Power can be expressed in foot-pounds per second, but is often
expressed in horsepower (HP). This unit was defined in the
18th century by James Watt. Watt sold steam engines and was
asked how many horses one steam engine would replace. He
had horses walk around a wheel that would lift a weight. He
found that each horse would average about 550 foot-pounds of
work per second. One horsepower is equivalent to 500 footpounds
per second or 33,000 foot-pounds per minute.
The following formula can be used to calculate horsepower
when torque (lb-ft) and speed (RPM) are known. It can be seen
from the formula that an increase of torque, speed, or both will
cause a corresponding increase in horsepower.
HP = T * RPM / 5250
Saturday, December 13, 2008
Power
Power is the rate of doing work, or work divided by time.
In other words, power is the amount of work it takes to move
the package from one point to another point, divided by the
time.
power = force*distance / time
power = work / time
In other words, power is the amount of work it takes to move
the package from one point to another point, divided by the
time.
power = force*distance / time
power = work / time
Work
Whenever a force of any kind causes motion, work is
accomplished. For example, work is accomplished when an
object on a conveyor is moved from one point to another.
Work is defined by the product of the net force (F) applied and
the distance (d) moved. If twice the force is applied, twice the
work is done. If an object moves twice the distance, twice the
work is done.
W = F x d
accomplished. For example, work is accomplished when an
object on a conveyor is moved from one point to another.
Work is defined by the product of the net force (F) applied and
the distance (d) moved. If twice the force is applied, twice the
work is done. If an object moves twice the distance, twice the
work is done.
W = F x d
Friction
A large amount of force is applied to overcome the inertia of
the system at rest to start it moving. Because friction removes
energy from a mechanical system, a continual force must
be applied to keep an object in motion. The law of inertia is
still valid, however, since the force applied is needed only to
compensate for the energy lost.
Once the system is in motion, only the energy required to
compensate for various losses need be applied to keep it in
motion. In the previous illustration, for example: these losses
include:
• Friction within motor and driven equipment bearings
• Windage losses in the motor and driven equipment
• Friction between material on winder and rollers
the system at rest to start it moving. Because friction removes
energy from a mechanical system, a continual force must
be applied to keep an object in motion. The law of inertia is
still valid, however, since the force applied is needed only to
compensate for the energy lost.
Once the system is in motion, only the energy required to
compensate for various losses need be applied to keep it in
motion. In the previous illustration, for example: these losses
include:
• Friction within motor and driven equipment bearings
• Windage losses in the motor and driven equipment
• Friction between material on winder and rollers
Law of Inertia
Mechanical systems are subject to the law of inertia. The law
of inertia states that an object will tend to remain in its current
state of rest or motion unless acted upon by an external force.
This property of resistance to acceleration/deceleration is
referred to as the moment of inertia. The English system of
measurement is pound-feet squared (lb-ft2).
If we look at a continuous roll of paper, as it unwinds, we know
that when the roll is stopped, it would take a certain amount
of force to overcome the inertia of the roll to get it rolling. The
force required to overcome this inertia can come from a source
of energy such as a motor. Once rolling, the paper will continue
unwinding until another force acts on it to bring it to a stop.
of inertia states that an object will tend to remain in its current
state of rest or motion unless acted upon by an external force.
This property of resistance to acceleration/deceleration is
referred to as the moment of inertia. The English system of
measurement is pound-feet squared (lb-ft2).
If we look at a continuous roll of paper, as it unwinds, we know
that when the roll is stopped, it would take a certain amount
of force to overcome the inertia of the roll to get it rolling. The
force required to overcome this inertia can come from a source
of energy such as a motor. Once rolling, the paper will continue
unwinding until another force acts on it to bring it to a stop.
Acceleration
An object can change speed. An increase in speed is called
acceleration. Acceleration occurs only when there is a change
in the force acting upon the object. An object can also change
from a higher to a lower speed. This is known as deceleration
(negative acceleration). A rotating object, for example, can
accelerate from 10 RPM to 20 RPM, or decelerate from 20
RPM to 10 RPM.
acceleration. Acceleration occurs only when there is a change
in the force acting upon the object. An object can also change
from a higher to a lower speed. This is known as deceleration
(negative acceleration). A rotating object, for example, can
accelerate from 10 RPM to 20 RPM, or decelerate from 20
RPM to 10 RPM.
