Soft Stop (3Rw40 Only) - Siemens SIRIUS 3RW30 Manual

5.2.2

Soft stop (3RW40 only)

In "soft stop" mode, the natural stop process of the load is decelerated. The function is used
when the load must be prevented from stopping abruptly. This is typically the case in
applications with a low mass inertia or a high counter-torque.
Ramp-down time
The "Ramp-down time" potentiometer on the soft starter allows you to specify how long
power should still be supplied to the motor after the ON command is removed. The torque
generated in the motor is reduced by means of a voltage ramp function within this ramp-
down time and the application stops smoothly.
If the motor is stopped abruptly in pump applications, as is normal with wye-delta or direct
starting, for instance, water hammer can occur. Water hammer is caused by the sudden flow
separation, leading to pressure fluctuations on the pump. It has the effect of producing noise
and mechanical impacts on the pipelines as well as on any flaps and valves installed there.
Water hammer can be reduced compared to direct or wye-delta starting by using the SIRIUS
3RW40 soft starter. An optimum pump stop is achieved using a SIRIUS 3RW44 soft starter
with an integrated pump stop function (refer to chapter Comparison of device functions
(Page 30)).
Typical applications for soft stop
Use soft stop for
● Pumps to reduce water hammer.
● Conveyor belts to prevent the conveyed product from tilting.
SIRIUS 3RW30 / 3RW40
Manual, 10/2018, NEB535199502000/RS-AB/005
Functions
5.2 Stop modes
41