Technical information

8 – THEORY OF OPERATION
Acceleration Control
119
If the ramp time expires before the motor reaches full speed, the starter maintains the maximum
current level until either the motor reaches full speed, the Up to Speed time expires, or the motor
thermal overload trips.
NOTE: Setting the ramp time to a specific value does not necessarily mean that the motor will take
this time to accelerate to full speed. The motor and load may achieve full speed before the ramp time
expires if the application does not require the set ramp time and maximum current to reach full speed.
Alternatively, the motor and load may take longer than the set ramp time to achieve full speed.
8.3.2 Programming A Kick Current
General
The kick current sets a constant current level that is applied to the motor before the ramp begins. The
kick current is only useful on motor loads that are hard to get rotating but then are much easier to
move once they are rotating. An example of a load that is hard to get rotating is a ball mill. The ball
mill requires a high torque to get it to rotate the first quarter turn (90°). Once the ball mill is past 90°
of rotation, the material inside begins tumbling and it is easier to turn.
Kick Level The kick current parameter is usually set to a low value and then the kick time is adjusted to get the
motor rotating. If the kick time is set to more than 2.0 seconds without the motor rotating, increase
the kick current by 100% and re-adjust the kick time.
Kick Time The kick time adjustment should begin at 0.5 seconds and be adjusted by 0.1 or 0.2 second intervals
until the motor begins rotating. If the kick time is adjusted above 2.0 seconds without the motor
rotating, start over with a higher kick current setting.
8.3.3 TruTorque Acceleration Control Settings and Times
General
TruTorque acceleration control is a closed loop torque based control. The primary purpose of
TruTorque acceleration control is to smoothly start motors and to reduce the torque surge that can
occur as an AC induction motor comes up to speed. This torque surge can be a problem in
applications such as pumps and belt driven systems. In pumping applications, this torque surge can
result in a pressure peak as the motor comes up to speed. In most situations this small pressure peak
is not a problem. However in selected cases, even a small pressure rise can be highly undesirable. In
belt driven applications, TruTorque can prevent the slipping of belts as the motor reaches full speed.
Figure 18 – TruTorque Ramp
Motor
Torque
Time
Kick Time Ramp Time
Up To Speed Timer
Motor Running
Torque
Initial Torque
Optional Kick
Current
Max Torque
Start command