Lenze 8400 TopLine - Manual (Page 298)

5 Motor control (MCTRL)
5.13 Monitoring
298
Lenze · 8400 TopLine · Reference manual · DMS 6.0 EN · 06/2014 · TD05/TD14
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5.13.5 Brake resistor monitoring (I2xt)
Due to the converted braking power, the brake resistor is thermally stressed and can even be
thermally destroyed by excessive braking power.
The monitoring of the I
2
xt utilisation of the controller serves to protect the brake resistor. It acts in
proportion to the converted braking power.
• If the I 2 xt utilisation reaches the switch-off threshold set in C00572 :
• The error response set in C00574 will take place.
• The " oC12: I2xt brake resistor overload " error message is entered into the Logbook.
• The bMctrlBrakeChopperFault status output of the LS_DeviceMonitor system block will be set
to TRUE.
• If the system is dimensioned correctly, the monitoring should not be activated. If individual
pieces of rated data of the actually connected brake resistor are not known, they have to be
identified.
• If the DC-bus voltage exceeds the overvoltage threshold due to a braking energy that is too high,
the monitoring for overvoltage in the DC bus is activated ("OU: DC-bus overvoltage" error
message).
• Apart from the threshold of the I 2 xt utilisation that can be set in C00572 , there is the switching
threshold of the brake transistor which results from the mains voltage ( C00173 ) and the
reduced brake chopper threshold ( C00174 ).

Danger!
In the Lenze setting ( C00574 = "0: No Reaction"), the response of the monitoring function
does not stop the braking process!
In particular for applications such as hoists or applications with a DC-bus connection, it
must be checked if a stopping of the braking process due to a setting of C00574 = "1:
Fault" is permissible.

Stop!
Implement appropriate protective measures against thermal overload of the brake
resistor!
Examples:
• Parameterisation of an error response in C00574 and evaluation of the parameterised
error message within the application or the machine control system.
• Interruption of the mains supply by means of the temperature contact at the brake
resistor and a simultaneous activation of the mechanical brake.