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4.4.1.1 U-Start
4.4.1.2 t-Start
The start voltage U-start determines the torque of the motor.
Low values produce soft starting and a higher thermal load of the motor.
If the voltage is too low, the motor may not start immediately. In this case,
the voltage should be set higher in order to avoid any unnecessary heating of
the motor.
The motor's torque is proportional to the square of the start voltage.
Because of this, voltages lower than 30 % of mains voltage U
recommended. This value corresponds to around 10 % of the starting torque
of a motor in direct mains operation. When using a star-delta configuration,
the motor will start with approximately 30 % of the starting torque.
￫
Set start voltage U-Start to a voltage that is high enough to
cause the motor to rotate immediately with the start command.
This will prevent unnecessary motor heating.
The t-Start starting time is used to set the time in which the motor voltage
will be increased from a starting value of U-Start to 100 % U
accelerating the motor smoothly. If this starting time is too long, the motor
and the soft starter will be subjected to high temperature loads. This can
cause the safety devices to trip. Because of this, the shortest possible
starting time should be selected.
￫
Depending on the load and duty cycle, more starts per hour may
be possible when using shorter start times. Conversely, longer
start times will mean fewer starts per hour.
The ramp times should always be configured in a way that makes sense for
the specific machine application at hand.
Examples:
•
With conveyor belts select a time so that the transported goods do not
topple.
•
With belt drives, the time should be selected so that the belts do not
slip.
Some drives (e.g. a motor in idle operation or unloaded drives) reach the
rated speed already at the beginning or during the soft start ramp. In this
case, the t-Start setting must be reduced in such a way that any unnecessary
motor heating will be avoided.
￫
Excessively short start times may lead to the internal relay being
overloaded.
DS7 Soft starter 09/16 MN03901001Z-EN www.eaton.com
4 Operation
4.4 Potentiometer settings
are not
LN
, therefore
LN
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