Basics of DC Drives

Basics of DC Drives
Table of Contents
Introduction...............................................................................2
Totally Integrated Automation and DC Drives...........................4
Mechanical Basics.....................................................................6
DC Motors............................................................................... 12
Basic DC Motor Operation....................................................... 15
Types of DC Motors.................................................................20
DC Motor Ratings....................................................................23
Speed/Torque Relationships of Shunt Connected Motors.......27
Basic DC Drives.......................................................................31
Converting AC to DC...............................................................34
Basic Drive Operation..............................................................38
SIMOREG 6RA70 DC MASTER Electronics............................48
Parameters and Function Blocks.............................................63
Applications.............................................................................70
Application Examples.............................................................. 71
Selecting a Siemens DC Drive................................................. 74
Review Answers......................................................................78
Final Exam...............................................................................79
quickSTEP Online Courses......................................................84
Introduction
Welcome to another course in the STEP series,
Siemens Technical Education Program, designed to prepare
our distributors to sell Siemens Energy & Automation products
more effectively. This course covers Basics of DC Drives and
related products.
Upon completion of Basics of DC Drives you will be able to:
Explain the concepts of force, inertia, speed, and torque
•
Explain the difference between work and power
•
Describe the operation of a DC motor
•
Identify types of DC motors by their windings
•
Identify nameplate information on a DC motor necessary
for application to a DC drive
•
Identify the differences between a power module and a
base drive
•
Explain the process of converting AC to DC using
thyristors
•
Describe the basic construction of a DC drive
•
Explain the significant differences between 1- and 4quadrant operation in a DC drive
•
Describe features and operation of the Siemens 6RA70
DC MASTER
•
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 better able to describe
products to customers and determine important differences
between products.
If you are an employee of a Siemens Energy & Automation
authorized distributor, fill out the final exam tear-out card and
mail in the card. We will mail you a certificate of completion if
you score a passing grade. Good luck with your efforts.
SIMOREG, SIMOREG DC-MASTER, SIMOVIS, and SIMOLINK
are registered trademarks of Siemens Energy & Automation,
Inc.
Other trademarks are the property of their respective owners.
Totally Integrated Automation
and DC Drives
Totally Integrated Automation
Totally Integrated Automation (TIA) is a strategy developed
by Siemens 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 DC drives which are easily connected
via open protocol networks. An important aspect of TIA is the
ability of devices to communicate with each other over various
network protocols such as PROFIBUS-DP.
Siemens DC Drives
SIMOREG® is the trade name for Siemens adjustable speed
DC Drives. SIMOREG stands for SIemens MOtor REGulator.
Siemens DC drives are an important element of the TIA
strategy. DC motors were the first practical device to convert
electrical energy into mechanical energy. DC motors, coupled
with DC drives such as the Siemens SIMOREG 6RA70, have
been widely used in industrial drive applications for years,
offering very precise control.
Although AC motors and vector-control drives now offer
alternatives to DC, there are many applications where DC
drives offer advantages in operator friendliness, reliability, cost
effectiveness, and performance. We will discuss applications
later in the course.
Mechanical Basics
Before discussing Siemens DC drives it is necessary to
understand some of the basic terminology associated with
the mechanics of DC 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 DC drives.
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. The English unit of measurement for force is
pounds (lb).
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.
If 10 lb of force were applied equally in both directions, the net
force would be zero and the object would not move.
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 () is the product of force and radius (lever distance). Torque () = 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.
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.
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 feet per second (f/s). For example, if the
distance between point A and point B were 10 feet, and it took
2 seconds to travel the distance, the speed would be 5 f/s.
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.
Acceleration
An object can change speed. An increase in speed is called
acceleration. Acceleration occurs 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.
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
2
measurement is pound-feet squared (lb-ft ).
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.
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:
•
•
•
Work
Friction within motor and driven equipment bearings
Windage losses in the motor and driven equipment
Friction between material on winder and rollers
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=Fxd
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.
Horsepower 10
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.
Power in an electrical circuit is measured in watts (W) or
kilowatts (kW). Variable speed drives and motors manufactured
in the United States are generally rated in horsepower (HP);
however, it is becoming common practice to rate equipment
using the International System of Units (SI units) of watts and
kilowatts.
Review 1
1.
____________ is the trade name for Siemens motor
generators (DC drives).
2. If 20 lb of force where applied in one direction and 5 lb
of force applied in the opposite direction, the net force
would be ____________ lb.
3. If 5 lb of force were applied to a radius of 3 feet, the
torque would be ____________ lb-ft.
4. Speed is determined by ___________ .
a.dividing Time by Distance
b.dividing Distance by Time
c.multiplying Distance x Time
d.subtracting Distance from Time
5. Work is accomplished whenever ____________ causes
motion.
6. 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 ____________ ____________ .
11
DC Motors
DC motors have been used in industrial applications for years.
Coupled with a DC drive, DC motors provide very precise
control. DC motors can be used with conveyors, elevators,
extruders, marine applications, material handling, paper,
plastics, rubber, steel, and textile applications to name a few.
Construction
DC motors are made up of several major components which
include the following:
•Frame
•Shaft
•Bearings
•Main Field Windings (Stator)
•Armature (Rotor)
•Commutator
•Brush Assembly
12
Of these components, it is important to understand the
electrical characteristics of the main field windings, known as
the stator, and the rotating windings, known as the armature.
An understanding of these two components will help with the
understanding of various functions of a DC Drive.
Basic Construction
The relationship of the electrical components of a DC motor is
shown in the following illustration. Field windings are mounted
on pole pieces to form electromagnets. In smaller DC motors
the field may be a permanent magnet. However, in larger DC
fields the field is typically an electromagnet. Field windings and
pole pieces are bolted to the frame. The armature is inserted
between the field windings. The armature is supported by
bearings and end brackets (not shown). Carbon brushes are
held against the commutator.
13
Armature
The armature rotates between the poles of the field windings.
The armature is made up of a shaft, core, armature windings,
and a commutator. The armature windings are usually form
wound and then placed in slots in the core.
Brushes
Brushes ride on the side of the commutator to provide supply
voltage to the motor. The DC motor is mechanically complex
which can cause problems for them in certain adverse
environments. Dirt on the commutator, for example, can inhibit
supply voltage from reaching the armature. A certain amount
of care is required when using DC motors in certain industrial
applications. Corrosives can damage the commutator. In
addition, the action of the carbon brush against the commutator
causes sparks which may be problematic in hazardous
environments.
14
Basic DC Motor Operation
Magnetic Fields
You will recall from the previous section that there are two
electrical elements of a DC motor, the field windings and
the armature. The armature windings are made up of current
carrying conductors that terminate at a commutator. DC voltage
is applied to the armature windings through carbon brushes
which ride on the commutator.
In small DC motors, permanent magnets can be used
for the stator. However, in large motors used in industrial
applications the stator is an electromagnet. When voltage is
applied to stator windings an electromagnet with north and
south poles is established. The resultant magnetic field is
static (non-rotational). For simplicity of explanation, the stator
will be represented by permanent magnets in the following
illustrations.
15
Magnetic Fields
A DC motor rotates as a result of two magnetic fields
interacting with each other. The first field is the main field
that exists in the stator windings. The second field exists in
the armature. Whenever current flows through a conductor a
magnetic field is generated around the conductor.
Right-Hand Rule for Motors
A relationship, known as the right-hand rule for motors, exists
between the main field, the field around a conductor, and the
direction the conductor tends to move.
If the thumb, index finger, and third finger are held at right
angles to each other and placed as shown in the following
illustration so that the index finger points in the direction of
the main field flux and the third finger points in the direction of
electron flow in the conductor, the thumb will indicate direction
of conductor motion. As can be seen from the following
illustration, conductors on the left side tend to be pushed up.
Conductors on the right side tend to be pushed down. This
results in a motor that is rotating in a clockwise direction. You
will see later that the amount of force acting on the conductor
to produce rotation is directly proportional to the field strength
and the amount of current flowing in the conductor.
