Eaton DS7 Manual page 33

As well as the time-controlled startup of a motor, the DS7 soft starter also
enables a time-controlled reduction of the motor voltage and thus a
controlled stopping of the motor. This type of stop function is primarily used
for pumps in order to prevent pressure waves (water impact).
Jerky movements and therefore the wear on drive chains and drive belts as
well as bearings and gears can be reduced.
U
U-Start
t-Start
Figure 14: Time-based control of motor voltage with a soft starter
￫
The acceleration time of a drive with a soft starter always
depends on the load and the breakaway torques. The required
breakaway torque can be set via the start voltage (U-Start).
The ramp time (t-Start) for a linear voltage change should be as
short as possible. The ramp time for the deceleration (t-Stop)
must be greater than the load-dependent uncontrolled
deceleration time of the machine.
For the power semiconductors in the soft starter, the controlled
deceleration presents a similar load as the startup: If, for
example, the deceleration ramp is activated on a soft starter
with a maximum of 10 permissible starts per hour, the number
of permissible starts is reduced to 5 per hour (plus 5 stops
within this hour).
The output voltage of the soft starter determines the torque of the motor.
At machine startup it must therefore be ensured that the selected starting
voltage (U-Start) is not too low. Otherwise this may cause the motor to
overheat excessively before it starts up.
DS7 Soft starter 09/16 MN03901001Z-EN www.eaton.com
t
t-Stop
1 Device series DS7
1.14 Function
29