Siemens SINAMICS S120 - Brake Resistances (Armature Short-Circuit Braking); Function Description

Motor components
6.4 Brake resistances (armature short-circuit braking)
Synchronous Motors 1FK7
84 Configuration Manual, (PFK7S), Edition 12.2006, 6SN1197-0AD16-0BP1
6.4 Brake resistances (armature short-circuit braking)
6.4.1 Function description
For transistor PWM converters, when the DC link voltage values are exceeded or if the
electronics fails, then electrical braking is no longer possible. If the drive which is coasting
down, can represent a potential hazard, then the motor can be braked by short-circuiting
the armature. Armature short-circuit braking should be initiated at the latest by the limit
switch in the traversing range of the feed axis.
The friction of the mechanical system and the switching times of the contactors must be
taken into account when determining the distance that the feed axis takes to come to a
complete stop. In order to avoid mechanical damage, mechanical stops should be located
at the end of the absolute traversing range.
For servomotors with integrated holding brake, the holding brake can be simultaneously
applied to create an additional braking torque – however, with some delay.
Caution
The drive converter pulses must first be canceled and this actually implemented before
an armature short-circuit contactor is closed or opened. This prevents the contactor contacts
from burning and eroding and destroying the drive converter.
Warning
The drive must always be operationally braked using the setpoint input. For additional
information, refer to the Drive Converter Configuration Manual.
The optimum braking torque of the servomotor in regenerative operation can be obtained
using armature short-circuit with a matching external resistor circuit.
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Figure 6-6 Circuit (schematic) with brake resistors