16
CEMF
Whenever a conductor cuts through lines of flux a voltage
is induced in the conductor. In a DC motor the armature
conductors cut through the lines of flux of the main field. The
voltage induced into the armature conductors is always in
opposition to the applied DC voltage. Since the voltage induced
into the conductor is in opposition to the applied voltage it is
known as CEMF (counter electromotive force). CEMF reduces
the applied armature voltage.
The amount of induced CEMF depends on many factors such
as the number of turns in the coils, flux density, and the speed
which the flux lines are cut.
Armature Field
An armature, as we have learned, is made up of many coils and
conductors. The magnetic fields of these conductors combine
to form a resultant armature field with a north and south pole.
The north pole of the armature is attracted to the south pole
of the main field. The south pole of the armature is attracted
to the north pole of the main field. This attraction exerts a
continuous torque on the armature. Even though the armature
is continuously moving, the resultant field appears to be fixed.
This is due to commutation, which will be discussed next.
17
Commutation
In the following illustration of a DC motor only one armature
conductor is shown. Half of the conductor has been shaded
black, the other half white. The conductor is connected to two
segments of the commutator.
In position 1 the black half of the conductor is in contact with
the negative side of the DC applied voltage. Current flows away
from the commutator on the black half of the conductor and
returns to the positive side, flowing towards the commutator on
the white half.
In position 2 the conductor has rotated 90°. At this position
the conductor is lined up with the main field. This conductor is
no longer cutting main field magnetic lines of flux; therefore,
no voltage is being induced into the conductor. Only applied
voltage is present. The conductor coil is short-circuited by the
brush spanning the two adjacent commutator segments. This
allows current to reverse as the black commutator segment
makes contact with the positive side of the applied DC voltage
and the white commutator segment makes contact with the
negative side of the applied DC voltage.
18
As the conductor continues to rotate from position 2 to position
3 current flows away from the commutator in the white half and
toward the commutator in the black half. Current has reversed
direction in the conductor. This is known as commutation.
19
Types of DC Motors
The field of DC motors can be a permanent magnet, or
electromagnets connected in series, shunt, or compound.
Permanent Magnet Motors
The permanent magnet motor uses a magnet to supply field
flux. Permanent magnet DC motors have excellent starting
torque capability with good speed regulation. A disadvantage
of permanent magnet DC motors is they are limited to the
amount of load they can drive. These motors can be found on
low horsepower applications. Another disadvantage is that
torque is usually limited to 150% of rated torque to prevent
demagnetization of the permanent magnets.
Series Motors
In a series DC motor the field is connected in series with the
armature. The field is wound with a few turns of large wire
because it must carry the full armature current.
A characteristic of series motors is the motor develops a large
amount of starting torque. However, speed varies widely
between no load and full load. Series motors cannot be used
where a constant speed is required under varying loads.
Additionally, the speed of a series motor with no load increases
to the point where the motor can become damaged. Some load
must always be connected to a series-connected motor. Seriesconnected motors generally are not suitable for use on most
variable speed drive applications.
20
Shunt Motors
In a shunt motor the field is connected in parallel (shunt) with
the armature windings. The shunt-connected motor offers good
speed regulation. The field winding can be separately excited or
connected to the same source as the armature. An advantage
to a separately excited shunt field is the ability of a variable
speed drive to provide independent control of the armature and
field. The shunt-connected motor offers simplified control for
reversing. This is especially beneficial in regenerative drives.
Compound Motors
Compound motors have a field connected in series with the
armature and a separately excited shunt field. The series field
provides better starting torque and the shunt field provides
better speed regulation. However, the series field can cause
control problems in variable speed drive applications and is
generally not used in four quadrant drives.
21
Speed/Torque Curves
The following chart compares speed/torque characteristics of
DC motors. At the point of equilibrium, the torque produced
by the motor is equal to the amount of torque required to
turn the load at a constant speed. At lower speeds, such as
might happen when load is added, motor torque is higher than
load torque and the motor will accelerate back to the point of
equilibrium. At speeds above the point of equilibrium, such as
might happen when load is removed, the motor’s driving torque
is less than required load torque and the motor will decelerate
back to the point of equilibrium.
Review 2
1.
The field in larger DC motors is typically an ___________
_.
2. Whenever ____________ flows through a conductor a
magnetic field is generated around the conductor.
3. Voltage induced into the conductors of an armature
that is in opposition to the applied voltage is known as
____________ .
4. Identify the following motor types.
a
b
22
c
d
DC Motor Ratings
The nameplate of a DC motor provides important information
necessary for correctly applying a DC motor with a DC drive.
The following specifications are generally indicated on the
nameplate:
•
•
•
•
•
•
•
•
•
•
HP
Manufacturer’s Type and Frame Designation
Horsepower at Base Speed
Maximum Ambient Temperature
Insulation Class
Base Speed at Rated Load
Rated Armature Voltage
Rated Field Voltage
Armature Rated Load Current
Winding Type (Shunt, Series, Compound,
Permanent Magnet)
Enclosure
Horsepower is a unit of power, which is an indication of the
rate at which work is done. The horsepower rating of a motor
refers to the horsepower at base speed. It can be seen from
the following formula that a decrease in speed (RPM) results in
a proportional decrease in horsepower (HP).
23
Armature Speed, Volts, and Amps
Typically armature voltage in the U.S. is either 250 VDC or
500 VDC. The speed of an unloaded motor can generally be
predicted for any armature voltage. For example, an unloaded
motor might run at 1200 RPM at 500 volts. The same motor
would run at approximately 600 RPM at 250 volts.
The base speed listed on a motor’s nameplate, however, is an
indication of how fast the motor will turn with rated armature
voltage and rated load (amps) at rated flux (Φ).
The maximum speed of a motor may also be listed on the
nameplate. This is an indication of the maximum mechanical
speed a motor should be run in field weakening. If a maximum
speed is not listed the vendor should be contacted prior to
running a motor over the base speed.
Winding
24
The type of field winding is also listed on the nameplate. Shunt
winding is typically used on DC Drives.
Field Volts and Amps
Shunt fields are typically wound for 150 VDC or 300 VDC. Our
sample motor has a winding that can be connected to either
150 VDC or 300 VDC.
Field Economizing
In many applications it may be necessary to apply voltage to
the shunt field during periods when the motor is stationary and
the armature circuit is not energized. Full shunt voltage applied
to a stationary motor will generate excessive heat which will
eventually burn up the shunt windings. Field economizing is a
technique used by DC drives, such as the SIMOREG® 6RA70,
to reduce the amount of applied field voltage to a lower level
when the armature is de-energized (standby). Field voltage
is reduced to approximately 10% of rated value. A benefit of
field economizing over shuting the field off is the prevention of
condensation.
Insulation Class
The National Electrical Manufacturers Association (NEMA)
has established insulation classes to meet motor temperature
requirements found in different operating environments. The
insulation classes are A, B, F, and H.
Before a motor is started the windings are at the temperature
of the surrounding air. This is known as ambient temperature.
NEMA has standardized on an ambient temperature of 40°C
(104°F) for all classes.
25
Temperature will rise in the motor as soon as it is started. The
combination of ambient temperature and allowed temperature
rise equals the maximum winding temperature in a motor. A
motor with Class F (commonly used) insulation, for example,
has a maximum temperature rise of 105°C. The maximum
winding temperature is 145°C (40°C ambient + 105°C rise).
A margin is allowed to provide for a point at the center of the
motor’s windings where the temperature is higher. This is
referred to as the motor’s hot spot.
The operating temperature of a motor is important to efficient
operation and long life. Operating a motor above the limits of
the insulation class reduces the motor’s life expectancy. A 10°C
increase in the operating temperature can decrease the life
expectancy of a motor by as much as 50%. In addition, excess
heat increases brush wear.
26
Speed/Torque Relationships of Shunt
Connected Motors
An understanding of certain relationships within a DC motor
will help us understand the purposes of various the functions in
a DC drive discussed later in the course. The formulas given in
the following discussion apply to all three types of DC motors
(series, shunt, and compound). However, The focus will be on
shunt connected DC motors because these motors are more
commonly used with DC drives.
