______ configured DC motor usually provides the best speed regulation.
Shunt
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