Mitsubishi Electric 800 Series Instruction Manual page 219

 Protecting equipment and limiting the load by the torque limit (Pr.277)
• Set Pr.277 Stall prevention operation current switchover = "1" to enable the torque limit.
• If the output torque (current equivalent to the torque) exceeds the stall prevention operation level, the output torque is
limited by adjusting the output frequency. The stall prevention operation level in such a case is based on the rating torque
of the motor.
NOTE
• The torque limit cannot work properly when two or more motors are driven by one inverter.
• In the constant power range (Pr.3 Base frequency), the torque limit is activated at the torque less than the stall prevention
operation level, since the magnetic flux decreases.
• When the torque limit is activated during regenerative driving, the output frequency is increased up to the maximum frequency.
• The toque limit is not activated at the frequency of 5 Hz or less during deceleration.
• When using the torque limit under V/F control, note the following points:
- Use the inverter whose capacity is the same as that of the motor.
- The stall prevention operation level (torque limit level) is based on the rating torque of the motor whose capacity is the same
as that of the inverter.
-
When a large value is set in Pr.0 Torque boost, the torque limit may be activated in the low-speed range.
- If more accurate torque limit is required, select Advanced magnetic flux vector control.
 Setting two stall prevention operation levels (Pr.48)
• Turning ON the RT signal enables Pr.48 Second stall prevention operation level.
• To input the RT signal, set "3" in any parameter from Pr.178 to Pr.189 (Input terminal function selection) to assign the
function.
NOTE
• Changing the terminal assignment using Pr.178 to Pr.189 (Input terminal function selection) may affect the other functions.
Set parameters after confirming the function of each terminal.
• The RT signal is the Second function selection signal which also enables other second functions. (Refer to
 Further prevention of a trip (Pr.154)
• Set Pr.154 = "11" when the overvoltage protective function (E.OV[]) is activated during stall prevention operation in an
application with large load inertia. Note that turning OFF the start signal (STF/STR) or varying the frequency command
during stall prevention operation may delay the acceleration/deceleration start.
CAUTION
• Do not set the stall prevention operation current too low.
Doing so will reduce the generated torque.
• Be sure to perform the test operation.
Stall prevention operation during acceleration may extend the acceleration time.
Stall prevention operation during constant-speed operation may cause sudden speed changes.
Stall prevention operation during deceleration may extend the deceleration time.
Parameters referred to
Pr.22 Torque limit levelpage 100
Pr.178 to Pr.184 (Input terminal function
Pr.190 to Pr.196 (Output terminal function
218
10. (H) Protective Function Parameters
10.10 Stall prevention operation
selection)page 283
selection)page 250
page 289).