DC Motor Equations
In a DC drive, voltage applied (Va) to the armature circuit is
received from a variable DC source. Voltage applied to the field
circuit (Vf) is from a separate source. The armature of all DC
motors contains some amount of resistance (Ra). When voltage
is applied (Va), current (Ia) flows through the armature. You will
recall from earlier discussion that current flowing through the
armature conductors generates a magnetic field. This field
interacts with the shunt field (Φ) and rotation results.
Armature Voltage
The following armature voltage equation will be used to
demonstrate various operating principles of a DC motor.
Variations of this equation can be used to demonstrate how
armature voltage, CEMF, torque, and motor speed interact.
Va = (KtΦn) + (IaRa)
Where:
Va = Applied Armature Voltage
Kt = Motor Design Constants
Φ = Shunt Field Flux
n = Armature Speed
Ia = Armature Current
Ra = Armature Resistance
27
CEMF
As previously indicated, rotation of the armature through
the shunt field induces a voltage in the armature (Ea) that
is in opposition to the armature voltage (Va). This is counter
electromotive force (CEMF).
CEMF is dependent on armature speed (n) and shunt field (Φ)
strength. An increase in armature speed (n) or an increase of
shunt field (Φ) strength will cause a corresponding increase in
CEMF (Ea).
Ea = KtΦn or Ea = Va - (IaRa)
Motor Speed The relationship between VA and speed is linear as long as flux
(Φ) remains constant. For example, speed will be 50% of base
speed with 50% of VA applied.
Motor Torque
The interaction of the shunt and armature field flux produces
torque (M). An increase in armature current (Ia) increases
armature flux, thereby increasing torque. An increase in field
current (If) increases shunt field flux (Φ), thereby increasing
torque.
M ≈ IaΦ
Constant Torque 28
Base speed corresponds to full armature voltage (Va) and full
flux (Φ). A DC motor can operate at rated torque (M) at any
speed up to base speed, by selecting the appropriate value
of armature voltage. This is often referred to as the constant
torque region. Actual torque (M) produced, however, is
determined by the demand of the load (Ia).
Constant Horsepower
Some applications require the motor to be operated above base
speed. Armature voltage (Va), however, cannot be higher than
rated nameplate voltage. Another method of increasing speed
is to weaken the field (Φ). Weakening the field reduces the
amount of torque (M) a motor can produce. Applications that
operate with field weakening must require less torque at higher
speeds.
Horsepower is said to be constant because speed (N) increases
and torque (M) decreases in proportion.
Field Saturation
It can be seen from the speed (n) and torque (M) formulas that
field flux (Φ) density has a direct effect on motor speed and
available torque. An increase in field flux (Φ), for example, will
cause a decrease in speed (n) and an increase in available motor
torque (M).
29
The relationship between field current (If) and flux (Φ) is not as
directly proportional as it may appear. As flux density increases
the field’s ability to hold additional flux decreases. It becomes
increasingly difficult to increase flux density. This is known as
saturation.
A saturation curve, such as the example shown below,
can be plotted for a DC motor. Flux (Φ) will rise somewhat
proportionally with an increase of field current (If) until the knee
of the curve. Further increases of field current (If) will result in
a less proportional flux (Φ) increase. Once the field is saturated
no additional flux (Φ) will be developed.
Review 3
1.
One way to increase motor speed is to ____________
armature voltage.
a.increase
b.decrease
2. CEMF is zero when the armature is ____________ .
a.turning at low speed
b.turning at max speed
c.not turning
d.accelerating
3. A ____________ - connected motor is typically used
with DC drives.
4. A DC motor, operating from zero to base speed, can
be said to be operating in the constant ____________
range.
a.horsepower
b.torque
5. No additional ____________ can be developed once the
field becomes saturated.
30
Basic DC Drives
The remainder of this course will focus on applying the
SIMOREG DC MASTER® 6RA70, to DC motors and associated
applications. The SIMOREG DC MASTER 6RA70 drives are
designed to provide precise DC motor speed control over
a wide range of machine parameters and load conditions.
Selection and ordering information, as well as engineering
information can be found in the SIMOREG 6RA70 DC MASTER
catalog, available from your Siemens sales representative.
SIMOREG drives are designed for connection to a three-phase
AC supply. They, in turn, supply the armature and field of
variable-speed DC motors. SIMOREG drives can be selected
for connection to 230, 400, 460, 575, 690, 830, and 950 VAC,
making them suitable for global use.
Siemens SIMOREG DC MASTER 6RA70 drives are available up
to 1000 HP at 500 VDC in standard model drives. In addition,
drives can be paralleled, extending the range up to 6000 HP.
Siemens SIMOREG drives have a wide range of
microprocessor-controlled internal parameters to control DC
motor operation. It is beyond the scope of this course to
cover all of the parameters in detail, however; many concepts
common to most applications and drives will be covered later in
the course.
31
Power Modules
The SIMOREG 6RA70 is available in a power module and base
drive panels. The power module contains the control electronics
and power components necessary to control drive operation
and the associated DC motor.
Base Drive Panels
The base drive panel consists of the power module mounted on
a base panel with line fuses, control transformer, and contactor.
This design allows for easy mounting and connection of power
cables.
32
High Horsepower Designs
High horsepower designs are also available with ratings up to
14,000 amps. These drives have input ratings up to 700 VAC
and can operate motors with armature ratings up to 750 VDC.
For additional information on high horsepower design SIMOREG
6RA70 DC MASTER drives, contact your Siemens sales
representative.
33
Converting AC to DC
Thyristor
A primary function of a DC drive, such as the SIMOREG 6RA70
DC MASTER, is to convert AC voltage into a variable DC
voltage. It is necessary to vary to DC voltage in order to control
the speed of a DC motor. A thyristor is one type of device
commonly used to convert AC to DC. A thyristor consists of an
anode, cathode, and a gate.
Gate Current
A thyristor acts as a switch. Initially, a thyristor will conduct
(switch on) when the anode is positive with respect to the
cathode and a positive gate current is present. The amount of
gate current required to switch on a thyristor varies. Smaller
devices require only a few milliamps; however, larger devices
such as required in the motor circuit of a DC drive may require
several hundred milliamps.
Holding Current
Holding current refers to the amount of current flowing from
anode to cathode to keep the thyristor turned on. The gate
current may be removed once the thyristor has switched on.
The thyristor will continue to conduct as long as the anode
remains sufficiently positive with respect to the cathode to
allow sufficient holding current to flow. Like gate current, the
amount of holding current varies from device to device. Smaller
devices may require only a few milliamps and larger devices
may require a few hundred milliamps.
The thyristor will switch off when the anode is no longer
positive with respect to the cathode.
34
AC to DC Conversion
The thyristor provides a convenient method of converting AC
voltage to a variable DC voltage for use in controlling the speed
of a DC motor. In this example the gate is momentarily applied
when AC input voltage is at the top of the sinewave. The
thyristor will conduct until the input’s sinewave crosses zero.
At this point the anode is no longer positive with respect to the
cathode and the thyristor shuts off. The result is a half-wave
rectified DC.
The amount of rectified DC voltage can be controlled by timing
the input to the gate. Applying current on the gate at the
beginning of the sinewave results in a higher average voltage
applied to the motor. Applying current on the gate later in the
sinewave results in a lower average voltage applied to the
motor.
DC Drive Converter
The output of one thyristor is not smooth enough to control
the voltage of industrial motors. Six thyristors are connected
together to make a 3Ø bridge rectifier. 35
Gating Angle
As we have learned, the gating angle of a thyristor in
relationship to the AC supply voltage, determines how much
rectified DC voltage is available. However, the negative and
positive value of the AC sine wave must be considered when
working with a fully-controlled 3Ø rectifier.
A simple formula can be used to calculate the amount of
rectified DC voltage in a 3Ø bridge. Converted DC voltage (VDC)
is equal to 1.35 times the RMS value of input voltage (VRMS)
times the cosine of the phase angle (cosα).
