142
7 - THEORY OF OPERATION
TruTorque acceleration control can be very useful for a variety of applications. However it is best used to
start centrifugal pumps, fans, and other variable torque applications. TruTorque generally should not be used
in applications where the starting load varies greatly during the start such as with a reciprocating compressor,
where the starting load is very low, or where the starting load varies greatly from one start to another.
TruTorque control is not recommended for the starting of AC synchronous motors.
Initial Torque This parameter sets the initial torque level that the motor produces at the beginning of the starting ramp
profile. A typical value is 10% to 20%. If the motor starts too quickly or the initial motor torque is too high,
reduce this parameter. If the motor does not start rotating within a few seconds after a start is commanded,
increase this parameter. If the value is set too low a "No Current at Run" fault may occur.
Maximum Torque This parameter sets the final or maximum torque level that the motor produces at the end of the acceleration
ramp time. For a loaded motor, the maximum torque value initially should be set to 100% or greater. If the
maximum torque value is set too low, the motor may not produce enough torque to reach full speed and may
stall. On lightly loaded motors, this parameter may be reduced below 100% to produce smoother starts.
If the motor can be started by using the default TruTorque acceleration parameter values or another ramp
profile, the Maximum Torque level can be determined more precisely so that the motor comes up to speed in
approximately the preset ramp time. In this case, while the motor is running fully loaded, display the
TruTorque percent (TT%) meter on the display. Record the value displayed. The Maximum Torque level
should then be set to the recorded full load value of TT% plus an additional 10%. Restart the motor with this
value to verify correct operation.
z NOTE: When setting the Maximum Torque value, the motor must be monitored to ensure that the torque
level is high enough to allow the motor to reach full speed under worst-case load conditions.
z NOTE: Depending on loading, the motor many achieve full speed at any time during the TruTorque ramp.
This means that the Maximum Torque level many never be achieved. Therefore, the maximum torque level is
the maximum TruTorque level that is permitted. However the motor torque may not necessarily reach this
value during all starts.
Ramp Time When in TruTorque acceleration mode, the ramp time setting is the time it takes for the torque to go from the
initial torque setting to the maximum torque setting. To make the motor accelerate faster, decrease the ramp
time. To make the motor accelerate slower, increase the ramp time.
If the ramp time expires before the motor reaches full speed, the starter maintains the Maximum Torque level
until either the motor reaches full speed, UTS timer expires, or the motor thermal overload protection trips.
z NOTE: Setting the ramp time to a specific value does not necessarily mean that the motor takes that exact
amount of time to accelerate to full speed. The motor and load may achieve full speed before the ramp time
expires if the load does not require the set ramp time or set torque level to reach full speed. Alternately, the
motor and load may take longer than the set ramp time to achieve full speed depending on the parameter
settings and load level.
To Next Page
Loading...
Need help?
General
