variable speed drives
Torque & special uses
The curves opposite define the available continuous torque and transient overtorque for both force-cooled and self-cooled motors. The only difference is in the ability of the motor to provide a high continuous torque at less than half the nominal speed. 1 Self-cooled motor: continuous useful torque
2 Force-cooled motor: continuous useful torque 3 Transient overtorque for 60 s 4 Transient overtorque for 2 s 5 Torque in overspeed at constant power
Use with a motor with a different power rating to that of the drive The device can power any motor which has a lower rating than that for which the drive was designed. For motor ratings slightly higher than that of the drive, check that the current taken does not exceed the continuous output current of the drive. Testing on a low power motor or without a motor In a testing or maintenance environment the drive can be checked without having to switch to a motor with the same rating as the drive (particularly useful in the case of high power drives). This use requires deactivation of motor phase loss detection. Use of motors in parallel The device can power any motor which has a lower rating than that for which the drive was designed. For motor ratings slightly higher than that of the drive, check that the current taken does not exceed the continuous output current of the drive. Motor switching at the drive output Switching can be carried out with the drive locked or unlocked. In the case of switching on-the-fly (drive unlocked), the motor is controlled and accelerated until it reaches the reference speed smoothly following the acceleration ramp. This use requires configuration of automatic catching a spinning load ("catch on the fly") and activation of the function which manages the presence of an output contactor. Note: Depending on the drive rating, downstream ferrite suppressors may be required between the drive and the output contactor (see page 51). Typical applications: loss of safety circuit at drive output, bypass function, switching of motors connected in parallel. Recommendations for use: synchronize control of the output contactor with that of a freewheel stop request from the drive on a logic input.
(1) For power ratings y 250 W, less derating is required (20% instead of 50% at very low frequencies). (2) The nominal motor frequency and the maximum output frequency can be adjusted from 40 to 500 Hz. The mechanical overspeed specifications of the selected motor must be checked with the manufacturer.
Example of loss of output contactor
N t1 > 500 ms KM1 0 1 t2 t
KM1: contactor t1: KM1 opening time (motor freewheeling) t2: acceleration with ramp N: speed
Altivar 312 T/Tn 1,7 1,75 1,50 1,25 2,25 1 2 0,95 0,75 0,50 0,25 0 25/30 50/60 75/90 100/120
1 2 4 3
Available continuous torque and transient overtorquePrevious Page