VDC = 1.35 x VRMS x cosα
The value of DC voltage that can be obtained from a 460 VAC
input is -621 VDC to +621 VDC. The following table shows
sample values of rectified DC voltage available from 0° to 180°.
It is important to note that voltage applied to the armature
should not exceed the rated value of the DC motor.
Volts RMS
460 VAC
460 VAC
460 VAC
460 VAC
460 VAC
460 VAC
460 VAC
a
0
30
60
90
120
150
180
Cosine
1.00
0.87
0.50
0.00
-0.50
-0.87
-1.00
Formula
VDC = 460 x 1.35 x 1
VDC = 460 x 1.35 x 0.87
VDC = 460 x 1.35 x 0.50
VDC = 460 x 1.35 x 0
VDC = 460 x 1.35 x (-0.50)
VDC = 460 x 1.35 x (-0.87)
VDC = 460 x 1.35 x (- 1)
VDC
621
538
310.5
0
-310.5
-538
-621
The following illustration approximates the output waveform
of a fully controlled thyristor bridge rectifier for 0°, 60°, and
90°. The DC value is indicated by the heavy horizontal line. It is
important to note that when thyristors are gated at 90° the DC
voltage is equal to zero. This is because thyristors conduct for
the same amount of time in the positive and negative bridge.
The net result is 0 VDC. DC voltage will increase in the negative
direction as the gating angle (α) is increased from 90° to a
maximum of 180°.
36
Review 4
1.
An increase of torque causes a corresponding ________
____ in horsepower
a.increase
b.decrease
2. Typically, DC motor armature voltage is either rated for
____________ VDC or ____________ VDC.
3. Identify the following insulation classes.
4. The SIMOREG 6RA70 DC MASTER ____________ drive
consists of the power module mounted on a panel with
line fuses, control transformer, and a contactor.
5. A thyristor is one type of device commonly used to
convert ____________ .
a.DC to AC
b.AC to DC
6. The approximate converted DC voltage of a six-pulse
converter when the thyristors are gated at 30° is ______
______ VDC.
37
Basic Drive Operation
Controlling a DC Motor
A thyristor bridge is a technique commonly used to control the
speed of a DC motor by varying the DC voltage. Examples of
how a DC rectifier bridge operates are given on the next few
pages. Voltage values given in these examples are used for
explanation only. The actual values for a given load, speed, and
motor vary.
It is important to note that the voltage applied to a DC motor
be no greater than the rated nameplate. Armature windings
are commonly wound for 500 VDC. The control logic in the
drive must be adjusted to limit available DC voltage to 0 - 500
VDC. Likewise, the shunt field must be limited to the motor’s
nameplate value. 38
Basic Operation
A DC drive supplies voltage to the motor to operate at a desired speed. The motor draws current from this power source in
proportion to the torque (load) applied to the motor shaft.
100% Speed, 0% Load
In this example an unloaded motor connected to a DC drive is
being operated at 100% speed. The amount of armature current
(Ia) and unloaded motor needs to operate is negligible. For the
purpose of explanation a value of 0 amps is used.
The DC drive will supply only the voltage required to operate
the motor at 100% speed. We have already learned the amount
of voltage is controlled by the gating angle (COSα) of the
thyristors. In this example 450 VDC is sufficient. The motor
accelerates until CEMF reaches a value of Va - IaRa. Remember
that Va = IaRa + CEMF. In this example IaRa is 0, therefore CEMF
will be approximately 450 VDC.
39
100% Speed, 100% Load
A fully loaded motor requires 100% of rated armature current at
100% speed. Current flowing through the armature circuit will
cause a voltage drop across the armature resistance (Ra). Full
voltage (500 VDC) must be applied to a fully loaded motor to
operate at 100% speed. To accomplish this, thyristors are gated
earlier in the sine wave (36.37°).
The DC drive will supply the voltage required to operate the
motor at 100% speed. The motor accelerates until CEMF
reaches a value of Va - IaRa. Remember that Va = IaRa +
CEMF. In this example armature current (Ia) is 100% and Ra
will drop some amount of voltage. If we assume that current
and resistance is such that Ra drops 50 VDC, CEMF will be
450 VDC.
40
1 Quad, 4 Quad
Up to this point we have only looked at a drive in singlequadrant operation. A single-quadrant DC drive will have six
thyristors.
In the speed-torque chart there are four quadrants of operation
according to direction of rotation and direction of torque. A
four-quadrant DC drive will have twelve thyristors.
Single-Quadrant Operation
Single-quadrant drives only operate in quadrant I. Motor torque
(M) is developed in the forward or clockwise (CW) direction
to drive the motor at the desired speed (N). This is similar
to driving a car forward on a flat surface from standstill to a
desired speed. It takes more forward or motoring torque to
accelerate the car from zero to the desired speed. Once the
car is at desired speed your foot can be let off the accelerator
a little. When the car comes to an incline a little more gas,
controlled by the accelerator, maintains speed. To slow or stop
a motor in single-quadrant operation the drive lets the motor
coast.
41
Changing Direction of
a DC Motor
There are two ways to change the direction a DC motor
rotates.
1. Reverse Armature Polarity
2. Reverse Field Polarity
Reversing in Single-
Quadrant Operation
Field contactor reverse kits can be used to provide bidirectional
rotation from a single-quadrant drive. To turn the motor in the
forward direction the “F” contacts are closed, applying DC
voltage in one polarity across the shunt field. Simply reversing
the polarity of the field, by opening the “F” contacts and closing
the “R” contacts, will reverse direction of a DC motor.
It is important to note that field reversal will only work when a
quick reversal is not required. The field circuit is inductive and
must be brought to 0 current before opening the contacts.
Stopping a Motor
42
Stopping a motor in single-quadrant operation can be done by
simply removing voltage to the motor and allowing the motor to
coast to a stop. Alternatively, voltage can be reduced gradually
until the motor is at a stop. The amount of time required to stop
a motor depends on the inertia of the motor and connected
load. The more inertia the longer the time.
Dynamic Braking
Dynamic braking is often used on single quadrant drives as
a means of stopping a motor quickly. Dynamic braking is not
recommended for continuous or repetitive operation. Dynamic
braking kits for use with Siemens SIMOREG® drives are
typically designed to stop a load operating at base speed a
maximum of three consecutive times. After three consecutive
stops a waiting period of 15 minutes is required.
Dynamic braking develops stopping torque by using a contact
(MAUX) to connect a resistor (Rdb) across the armature terminals
after the drive controller turns off power to the motor. The
field remains energized to supply stopping torque. This is
because motor torque (M) depends on armature current (Ia)
and field flux (Φ).
Armature current (Ia) reverses direction as the motor now acts
like a generator. A reversal in armature current (Ia) results in a
reversal of torque applied to the motor. Torque, now applied
in the opposite direction, acts as a brake to the motor. Stored
energy in the rotating motor is applied across the resistor and
converted to heat. The resistor is sized to allow 150% current
flow initially. Armature voltage decreases as the motor slows
down, producing less current through the resistors. The motor is
finally stopped due to frictional torque of the connected load.
43
Four-Quadrant Operation
The dynamics of certain loads require four-quadrant operation.
If motor voltage is suddenly reduced, negative torque is
developed in the motor due to the inertia of the connected load.
The motor acts like a generator by converting mechanical power
from the shaft into electrical power which is returned to the
drive. This is similar to driving a car downhill. The car’s engine
will act as a brake. Braking occurs in quadrants II and IV.
Regen
In order for a drive to operate in all four quadrants a means must
exist to deal with the electrical energy returned by the motor.
Electrical energy returned by the motor tends to drive the DC
voltage up, resulting in excess voltage that can cause damage.
One method of getting four-quadrant operation from a DC drive
is to add a second bridge connected in reverse of the main
bridge. The main bridge drives the motor. The second bridge
returns excess energy from the motor to the AC line. This
process is commonly referred to as regen. This configuration is
also referred to as a 4-Quad design.
44
Motoring
100% Speed, -100% Load
The motor receives power from the incoming line. In this
example the motor is operating at full speed (500 VDC).
When the motor is required to stop quickly, the motoring bridge
shuts off and the regen bridge turns on. Due to the initial
inertia of the connected load the motor acts like a generator,
converting mechanical power at the shaft into electrical power
which is returned to the AC line. The IaRa voltage drop (-50
VDC) is of opposite polarity then when the drive was supplying
motoring power. The control logic is gating thyristors in the
regen bridge at an angle of 130° and the resultant DC voltage
on the bridge is 400 VDC, in the opposite polarity. Because the
regen bridge is of opposite polarity, the voltage applied to the
motor acts like an electrical brake for the connected load.
45
Regen vs. Dynamic Braking
Regen and dynamic braking provide the same amount of
braking power to slow a motor from maximum speed in field
weakening to base speed. This is because field strength
increases until the motor reaches base speed. However, from
base speed to stop, regen is capable of slowing a motor at a
faster rate. In addition, regen can develop torque at zero speed
to bring the motor to a complete stop.
Another advantage of regen is that regen braking is not limited
in duty cycle and cool-down periods. Applications that require
frequent braking or have overhauling loads should consider four
quadrant operation with regen braking.
Reversing
46
A four-quadrant drive can easily reverse the direction of rotation
of a DC motor simply by applying armature voltage in the
opposite polarity. This is accomplished by using what was the
regen bridge to motor. The bridge that was used to drive the
motor in the forward direction becomes the regen bridge.
Review 5
1.
When torque is developed in the forward direction and
the armature is turning in the forward direction, the
motor is operating in quadrant ____________ .
2. When the armature is turning in the forward direction
but torque is developed in the reverse direction, the
motor is operating in quadrant ____________ .
3. The direction of rotation of a DC motor, operated from
a 6-pulse converter, can be reversed by reversing the
polarity of the DC voltage applied to the ____________
field.
4. ____________ ____________ is a method used to stop a
motor quickly by applying a resistor to the armature.
5. Which of the following is an advantage of a 4-quad
converter?
a.Instead of being dissipated in heat, excess energy is
returned to the supply line.
b.From base speed to zero speed a 4-quad converter
will stop a motor faster than a 1-quad converter.
c.A 4-quad converter can reverse motor direction by
simply applying voltage in the opposite polarity
across the armature.
d.all of the above.
47
SIMOREG 6RA70 DC MASTER Electronics
Up to this point we have looked at the power components
of a DC Drive necessary to control the speed of a DC motor.
The actual control of these components is accomplished with
electronic hardware and technology software.
Speed Control with
CEMF Feedback
Speed control is one mode of operation. The drive will attempt
to maintain a constant speed regardless of the load’s torque.
A speed reference is input into a ramp function generator
which applies reference voltage to the speed controller over a
specified period of time. This allows a smoother acceleration
of the motor and connected load. The output of the speed
controller is routed to the firing circuit, which controls the
amount of voltage applied to the armature.
You will recall that Va (applied voltage) = IaRa + CEMF. IaRa is
proportional to load and is generally 10% of nameplate armature
voltage at 100% load. Therefore, as load torque/current varies
between 0 and 100%, IaRa varies from 0 to 50 VDC for a 500
VDC armature.
Va and Ia are constantly monitored. Ra is measured during the
comissioning and tuning of the drive. Because Va, Ia, and Ra are
known values, CEMF (Ea) can be precisely calculated. CEMF is
proportional to speed and the speed controller uses this value
to calculate actual speed. Speed control with CEMF feedback
can only be used on applications where the motor operates
between zero and base speed. CEMF feedback provides
approximately 2-5% speed regulation.
48
Speed Control with
Tach Feedback
A tachometer can be used when a more accurate
measurement of speed is needed, or when the motor will be
operated above base speed. A measurement of actual speed is
returned to the speed controller. The speed controller will make
armature voltage adjustments to maintain constant speed with
variations in load. If, for example, load is suddenly increased the
motor will slow, reducing speed feedback. The speed controller
will output a higher signal to the current controller, which
will increase the firing angle of the firing circuit. The resulting
increased armature voltage applies more torque to the motor
to offset the increased load. Motor speed will increase until it is
equal with the speed reference setpoint.
When the motor is rotating faster than desired speed armature
voltage is reduced. In a four-quad drive DC armature voltage
could momentarily be reversed to slow the motor at a faster
rate to the desired speed. Several tachs can be used with the
SIMOREG 6RA70. DC tachs provide approximately 0.10 to 2%
speed regulation. Digital (pulse) tachs provide at least 0.01%
speed regulation. These values vary depending on the tach and
the operating conditions.
49
Current Measurement
The drive monitors current, which is summed with the speed
control signal at the current controller. The drive acts to maintain
current at or below rated current by reducing armature voltage
if necessary. This results in a corresponding reduction in speed
until the cause of the overcurrent is removed.
Torque Control
Some applications require the motor to operate with a specific
torque regardless of speed. The outer loop (speed feedback) is
removed and a torque reference is input. The current controller
is effectively a torque controller because torque is directly
proportional to current.
Tuning the Drive
A feature of the SIMOREG 6RA70 DC MASTER is the ability to
self tune for a given motor and associated load. An improperly
tuned control may result in an excessive speed overshoot when
changing from one speed to another. Oscillations can occur
which contribute to system instability.
50
A properly tuned drive will have an initial overshoot of
approximately 43% and settle into a new speed quickly. This
provides a stable system with quick response.
The SIMOREG 6RA70 DC MASTER has five auto tune routines
to match the performance of the drive to the controlled motor
and associated load.
•
Pre-control and current controller for armature and field
•
Speed controller for mechanics of the system
•
Field weakening
•
Friction, windage, and inertia compensation for high
intertia loads
•
Optimization for drives with oscillating mechanical
components
51
CUD1 Board
The CUD1 board is the main control board for the SIMOREG
6RA70. This board contains the necessary software and
hardware interfaces for operating the drive in speed or
torque control. It has input and output connections for wiring
the control devices of various functions such as start/stop
pushbuttons and speed potentiometer. The CUD1 board has
comprehensive diagnostics for troubleshooting. CUD1 also
contains the necessary software for self-tuning.
Programmable binary outputs, used to indicate the condition of
the drive, are available on X171. Binary inputs are also available
to start and stop the drive on X171. In addition, there are two
programmable binary inputs for such functions as reverse and
jog. The 6RA70 accepts analog inputs for speed control on
X174. Programmable analog outputs on X175 provide meter
indication of various drive parameters such as current and
voltage. A motor temperature switch can be connected to X174
and is used to stop the drive if the motor becomes overheated.
Connections are also available on X173 for a digital tach.
52
Typical Connections
The following diagram shows a typical connection used to
operate the drive. A normally open (NO) contact is used to start
and stop the drive.
Alternately, pushbuttons can be used to start and stop the
drive.
53
Programming and
Operating Sources
SIMOREG 6RA70 drives can be programmed and operated
from various sources, such as the PMU, OP1S, or other
SIMATIC® HMI device such as the TP170A, TP170B, OP27,
or MP370. In addition to these, various methods of serial
communication is available through RS232 or RS485
connections. These will be discussed later in this section with
the option boards.
The PMU can be used alone or with the OP1S. The OP1S can
be mounted directly on the PMU or up to 200 meters away
with an external power supply. Parameters, such as ramp
times, minimum and maximum speed, and modes of operation
are easily set. The changeover key (“P”) toggles the display
between a parameter number and the value of the parameter.
The up and down pushbuttons scroll through parameters and
are used to select a parameter value, once the “P” key sets the
parameter. The OP1S has a numbered key pad for direct entry.
SIMATIC HMI Devices
54
Another, more robust option, is a SIMATIC HMI device such
as the TP170A. The TP170A uses a touch-sensitive screen
for control and monitoring. It is powered from the drive and
standard PROFIBUS connections.
