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NOTE!
If a short circuit in the brake transistor occurs, power dissipation in the brake resistor is only prevented by using a line switch or
contactor to disconnect the line power for the adjustable frequency drive. (The contactor can be controlled by the adjustable frequency
drive).
NOTE!
Do not touch the brake resistor, as it can get very hot during/after braking. The brake resistor must be placed in a secure environment
to avoid fire risk.
3.8.4 Control with Brake Function
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 latest 120 seconds. The brake can also monitor
the power energizing and make sure it does not exceed a limit selected in par. 2-12
Brake Power Limit (kW)
. In par. 2-13
Brake Power Monitoring
, select
the function to carry out when the power transmitted to the brake resistor exceeds the limit set in par. 2-12
Brake Power Limit (kW)
.
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.
Overvoltage control (OVC)
(exclusive brake resistor) can be selected as an alternative brake function in par. 2-17
Over-voltage Control
. 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, e.g., if the ramp-down time is too short since tripping of the adjustable frequency drive is
avoided. In this situation, the ramp-down time is extended.
3.9.1 Mechanical Brake Control
For hoisting applications, it is necessary to be able to control an electro-magnetic brake. For controlling 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
Function Relay
(Array parameter), par. 5-30
Terminal 27 Digital Output
, or
par. 5-31
Terminal 29 digital Output
, select
mechanical brake control
[32] for applications with an electro-magnetic brake.
When
mechanical brake control
[32] is selected, the mechanical brake relay stays closed during start until the output current is above the level selected
in par. 2-20
Release Brake Current
. During stop, the mechanical brake will close when the speed is below the level selected in par. 2-21
Activate Brake
Speed [RPM]
. If the adjustable frequency drive is brought into an alarm condition, i.e. an overvoltage situation, the mechanical brake immediately cuts
in. This is also the case during safe stop.
FC 300 Design Guide
3 Introduction to AutomationDrive FC 300
MG.33.BC.22 - VLT
®
is a registered Danfoss trademark
3-31
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