2 Product Overview
2.1 Description of the Brake System
When the speed reference of a frequency converter is
reduced, the motor acts as a generator and the frequency
converter brakes. When a motor acts as a generator, it
supplies energy to the frequency converter which is
collected in the DC link. The function of the brake resistor
is to provide a load on the DC link during braking, thereby
ensuring that the braking power is absorbed by the brake
resistor.
If a brake resistor is not used, the DC-link voltage of the
frequency converter continues to increase, until discon-
necting for protection. The advantage of using a brake
resistor is that it enables braking of a heavy load quickly,
e.g. on a conveyor belt.
The brake resistors in this series are all external
components. Therefore, the brake resistor does not form
an integral part of the frequency converter.
The external brake resistor provides the following
advantages:
•
The resistor time cycle can be selected as
required.
•
The heat developed during braking can be
conveyed beyond the panel cabinet to allow the
energy to be used.
•
The electronic components do not overheat, even
when the brake resistor is overloaded.
The brake resistor series is suitable for Danfoss frequency
converters
•
VLT
®
Micro Drive FC 51
•
VLT
®
HVAC Drive FC 102
•
VLT
®
AQUA Drive FC 202
•
VLT
®
AutomationDrive FC 300
•
VLT
®
AutomationDrive FC 360
•
VLT
®
Decentral Drive FCD 302
•
VLT
®
2800
.
2.2
Horizontal or Vertical Load
2.2.1 How to Select
The Danfoss brake resistor range consists of 2 groups:
•
Brake resistors for horizontal loads (conveyors,
trolleys, gantry cranes, etc.), see Illustration 2.1;
•
Brake resistors for vertical loads (cranes, hoists,
elevators), see Illustration 2.2.
Illustration 2.1 Horizontal Loads
Illustration 2.2 Vertical Loads
The brake resistor range is intended to cover the general
braking requirements for horizontal and vertical brake
applications.
To select the best brake resistor for an application, refer to
chapter 8.1 Selection Flow Chart. The flow chart links to
further information, either selection tables or calculations
of inertia or duty cycle.
To cater for both the horizontal and vertical ranges, 3
types of brake resistors are available:
•
Aluminium-housed flat-pack brake resistors
•
Aluminium-housed compact brake resistors
•
Steel grid brake resistors
Product Overview Design Guide
MG90O202 Danfoss A/S © Rev. 05/2014 All rights reserved. 5
2 2
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