Angular (Rotational) Speed
The angular speed of a rotating object is a measurement of how
long it takes a given point on the object to make one complete
revolution from its starting point. Angular speed is generally
given in revolutions per minute (RPM). An object that makes ten
complete revolutions in one minute, for example, has a speed
of 10 RPM.
long it takes a given point on the object to make one complete
revolution from its starting point. Angular speed is generally
given in revolutions per minute (RPM). An object that makes ten
complete revolutions in one minute, for example, has a speed
of 10 RPM.
Linear Speed
The linear speed of an object is a measure of how long it takes
the object to get from point A to point B. Linear speed is usually
given in a form such as meters per second (m/s). For example, if
the distance between point A and point B were 10 meters, and
it took 2 seconds to travel the distance, the speed would be 5 m/s.
the object to get from point A to point B. Linear speed is usually
given in a form such as meters per second (m/s). For example, if
the distance between point A and point B were 10 meters, and
it took 2 seconds to travel the distance, the speed would be 5 m/s.
Speed
An object in motion travels a given distance in a given time.
Speed is the ratio of the distance traveled to the time it takes to
travel the distance.
Speed = Distance/time
Speed is the ratio of the distance traveled to the time it takes to
travel the distance.
Speed = Distance/time
Torque
Torque is a twisting or turning force that tends to cause an
object to rotate. A force applied to the end of a lever, for
example, causes a turning effect or torque at the pivot point.
Torque (τ) is the product of force and radius (lever distance).
Torque (τ) = Force x Radius
In the English system torque is measured in pound-feet (lb-ft) or
pound-inches (lb-in). If 10 lbs of force were applied to a lever 1
foot long, for example, there would be 10 lb-ft of torque.
An increase in force or radius would result in a corresponding
increase in torque. Increasing the radius to 2 feet, for example,
results in 20 lb-ft of torque.
object to rotate. A force applied to the end of a lever, for
example, causes a turning effect or torque at the pivot point.
Torque (τ) is the product of force and radius (lever distance).
Torque (τ) = Force x Radius
In the English system torque is measured in pound-feet (lb-ft) or
pound-inches (lb-in). If 10 lbs of force were applied to a lever 1
foot long, for example, there would be 10 lb-ft of torque.
An increase in force or radius would result in a corresponding
increase in torque. Increasing the radius to 2 feet, for example,
results in 20 lb-ft of torque.
Net Force
Net force is the vector sum of all forces that act on an object,
including friction and gravity. When forces are applied in the
same direction they are added. For example, if two 10 lb forces
were applied in the same direction the net force would be 20 lb.
If 10 lb of force were applied in one direction and 5 lb of force
applied in the opposite direction, the net force would be 5 lb
and the object would move in the direction of the greater force
including friction and gravity. When forces are applied in the
same direction they are added. For example, if two 10 lb forces
were applied in the same direction the net force would be 20 lb.
If 10 lb of force were applied in one direction and 5 lb of force
applied in the opposite direction, the net force would be 5 lb
and the object would move in the direction of the greater force
Force
In simple terms, a force is a push or a pull. Force may be
caused by electromagnetism, gravity, or a combination of
physical means.
caused by electromagnetism, gravity, or a combination of
physical means.
Variable Speed Drives
The speed of a motor can be controlled by using some type of
electronic drive equipment, referred to as variable or adjustable
speed drives. Variable speed drives used to control DC motors
are called DC drives. Variable speed drives used to control AC
motors are called AC drives. The term inverter is also used to
describe an AC variable speed drive. The inverter is only one
part of an AC drive, however, it is common practice to refer to
an AC drive as an inverter.