CUD2 Expansion Board
The CUD2 is typically selected when additional inputs and
outputs (I/O) are required. CUD2 I/O is selectable. An advantage
to the CUD2 expansion board is that it mounts directly on the
CUD1 and requires no additional hardware. The CUD2 provides
four optically isolated binary inputs, four selectable binary
inputs to ground, two analog inputs, one analog input for motor
temperature evaluation, two binary outputs, and one serial
interface. In addition to the expanded I/O, the CUD2 provides a
parallel interface for paralleling up to six power modules.
55
EB1 and EB2 Expansion Boards
EB1 and EB2 are half-sized expansion boards that provide a
number of additional I/O possibilities. EB1 has three binary
inputs and four bidirectional binary I/O. Bidirectional I/O can
be configured as a binary input or output. One of the analog
inputs is used as a voltage or current reference input. Two of the
analog inputs can also be configured as binary inputs.
EB2 has two binary inputs, one analog input, one analog output,
and four relay contacts. Three of the contacts are normally open
(NO) and one of the contacts can be configured as normally
open (NO) or normally closed (NC).
I/O
Isolated Binary Inputs
Binary Inputs
Bidirectional Binary I/O
Analog Inputs
Analog Outputs
Relay (Binary) Outputs
Serial Interface
Parallel Converter Interface
T400 Technology Board
CUD2
4
4
0
2
2
2
1
1
EB1
0
3
4
3
2
0
0
0
EB2
0
2
0
1
1
4
0
0
The T400 is an option board that is used to provide specialized
features for applications, such as winders, tension control,
position control, and hoisting gear. In addition to applying
built-in technology functions, users familiar with the Siemens
PLC software SIMATIC STEP-7 can also implement their own
process functions.
To implement the various control functions required by specific
applications the T400 has two analog outputs, five analog
inputs, two binary outputs, eight binary inputs, four bidirectional
binary inputs/outputs, two incremental encoder inputs, and two
serial interfaces.
56
Communications
One of the strong points of the SIMOREG 6RA70 is its serial
interface capabilities, which makes it easy to integrate the drive
with other automation components. Communication options are
available for PROFIBUS-DP, SIMOLINK®, CAN, and DeviceNet
communications.
SLB
The SLB communication board is used for peer-to-peer
communication with other Siemens drives via SIMOLINK.
SIMOLINK is a high speed fiber optic ring bus that allows
various data to be passed from one drive to the next.
Communication is not limited to the SIMOREG 6RA70.
SIMOLINK can also communicate between Siemens AC drives
such as the MASTERDRIVE MC and MASTERDRIVE VC.
CBP2
PROFIBUS-DP is an open bus standard for a wide range
of applications in various manufacturing and automation
applications. Siemens DC drives can easily communicate with
other control devices such as programmable logic controllers
(PLCs) and personal computers (PCs) through the PROFIBUSDP communication system and other various protocols. The
CBP2 board is required to communicate via PROFIBUS-DP.
57
CBC
ISO is a federation of standards organizations from over 100
countries that develops voluntary standards for business,
science, and technology. The official name is Organization
Internationale de Normalisation, also known in the United
States as the International Organization for Standardization.
The CBC communication board is used to communicate with
CAN protocol, which is an ISO standard (ISO 11898) for serial
data communications. CAN protocol was initially developed in
1986 for the automotive industry. Today communication with
CAN protocol can also be found in other industrial automation
applications. One device, such as a PLC or computer, acts as a
master. SIMOREG drives equipped with CBC boards and other
controllable devices configured for CAN act as slaves. CAN
uses a simple twisted pair of wires for transmission of control
and parameter value data between SIMOREG drives with CBC
boards.
CBD
58
The CBD communication board is used to communicate with
DeviceNet. DeviceNet is another communication protocol
that was developed based on the CAN technology. DeviceNet
provides a low-level network for DeviceNet enabled devices
such as sensors, motor starters, and drives to communicate
with higher-level devices such as computers and PLCs.
DeviceNet can read the state of devices, such as on/off, as well
as start and stop motors (motor starters). SIMOREG 6RA70
DC MASTERs equipped with a CBD board can be added to a
DeviceNet network. A DeviceNet enabled master device can
control the operation, such as start, stop, accel, and decel.
SBP
Digital tachometers (encoders) can be used to measure the
actual speed of a motor. The SBP encoder board can be also
be used to monitor an external encoder, such as might be
connected to the driven machine.
Electronics Box
The electronics box contains the CUD1 board (main control
board) and option boards. The CUD1 board is plugged into
slot 1.
59
Mounting Option Boards
There are several option boards available, which will be
discussed later in this section. Option boards are automatically
recognized by the drive. Up to six boards can be installed in
the electronics box. A Local Bus Adapter (LBA) is required if
mounting positions 2 or 3 are needed. In addition, adapter
boards (ADB) are necessary for slots D, E, F, and G when
utilizing the half-size option boards.
There are a few rules that must be followed when mounting
option boards:
60
•
Option boards may be plugged into positions 2 or 3,
however, position 2 must be filled first.
•
When used, a technology board (T400) is always installed
in position 2.
•
If a communication board (CBP2, CBC. or CBD) is used
with a technology board the communication board is
placed in slot G.
•
It is unnecessary and not possible to use expansion
boards EB1 and EB2 in conjunction with the technology
board T400. T400 has its own expanded inputs and outputs
(I/O).
•
It is unnecessary and not possible to use the pulse
encoder board (SBP) or the SIMOLINK communication
board (SLB) in conjunction with T400. T400 has provision
to connect an encoder.
•
A maximum of two supplementary boards of the same
type may be used in one drive. For example, no more than
two communication boards or two expansion boards can
be used.
The following chart shows the mounting positions for CUD1 and
option boards.
Board
LBA
ADB
Location 1
CUD1
CUD2
CBP2
CBC
CBD
SLB
SBP
T400
EB1
EB2
No
No
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
No
No
Yes
Yes
Yes
Yes
Yes
No
Yes
Yes
Yes
Yes
No
No
No
No
No
No
No
No
Location 2
D
E
No
No
No
No
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Location 3
F
G
No
No
No
No
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
No
Yes
Yes
Yes
Yes
61
Review 6
1.
__________ is the designation of the main electronic
control board in the SIMOREG 6RA70 DC MASTER.
2. A _________ _________ _________ is required when
mounting option boards in the electronics box.
3. Position ________ must be filled first when installing
option boards.
4. ______ tuning tunes a drive to the motor characteristics.
5. Technology board T400 can be installed in location
_______.
6. The CUD2 expansion board mounts directly on _______
and requires no additional hardware.
7.
__________ expansion board has the most bidirectional
binary I/O.
a.CUD2 b. EB1 c. EB2
8. _________ is used to communicate with PROFIBUS-DP.
9. __________ is used to communicate with other
Siemens drives via SIMOLINK.
10. A second digital tachometer is connected to the drive
through an __________ board when T400 is not used.
62
Parameters and Function Blocks
The SIMOREG 6RA70 DC MASTER features an extensive
parameter set that can easily be adapted to almost any drive
task, from simple to complex. A wide scope of parameters
include:
•
•
•
•
•
•
Acceleration/Deceleration Control
Automatic Restart Function
Field Reversal
Various Arithmetic and Boolean Logic Operations
Technology Controllers
Velocity/Speed and Diameter Calculators
In addition, the SIMOREG 6RA70 DC MASTER has extensive
status indicators and display parameters for monitoring. The
SIMOREG 6RA70 DC MASTER also supports a large database
of faults and alarms. This provides the operator with a clear
indication of what may be needed to correct the problem.
There are numerous parameters within the SIMOREG 6RA70
DC MASTER. It is beyond the scope of this course to cover
these in any detail. However, it is important to understand how
parameters and function blocks work together.
Parameters
Parameter values are used to provide settings to the drive. In
the Siemens SIMOREG 6RA70 DC MASTER each parameter
is clearly designated by an assigned number. Parameters are
differentiated according to their function:
•
•
Function Parameters (can be read and written)
Visualization Parameters (can only be read)
63
Function Parameters
Acceleration or deceleration times are examples of function
parameters. A feature of DC drives is the ability to increase or
decrease the armature voltage gradually. This accelerates and
decelerates the motor smoothly with less stress on the motor
and connected load.
