Safe Brake Control - Siemens SINAMICS G130 Engineering Manual

General Engineering Information for SINAMICS
Engineering Information
Functional safety
The Safe Torque Off function prevents the connected motor from starting accidentally from standstill or, in other
words, ensures the torque-free state of a rotating drive. A rotating axis loses its ability to brake.
When an electrical installation breaks down or stops, or when it needs to be serviced, repaired or cleaned, it must be
completely isolated from the power supply via the main circuit breaker.
The STO function does not isolate the installation from the supply system. It does not therefore provide any
protection against "electric shocks"!
Asynchronous motors cannot turn, even when more than one fault occurs.
In applications with synchronous motors, e.g. 1FT6 and 1FK6, it should be noted that limited movement can occur for
physical reasons when 2 faults occur in particular constellations.
Description of potential fault: Simultaneous breakdown of one power transistor in the upper inverter bridge and
another offset in the lower bridge ("positive arm" and "negative arm").
Maximum residual movement:
°
360
α
α = = 60 °
Synchronous rotary motors: e.g.: 1FT6, 6-pole motor;
max
max
Pole number of motor
In the case of synchronous linear motors, the maximum movement corresponds to the pole width.
In order to assess the potential hazard posed by critical residual movements, the machine manufacturer must
perform a safety evaluation.
With respect to permanent-magnet synchronous motors such as the 1FW4 torque motor, please note that the motor
terminals are under power when the rotor is turning (integrated permanent magnets). If the motors are driven
passively, voltage is induced in the motor even when the STO or SS1 functions are activated.
Separate protective mechanisms are recommended in such cases.

Safe Brake Control

General
The Safe Brake Control (SBC) function is designed to activate standstill brakes, which operate according to the
holding-current principle (e.g. motor standstill brakes). SINAMICS S120 Motor Modules in the Booksize format have a
corresponding connection. In order to use this function with S120 Power Modules in Blocksize format, a Safe Brake
Relay must be installed.
Operating principle
The brake is controlled by the Control Unit. There exist two signal paths for the closing of the brake. The command
for opening or closing the brake is transfered from the Control Unit via the DRIVE-CLiQ connection to the Motor
Module or the Power Module. The Motor Module or the Safe Brake Relay of the Power Module then acts and
activates the outputs for the brake accordingly.
For the Safe Brake Control function, the Motor Module takes over the control function and ensures that if the Control
Unit fails, the holding current of the brake is interrupted and the brake is closed. A malfunction of one of the two
switches (TB+ and TB-, see diagram below) will only be recognized by the brake diagnosis, if a change of status
occurs i.e. when opening or closing the brake. When a fault is recognized by either the Motor Module or the Control
Unit, the holding current of the brake will be interrupted and thus a safe status will be achieved.
SINAMICS Engineering Manual - May 2008
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© Siemens AG