Allen-Bradley 20A User manual

PowerFlex Dynamic Braking Resistor Calculator
Catalog Numbers 20A, 20B, 20F, 20G, 22A, 22B
Application Technique
Original Instructions

Important User Information
Read this document and the documents listed in the additional resources section about installation, configuration, and
operation of this equipment before you install, configure, operate, or maintain this product. Users are required to
familiarize themselves with installation and wiring instructions in addition to requirements of all applicable codes, laws,
and standards.
Activities including installation, adjustments, putting into service, use, assembly, disassembly, and maintenance are
required to be carried out by suitably trained personnel in accordance with applicable code of practice.
If this equipment is used in a manner not specified by the manufacturer, the protection provided by the equipment may
be impaired.
In no event will Rockwell Automation, Inc. be responsible or liable for indirect or consequential damages resulting from
the use or application of this equipment.
The examples and diagrams in this manual are included solely for illustrative purposes. Because of the many variables and
requirements associated with any particular installation, Rockwell Automation, Inc. cannot assume responsibility or
liability for actual use based on the examples and diagrams.
No patent liability is assumed by Rockwell Automation, Inc. with respect to use of information, circuits, equipment, or
software described in this manual.
Reproduction of the contents of this manual, in whole or in part, without written permission of Rockwell Automation,
Inc., is prohibited.
Throughout this manual, when necessary, we use notes to make you aware of safety considerations.
Labels may also be on or inside the equipment to provide specific precautions.
WARNING: Identifies information about practices or circumstances that can cause an explosion in a hazardous
environment, which may lead to personal injury or death, property damage, or economic loss.
ATTENTION: Identifies information about practices or circumstances that can lead to personal injury or death, property
damage, or economic loss. Attentions help you identify a hazard, avoid a hazard, and recognize the consequence.
IMPORTANT Identifies information that is critical for successful application and understanding of the product.
SHOCK HAZARD: Labels may be on or inside the equipment, for example, a drive or motor, to alert people that dangerous
voltage may be present.
BURN HAZARD: Labels may be on or inside the equipment, for example, a drive or motor, to alert people that surfaces may
reach dangerous temperatures.
ARC FLASH HAZARD: Labels may be on or inside the equipment, for example, a motor control center, to alert people to
potential Arc Flash. Arc Flash will cause severe injury or death.Wear proper Personal Protective Equipment (PPE). Follow ALL
Regulatory requirements for safe work practices and for Personal Protective Equipment (PPE).

Rockwell Automation Publication PFLEX-AT001L-EN-P - September 2017
Table of Contents
Preface
Waste Electrical and Electronic Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Product Safety . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Personal Safety. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Additional Resources. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Summary of Changes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Chapter 1
UnderstandingHowDynamicBraking
Works
How Dynamic Braking Works . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Dynamic Brake Components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Chapter 2
Determining Dynamic Brake
Requirements
How to Determine Dynamic Brake Requirements . . . . . . . . . . . . . . . . . . . . . . . . . 11
Determine Values of Equation Variables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Example Calculation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
Chapter 3
Evaluating the PowerFlex 7-Class
Internal Resistor
Evaluating the Capability of the Internal Dynamic Brake Resistor. . . . . . . . . . . 23
PowerFlex 70 Power Curves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
PowerFlex 700 Power Curves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
How to Evaluate a PowerFlex 750-Series Internal Resistor. . . . . . . . . . . . . . . . . . 32
Chapter 4
Selecting An External Resistor for
PowerFlex 7-Class Drives
How to Select an External Dynamic Brake Resistor for
PowerFlex 7-Class Drives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
Appendix A
Minimum Dynamic Brake Resistance. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71

4Rockwell Automation Publication PFLEX-AT001L-EN-P - September 2017
Table of Contents
Notes:

Rockwell Automation Publication PFLEX-AT001L-EN-P - September 2017 5
Preface
Read the General Precautions
Waste Electrical and
Electronic Equipment
Product Safety
Personal Safety
Additional Resources You can view or download publications at
http://www.rockwellautomation.com/global/literature-library/overview.page.
To place an order for paper copies of technical documentation, contact your
local Allen-Bradley distributor or Rockwell Automation® sales representative.
At the end of its life, this equipment should be collected separately from any
unsorted municipal waste.
ATTENTION: This drive contains ESD (Electrostatic Discharge) sensitive parts
and assemblies. Static control precautions are required when you install,
test, service, or repair this assembly. Component damage can result if ESD
control procedures are not followed. If you are not familiar with static control
procedures, reference any applicable ESD protection handbook.
ATTENTION: To avoid an electric shock hazard, verify that the voltage on the
bus capacitors has discharged completely before servicing.
ATTENTION: Measure the DC bus voltage at the power terminal block by
measuring between the +DC and -DC terminals or between the +DC and -
DC test point sockets if equipped. Also measure between the +DC terminal
or test point and the chassis, and between the -DC terminal or test point and
the chassis.The voltage must be zero for all three measurements.
2
0V
0V
DC+ DC-
1L1 L2 L3
O
I