Parameters P303 and P304 work together to instruct the
SIMOREG 6RA70 DC MASTER how much acceleration/
deceleration time is needed from 0 to 100% speed. P303 and
P304 can be set to any value between 0.0 to 650 seconds.
If P303 were set to 20.00, for example, the drive would take
20 seconds to accelerate the motor from 0 to 100% speed.
Acceleration and deceleration time is linear which means the
time speed curve can be accurately tracked. The motor would
be at 25% speed after 5 seconds and 50% speed after 10
seconds.
Rounding is a feature that can be added to the acceleration/
deceleration curve. This feature smooths the transition between
starting and finishing a ramp.
64
Visualization Parameters
Visualization parameters are used for visualizing internal
quantities. These parameters are only displayed and cannot
be changed by the operator. Visualization parameters are
distinguished by a lower case “r”. Parameter r038, for example,
displays the value of voltage output to the motor.
Function Blocks
A function block consists of several parameters grouped
together to perform a specific task. The following function block
represents one example of how a proportional/integral (PI)
controller can be used in speed control of a SIMOREG 6RA70
DC MASTER.
Function Parameters
The response of a function block is determined by function
parameters. Proportional gain and integral time, for example,
determine the response of a PI-controller. Each parameter has
a name, identifying number, value range, and a factory setting.
Function parameters can be indexed. 65
Function and Bico Data Sets In many applications it may be desirable to configure the
SIMOREG 6RA70 DC MASTER for variations in operation.
For example, there may be a situation in an application where
it is desirable to have different acceleration times. Indexed
parameters can have up to four different values stored with
them. Each value stored is part of a data set. Parameter P303,
acceleration time, is an example of an indexed parameter. P303
can have four different acceleration times stored. P303 could,
for example, have the following values:
P303.1 = 0.50
P303.2 = 1.00
P303.3 = 3.00
P303.4 = 8.00
If data set 1 is active, the acceleration time is 0.50 seconds. If
data set 2 is active, the acceleration time is 1.00 second. Data
sets are operator selected and can be changed at any time.
PI-Controller
PI-controllers are commonly used in drive technology. In our
example the desired speed and actual speed are input to a
summation point. The two signals are opposite in polarity.
When the actual speed is equal to the desired speed the
deviation, which is input into the PI-controller, is zero (0).
Whenever desired speed and actual speed are different there is
a deviation.
Changes in load on the motor, for example, can affect motor
speed. A sudden increase in load would cause the motor to
slow down. This would decrease the feedback from actual
speed and the deviation would become more positive. It is
also possible that the application may require the motor to slow
down or speed up. Until the motor reaches the new desired
speed there will be a deviation.
66
The PI-controller’s job is to make speed corrections quickly a minimal amount of overshoot and oscillation. Parameter
P225 (gain) and parameter P226 (time) are used to tune the
PI-controller’s performance. The end result should be a fast
response time with about a 43% initial overshoot. The motor
should then settle in to the new desired speed.
Connectors and Binectors
Connectors and binectors are elements used to exchange
signals between function blocks. Connectors are used to store
analog values. Analog values are stored in the form that is
represented by 16 bit or 32 bit words. Binectors are used to
store binary (digital) information.
Connectors and binectors are identified by a name and number.
Connectors with 16 bit resolution are identified with a “K”. Connectors with 32 bit resolution are identified with a “KK”.
Binectors are identified with a “B”.
67
BICO BICO is the term used to describe the method of connecting
function blocks together. This is performed with BInectors
and COnnectors. A connection between two function blocks
consists of a connector or binector and a BICO parameter. With
BICO parameters you can determine the sources of the input
signals of a function block. This allows the user to “softwire”
function blocks to meet specific application requirements.
Engineering Tools
There are several engineering tools available optionally. These
tools aid in programming, operating, troubleshooting, and
managing SIMOREG 6RA70 DC MASTER drives.
Drive Monitor
68
?????????
Drive ES
Drive ES is used to integrate Siemens drives with the SIMATIC
automation world. There are three Drive ES packages available.
Package
Description
Drive ES Basic
Structured similar to SIMOVIS allowing
commissioning, parameter handling, oscilloscope
readout, and fault evaluation. Based on STEP 7 for
integration into SIMATIC.
Drive ES Graphic
Provides graphic configuring of BICO function
blocks. Requires Drive ES Basic and a SIMATIC
programming tool called SIMATIC CFC.
Drive ES SIMATIC Provides function blocks and examples of SIMATIC
projects. Requires Drive ES Basic.
69
Applications
When applying a DC drive and motor to an application it
is necessary to know the horsepower, torque, and speed
characteristics of the load. The following chart shows typical
characteristics of various loads.
Loads generally fall into one of three categories:
Category
Description
The load is essentially the same throughout the
Constant Torque speed range. Hoisting gear and belt conveyors
are examples.
70
Variable Torque
The load increases as speed increases. Pumps
and fans are examples.
Constant
Horsepower
The load decreases as speed increases. Winders
and rotary cutting machines are examples.
Application Examples
The Siemens SIMOREG 6RA70 DC MASTER drives are
designed to handle the most challenging applications. The
following examples are just some of applications the SIMOREG
can be used on.
Winders/Coilers
DC motors offer superior characteristics at low speed for winder
and coiler operation and performance. In winder applications
maintaining tension at standstill is a very important operation.
DC motors offer a wide speed range at rated torque. On many
winder applications that run in an extended speed range a
smaller horsepower DC motor could do the same job as a larger horsepower AC motor.
71
Marine Applications
DC drives offer several advantages in marine applications.
Compact sizing is one of the biggest advantages. DC drives
also adapt well from generator supplies such as found in the
marine industry.
Crane/Hoist
DC offers several advantages in applications that operate at
low speed, such as cranes and hoists. Advantages include low
speed accuracy, short-time overload capability, size, torque
proving control, and load sharing.
72
Mining/Drilling
DC is often preferred in the high horsepower applications
required in the mining and drilling industry. DC drives offer
advantages in size and cost. They are rugged, dependable, and
proven in the industry.
Extruding
Extruding is a price competitive industry. DC offers economical
solutions in the 60 to 1000 HP range which is commonly used
in extruding applications.
73
Selecting a Siemens DC Drive
The following flow diagram, along with the selection charts, will
help you select the right DC drive for your application.
74
The following tables provide catalog numbers for SIMOREG DC
drives up to 1000 HP. For larger drives consult your Siemens
sales representative.
Power Module
Horsepower
240 VDC 500 VDC
3
7.5
7.5
15
15
30
25
60
40
75
60
125
75
150
125
250
150
300
250
500
700
1000
Rated Armature
(Amps DC)
15
30
60
100
140
210
255
430
510
850
1180
1660
Catalog Number
6RA7018-6FS22-0Z+X01
6RA7025-6FS22-0Z+X01
6RA7028-6FS22-0Z+X01
6RA7031-6FS22-0Z+X01
6RA7075-6FS22-0Z+X01
6RA7078-6FS22-0Z+X01
6RA7082-6FS22-0Z+X01
6RA7085-6FS22-0Z+X01
6RA7087-6FS22-0Z+X01
6RA7091-6FS22-0Z+X01
6RA7093-4GS22-0Z+X01
6RA7095-4GS22-0Z+X01
75
Power Module
Four Quad, Regen
Horsepower
240 VDC 500 VDC
3
7.5
7.5
15
15
30
25
60
40
75
60
125
75
150
125
250
150
300
250
500
700
1000
Rated Armature
(Amps DC)
15
30
60
100
140
210
255
430
510
850
1180
1660
Horsepower
240 VDC 500 VDC
3
7.5
7.5
15
15
30
25
60
40
75
60
125
75
150
125
250
150
300
250
500
700
1000
Rated Armature
(Amps DC)
15
30
60
100
140
210
255
430
510
850
1180
1660
Horsepower
240 VDC 500 VDC
3
7.5
7.5
15
15
30
25
60
40
75
60
125
75
150
125
250
150
300
250
500
700
1000
Rated Armature
(Amps DC)
15
30
60
100
140
210
255
430
510
850
1180
1660
Catalog Number
6RA7018-6FS22-0Z+X01
6RA7025-6FS22-0Z+X01
6RA7028-6FS22-0Z+X01
6RA7031-6FS22-0Z+X01
6RA7075-6FS22-0Z+X01
6RA7078-6FS22-0Z+X01
6RA7082-6FS22-0Z+X01
6RA7085-6FS22-0Z+X01
6RA7087-6FS22-0Z+X01
6RA7091-6FS22-0Z+X01
6RA7093-4GS22-0Z+X01
6RA7095-4GS22-0Z+X01
Base Drive
Signle Quad, Non-Regen
Catalog Number
6RA7013-2FS22-0
6RA7018-2FS22-0
6RA7025-2FS22-0
6RA7030-2FS22-0
6RA7072-2FS22-0
6RA7075-2FS22-0
6RA7077-2FS22-0
6RA7082-2FS22-0
6RA7083-2FS22-0
6RA7087-2FS22-0
6RA7091-2FS22-0
6RA7094-2FS22-0
Base Drive
Four Quad, Regen
76
Catalog Number
6RA7013-2FV62-0
6RA7018-2FV62-0
6RA7025-2FV62-0
6RA7030-2FV62-0
6RA7072-2FV62-0
6RA7075-2FV62-0
6RA7077-2FV62-0
6RA7082-2FV62-0
6RA7083-2FV62-0
6RA7087-2FV62-0
6RA7091-2FV62-0
6RA7094-2FV62-0
Review 7
1.
Parameters that can be read only are referred to as
____________ parameters.
2. A function block consists of several ____________
grouped together to perform a specific task.
3. ____________ is the term used to describe the method
of connecting function blocks together.
4. Winders are examples of ____________ ____________
applications.
5. Identify the category of the following speed, torque,
and horsepower graphs.
77
Review Answers
Review 1
1) SIMOREG; 2) 15; 3) 15; 4) b. Dividing Distance by Time;
5) force; 6) external force.
Review 2
1) electromagnet; 2) current; 3) CEMF;
4) a. Permanent Magnet, b. Compound, c. Shunt, d. Series.
Review 3
1) a. increase; 2) c. not turning; 3) shunt; 4) b. torque; 5 flux.
Review 4
1) a. increase; 2) 250 VDC or 500 VDC; 3) a. A, b. B, c. F, d. H;
4) base; 5) b. AC to DC; 6) 538.
Review 5
1) I; 2) II; 3) shunt; 4) Dynamic Braking; 5) d. all of the above.
Review 6
1) CUD1; 2) Local Bus Adapter; 3) 2; 4) Armature; 5) 2; 6) CUD1;
7) b. EB1; 8) CBP2; 9) SLB; 10) SBP.
Review 7
1) visualization; 2) parameters; 3) BICO; 4) constant
horsepower; 5) a. Constant Torque, Constant Horsepower,
Variable Torque.
78
Final Exam
The final exam is intended to be a learning tool. The book
may be used during the exam. A tear-out answer sheet is
provided. After completing the test, mail the answer sheet in for
grading. A grade of 70% or better is passing. Upon successful
completion of the test a certificate will be issued. Those
receiving a score of less than 70% will be provided a second
test.
Questions
1.
The type of DC motor best suited for use with DC
drives is the ____________ wound motor.
a.
b.
c.
d.
2.
____________ is the trade name for Siemens DC drives.
a.
b.
3.
The base speed of a motor is an indication of how fast
the motor will turn with rated ____________ and
rated load (amps) at rated flux (Φ).
a.
b.
c.
d.
4.
A decrease in field flux strength (Φ) causes a/an
____________ .
a.
b.
c.
d.
series
shunt
compound
series or shunt
SIMOREG
SIMOVERT
c.
d.
SIMOVIS
SIMOLINK
armature voltage
CEMF
field current (If)
armature resistance (Ra)
decrease in armature voltage
increase in armature voltage
increase in motor torque
decrease in motor torque
79
80
5.
____________ is the voltage induced into an armature
conductor of a DC motor in opposition to applied
voltage.
a.
b.
c.
d.
6.
____________ current refers to the minimum amount
of current flowing from anode to cathode to keep a
thyristor turned on.
a.
d.
c.
d.
7.
The value of rectified DC voltage obtained from a
460 VAC 3Ø source when the thyristors are gated at
60° is ____________ VDC.
a.
b.
c.
d.
8.
A 1-quad drive uses ____________ thyristors to convert
AC to a variable voltage DC.
a.
b.
9.
____________ is a method sometimes used on
1-quad drives as a means of stopping a motor quickly
by converting mechanical energy to heat.
a.
b.
c.
d.
Armature voltage
Field voltage
CEMF
EMF
Armature current
Gating current
Holding current
Field current
0
310.5
538
621
4
6
Regen
Field reversal
Dynamic Braking
Armature reversal
c.
d.
8
12
10.
Which of the following is not an advantage of regen
over dynamic braking?
a.
b.
c.
d.
Regen brakes faster from max speed to
base speed
Regen brakes faster from base speed to stop
Regen is not limited to duty cycle and cooldown periods
Regen can develop torque at zero speed
11.
____________ tuning tunes the 6RA70 drive to the
motor characteristics.
a.
b.
12.
____________ is the main control board in the
6RA70 which controls drive operation.
a.
b.
13.
CUD2 requires ____________ to install in the 6RA70.
a.
b.
c.
d.
14.
If a communication board (CBP2, CBC, or CBD) is
used with a technology board, the communication
board must be placed in slot ____________ .
a.
b.
15.
The command to start the 6RA70 drive is received on
____________ of CUD1.
a.
b.
c.
d.
Speed
Armature
CUD1
CUD2
c.
d.
c.
d.
CEMF
Field
SLB
CBP2
ADB Adapter Board
LBA Local Bus Adapter
ADB and LBA
No additional hardware
D
E
c.
d.
F
G
Terminal 106 of XS
Terminal 4 of X174
Terminal 37 of X171
Terminal 14 of X175
81
82
16.
Hoisting gear is an example of a ____________ load.
a.
b.
c.
d.
17.
____________ is used to communicate with
PROFIBUS-DP.
a.
b.
18.
____________ is the term used to describe the method
of connecting function blocks together.
a.
b.
19.
____________ is an example of a visualization
parameter.
a.
b.
20.
The correct catalog number for a SIMOREG 6RA70
DC MASTER, base drive, four quad, to be used with
armature amps rated for 100 amps is ____________ .
a.
b.
c.
d.
constant torque
variable torque
constant horsepower
constant speed
CBC
CBP2
SIMATIC
SIMOVIS
P225
r038
c.
d.
c.
d.
c.
d.
6RA7031-6FS22-0Z+X01
6RA7031-6FV62-0Z+X01
6RA7030-2FS22-0
6RA7030-2FV62-0
CBD
SBP
BICO
QuickStart
K165
B0205
83
quickSTEP Online Courses
quickSTEP online courses are available at http://www.sea.
siemens.com/step.
The quickSTEP training site is divided into three sections:
Courses, Downloads, and a Glossary. Online courses
include reviews, a final exam, the ability to print a certificate
of completion, and the opportunity to register in the
Sales & Distributor training database to maintain a record of
your accomplishments.
From this site the complete text of all STEP courses can be
downloaded in PDF format. These files contain the most recent
changes and updates to the STEP courses.
A unique feature of the quickSTEP site is our pictorial glossary.
The pictorial glossary can be accessed from anywhere within
a quickSTEP course. This enables the student to look up an
unfamiliar word without leaving the current work area.
84
Was this manual useful for you? yes no
Thank you for your participation!

* Your assessment is very important for improving the work of artificial intelligence, which forms the content of this project

Download PDF

advertisement