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.

DC+ DC-

1L1 L2 L3

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

Voltage

Control

Voltage

Control

– DC Bus

+ DC Bus

Voltage Dividers

Voltage

Divider

Voltage

Divider

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:

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