6Rockwell Automation Publication PFLEX-AT001L-EN-P - September 2017
Preface
Summary of Changes This manual contains new and updated information as indicated in the
following table.
Topic Page
Added 200…240V AC definitions to Appendix A 67

Rockwell Automation Publication PFLEX-AT001L-EN-P - September 2017 7
Chapter 1
Understanding How Dynamic Braking Works
How Dynamic Braking Works When an induction motor’s rotor turns slower than the synchronous speed set by
the drive’s output power, the motor is transforming electrical energy obtained
from the drive into mechanical energy available at the drive shaft of the motor.
This process is referred to as motoring. When the rotor is turning faster than the
synchronous speed set by the drive’s output power, the motor is transforming
mechanical energy available at the drive shaft of the motor into electrical energy
that can be transferred back to the drive. This process is referred to as
regeneration.
Most AC PWM drives convert AC power from the fixed frequency utility grid
into DC power by means of a diode rectifier bridge or controlled SCR bridge
before it is inverted into variable frequency AC power. Diode and SCR bridges
are cost-effective, but can only handle power in the motoring direction.
Therefore, if the motor is regenerating, the bridge cannot conduct the necessary
negative DC current, the DC bus voltage increases and causes an overvoltage
fault at the drive. More complex bridge configurations use SCRs or transistors
that can transform DC regenerative electrical power into fixed frequency utility
electrical energy. This process is known as line regeneration.
A more cost-effective solution can be provided by allowing the drive to feed the
regenerated electrical power to a resistor which transforms it into thermal energy.
This process is referred to as dynamic braking.

8Rockwell Automation Publication PFLEX-AT001L-EN-P - September 2017
Chapter 1 Understanding How Dynamic BrakingWorks
Dynamic Brake Components A Dynamic Brake consists of a Chopper (the chopper transistor and related
control components are built into PowerFlex® drives) and a Dynamic Brake
Resistor.
Figure 1 shows a simplified Dynamic Braking schematic.
Figure 1 - Simplified Dynamic Brake Schematic
Chopper
The Chopper is the Dynamic Braking circuitry that senses rising DC bus voltage
and shunts the excess energy to the Dynamic Brake Resistor. A Chopper contains
three significant power components:
The Chopper Transistor is an Isolated Gate Bipolar Transistor (IGBT). The
Chopper Transistor is either ON or OFF, connecting the Dynamic Brake
Resistor to the DC bus and dissipating power, or isolating the resistor from the
DC bus. The most important rating is the collector current rating of the Chopper
Transistor that helps to determine the minimum resistance value used for the
Dynamic Brake Resistor.
Signal
Common
Dynamic
Brake
Resistor
Chopper
Transistor
Chopper Transistor
Voltage Control
To
Voltage
Control
To
Voltage
Control
– DC Bus
+ DC Bus
To
Voltage Dividers
Voltage
Divider
Voltage
Divider
FWD
FWD

Rockwell Automation Publication PFLEX-AT001L-EN-P - September 2017 9
Understanding How Dynamic BrakingWorks Chapter 1
Chopper Transistor Voltage Control regulates the voltage of the DC bus during
regeneration. The average values of DC bus voltages are:
Voltage dividers reduce the DC bus voltage to a value that is usable in signal
circuit isolation and control. The DC bus feedback voltage from the voltage
dividers is compared to a reference voltage to actuate the Chopper Transistor.
The Freewheel Diode (FWD), in parallel with the Dynamic Brake Resistor,
allows any magnetic energy stored in the parasitic inductance of that circuit to be
safely dissipated during turn off of the Chopper Transistor.
Resistor
The Resistor dissipates the regenerated energy in the form of heat. The
PowerFlex Family of Drives can use either the internal dynamic brake resistor
option or an externally mounted dynamic brake resistor wired to the drive.
Wiring
Frames 0…4
Wire to the DB resistor should be no longer than 10 feet from the drive
terminals. Wire should be twisted to minimize inductance.
Frames 5…6
Wire to the DB resistor should be no longer than 100 feet from the drive
terminals.
Drive Input Voltage Transistor Turn-On
Voltage
Maximum Power Calculation
Voltage
208 375V DC 395V DC
240 375V DC 395V DC
400 750V DC 790V DC
480 750V DC 790V DC
575 937.5V DC 987V DC
600 937.5V DC 987V DC
600 (Frame 5 and 6) 1076V DC 1135V DC
690 1076V DC 1135V DC

10 Rockwell Automation Publication PFLEX-AT001L-EN-P - September 2017
Chapter 1 Understanding How Dynamic BrakingWorks
Notes: