CG Drives & Automation, 01-5980-01r2 Functionality 93
the original slope to accomplish a start within the set start
time. See Fig. 54.
Fig. 54 Torque ramp with current limit period.
Voltage ramp with current limit
The voltage period is increased linearly during the set start
time, from a value corresponding to the minimum allowed
voltage period plus the value set as start voltage, to full mains
voltage.
The current limit regulator is activated when the current is
reaching the chosen value in [335], to be switched off when
full output voltage is reached, or the start time has expired
[336].
Should the current fall to a value below the set current limit,
the current controller will be deactivated, and the voltage
ramp reactivated.
When the current limit controller is deactivated (below
current limit), the voltage ramp slope will increase above the
original slope to accomplish a start within the set start time.
Direct on-line start DOL with current limit
This could also be called “pure current limit start”.
As “Voltage ramp with Current limit” but with fixed ramp
time of 6 seconds.
Fig. 55 Direct on-line start in combination with current limit
at start.
If the regulator still is in active mode when the start time
expires, a “Current Limit” alarm is issued, and the alarm
action set in menu [236] is executed.
Start Time [336]
The start time is defined as the time during which a start
attempt is done. After the start time has elapsed, the TSA will
automatically go into bypass mode (exception: current limit
alarm condition). Make sure the start time is long enough for
your application so that the end reference value (e.g. [333]
EndTorqueSt for torque ramp) can be reached just before
start time has elapsed. This usually requires some trimming.
This menu is directly accessible for all start methods in menu
[331] except “DOL”. However, if combined with a current
limit in menu [335], the start time function is also available
for “DOL”.
Current
Start time
Limit period
End torque
Torque
Current limit
FLC
Ramp time (6 seconds)
Default: Off
Range: Off, 150 - 500% of I
n_mot
[224]
NOTE: Even though the current limit can be set as low as
150% of the nominal motor current value [224], this
minimum value cannot be used generally. If the current
limit is set too low in relation to the application’s
requirements, the motor will not be able to accelerate
the load.
NOTE: Check that the nominal motor current is set
properly in menu [224] if the current limit functionality is
used.
Default: 10 s
Range: 1 - 60 s
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