Braking transistor protective functions
With some inverters, the braking transistor can be monitored:
The „GTR7 OC“ protection function detects a short circuit at the braking resistor
terminals. Ground faults are not reliably detected by the internal protective circuit.
The so-called feedback signal (short-circuit / function monitoring of the transistor)
can be used to monitor whether the braking transistor is still switching. Whether the
inverter in question supports this protective function is listed in the installation man-
ual.
A short circuit at the braking resistor connections leads to error message 116 "ER-
ROR GTR7 OC". This error cannot be deactivated if the inverter has the appropri-
ate monitoring. A reset of this error is only possible after 1 second.
If the braking transistor cannot be switched on, the drive goes to 115 "ERROR
GTR7 always OFF". If the braking transistor cannot be switched off, the drive goes
to 117 "ERROR GTR7 always ON".
For all inverters that have the monitoring function in hardware, it is activated as
soon as the GTR7 functionality is30 = 1 "on“.
If the error "ERROR GTR7 always ON" is detected, the input thyristors of inverters
whose DC link is supplied via input thyristors are switched off.
Hazards and risks through ignorance!
➢ If the error "ERROR GTR7 always ON" occurs, the drive controller
must be disconnected from the mains supply within 5 minutes!
Load of the braking resistor in case of overvoltage
➢ The overvoltage level should never be exceeded when using a brak-
ing resistor. A motor accelerating uncontrollably due to errors, incor-
rect parameterisation (e.g. of the EMF) or incorrect adjustment of a
filter can lead to extreme overvoltage. If the regeneration by the appli-
cation is greater than it can be reduced by the braking resistor, the
overvoltage level can also be exceeded. This overload case must be
considered when selecting / protecting the resistor.
➢ Activation for too long (especially with input-dependent instead of
voltage-dependent control) can lead to overheating and destruction of
the braking resistor.
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