Siemens SIRIUS 3RW40, Manual

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Functions
5.2 Stop modes
SIRIUS 3RW30 / 3RW40
Manual, 01/2010, 535 1995-02 DS01
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5.2.1 Stop without load (3RW30 and 3RW40)
"Stop without load" means the power supplied to the motor via the soft starter is interrupted
when the ON command is removed from the starter. The motor coasts to a standstill, driven
only by the mass inertia (centrifugal mass) of the rotor and load. This is also referred to as a
natural stop. A large centrifugal mass means a longer stop time without load.
Typical applications for stop without load
Stop without load is used for loads that place no special demands on the startup
characteristic, e.g. fans.
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.
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