Before discussing AC drives it is necessary to understand some
of the basic terminology associated with drive operation. Many
of these terms are familiar to us in some other context. Later in
the course we will see how these terms apply to AC drives.
electronic drive equipment, referred to as variable or adjustable
speed drives. Variable speed drives used to control DC motors
are called DC drives. Variable speed drives used to control AC
motors are called AC drives. The term inverter is also used to
describe an AC variable speed drive. The inverter is only one
part of an AC drive, however, it is common practice to refer to
an AC drive as an inverter.
Before discussing AC drives it is necessary to understand some
of the basic terminology associated with drive operation. Many
of these terms are familiar to us in some other context. Later in
the course we will see how these terms apply to AC drives.
Mechanical Basics
In many commercial, industrial, and utility applications electric
motors are used to transform electrical energy into mechanical
energy. Those electric motors may be part of a pump or fan,
or they may be connected to some other form of mechanical
equipment such as a conveyor or mixer. In many of these
applications the speed of the system is determined primarily by
its mechanical design and loading. For an increasing number of
these applications, however, it is necessary to control the speed
of the system by controlling the speed of the motor.
motors are used to transform electrical energy into mechanical
energy. Those electric motors may be part of a pump or fan,
or they may be connected to some other form of mechanical
equipment such as a conveyor or mixer. In many of these
applications the speed of the system is determined primarily by
its mechanical design and loading. For an increasing number of
these applications, however, it is necessary to control the speed
of the system by controlling the speed of the motor.
AC Drives and Totally Integrated
This course focuses on several drives which
include the MICROMASTER and MASTERDRIVE VC, which are
important elements of the TIA strategy.
Totally Integrated Automation (TIA) is more than a concept. TIA
Automation is a strategy that emphasizes the
seamless integration of automation products. The TIA strategy
incorporates a wide variety of automation products such
as programmable controllers, computer numerical controls,
Human Machine Interfaces (HMI), and drives which are easily
connected via open protocol networks.
include the MICROMASTER and MASTERDRIVE VC, which are
important elements of the TIA strategy.
Totally Integrated Automation (TIA) is more than a concept. TIA
Automation is a strategy that emphasizes the
seamless integration of automation products. The TIA strategy
incorporates a wide variety of automation products such
as programmable controllers, computer numerical controls,
Human Machine Interfaces (HMI), and drives which are easily
connected via open protocol networks.
Introduction
This course covers Basics of AC Drives and related products.
Upon completion of Basics of AC Drives you should be able to:
• Explain the concept of force, inertia, speed, and torque
• Explain the difference between work and power
• Describe the construction of a squirrel cage AC motor
• Identify the nameplate information of an AC motor
necessary for application to an AC Drive
• Describe the operation of a three-phase rotating magnetic
field
• Calculate synchronous speed, slip, and rotor speed
• Describe the relationship between V/Hz, torque, and
current
• Describe the basic construction and operation of a PWM
type AC drive
• Describe features and operation of the Siemens
MICROMASTER and MASTERDRIVE VC
• Describe the characteristics of constant torque, constant
horsepower, and variable torque applications
This knowledge will help you better understand customer
applications. In addition, you will be able to describe products
to customers and determine important differences between
products. You should complete Basics of Electricity before
attempting Basics of AC Drives. An understanding of many of
the concepts covered in Basics of Electricity is required for
Basics of AC Drives.
Upon completion of Basics of AC Drives you should be able to:
• Explain the concept of force, inertia, speed, and torque
• Explain the difference between work and power
• Describe the construction of a squirrel cage AC motor
• Identify the nameplate information of an AC motor
necessary for application to an AC Drive
• Describe the operation of a three-phase rotating magnetic
field
• Calculate synchronous speed, slip, and rotor speed
• Describe the relationship between V/Hz, torque, and
current
• Describe the basic construction and operation of a PWM
type AC drive
• Describe features and operation of the Siemens
MICROMASTER and MASTERDRIVE VC
• Describe the characteristics of constant torque, constant
horsepower, and variable torque applications
This knowledge will help you better understand customer
applications. In addition, you will be able to describe products
to customers and determine important differences between
products. You should complete Basics of Electricity before
attempting Basics of AC Drives. An understanding of many of
the concepts covered in Basics of Electricity is required for
Basics of AC Drives.
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