Siemens 3RW44 Manual page 132

Industrial control soft starters
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Device functions
7.3 Coasting methods
DC braking torque
The motor's brake force can be set with the amount of the DC braking torque. The dynamic
braking torque must be increased if the motor is to accelerate again during DC braking.
Coast-down time
The coast-down time specifies the period during which the DC braking torque is to be
generated on the motor. The chosen braking time should be long enough to bring the load to
a standstill. To achieve an adequate braking effect down to standstill, the centrifugal mass
(J) of the load should not exceed that of the motor. The length of the coast-down time should
be chosen so that the motor comes to a standstill. Standstill detection does not take place in
the soft starter and, if required, must be realized by means of external measures.
Note
The real coast-down time can vary during braking operations when the combined braking
function is applied.
Figure 7-8
DC braking coasting method
When the DC braking function is selected, the coast-down time and DC braking torque can
be set on the starter. In this braking variant, one output of the soft starter must be changed
over to DC braking, through which an external braking contactor is controlled. You will find
suggested circuits in chapter Typical circuit diagrams (Page 216).
The ideal parameters must be set on the machine under applicable load conditions.
132
Combined braking
Manual, 03/2017, NEB535219502000/RS-AB/008
3RW44 soft starters

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