Mechanical Brakecontrol - Danfoss FC 300 Design Manual

FC 300 Design Guide
Placing the brake resistor externally offers the following advantages:
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The brake is protected against short-circuiting of the brake resistor, and the brake transistor is
monitored to ensure that short-circuiting of the transistor is detected. A relay/digital output can
be used for protecting the brake resistor against overloading in connection with a fault in the
adjustable frequency drive.
In addition, the brake makes it possible to read out the momentary power and the mean power
for the last 120 seconds. The brake can also monitor the power energizing and ensure that it does
not exceed a limit set in par. 2-12. In par. 2-13, select the function to carry out when the power
transmitted to the brake resistor exceeds the limit set in par. 2-12.
Overvoltage control (OVC)
tion in par. 2-17. This function is active for all units. The function ensures that a trip can be avoided
if the DC link voltage increases. This is done by increasing the output frequency to limit the voltage
from the DC link. It is a very useful function if, for example, the ramp-down time is too short
because tripping the adjustable frequency drive is avoided. In this situation, the ramp-down time
is extended.

3.8.1. Mechanical Brakecontrol

For hoisting applications, it is necessary to be able to control an electro-magnetic brake. For con-
trolling the brake, a relay output (relay1 or relay2) or a programmed digital output (terminal 27
or 29) is required. Normally, this output must be closed for as long as the adjustable frequency
drive is unable to 'hold' the motor, due to a load that is too large, for example. In par. 5-40 (Array
parameter), par. 5-30, or par. 5-31 (digital output 27 or 29), select
for applications with an electro-magnetic brake.
When
start until the output current is above the level selected in par. 2-20
stop, the mechanical brake will close when the speed is below the level selected in par. 2-21
Activate Brake Speed [RPM]
i.e., an overvoltage situation, the mechanical brake immediately cuts in. This is also the case
during safe stop.
The brake resistor can be selected on the basis of the application in question.
The braking energy can be dissipated outside the control panel, i.e., where the energy
can be utilized.
The electronics of the adjustable frequency drive will not overheat if the brake resistor
is overloaded.
NOTE
Monitoring the braking energy is not a safety function; a thermal switch is required
for that purpose. The brake resistor circuit is not protected against ground leakage.
(exclusive brake resistor) can be selected as an alternative brake func-
Mechanical brake control
[32] is selected, the mechanical brake relay stays closed during
. If the adjustable frequency drive is brought into an alarm condition,
MG.33.B9.22 - VLT ® is a registered Danfoss trademark.
3. Introduction to FC 300
Mechanical brake control
[32]
Release Brake Current
. During
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