Has anyone ever heard of using a 480 volt 3 phase drive with a 230 volt 3 phase motor and changing the volts/hertz ratio to overcome a high starting torque? I would appreciate anyone's help on the subject.
Many VFD's offer a "low frequency boost" to provide more torque at low speeds to get the motor moving. How much depends on the manufacturer and the drive. You do not need to go to a higher voltage rated drive to get this. Also some offer a "jump to speed" function that applies the chosen frequency ( presumably with boost ) to the motor without ramping it up over a time from zero. Both these options help to start a load that has high starting torque. If you are having difficulty with starting torque, the more usual approach would be to go to a larger HP drive at the same voltage rather than a higher voltage drive. The other question is how long do you need this high starting torque? Just for a second or two to get it moving, or for 20 seconds to get the load accelerated up to speed?
Your best bet is to obtain a complete description of the starting requirements ( and running ones ) and talk to various manufacturers for their recommendations. In the starting requirements you need to include among other things the breakaway torque and the accelerating time and the number of times per hour that you will have to do this. You also need to include the motor characteristics and if you are willing to change the motor to get better performance. Some motors have higher starting torque than others and changing the motor may actually reduce the requirements on the drive.
> As with the answer in the last thread, there is no need to go to a 480V drive to increase your starting torque. The voltage boost settings as previously suggested may work for you if you are operating the drive in a standard volts per hertz control mode. I would suggest, if it is available on your drive, to program the drive to run in an open loop (sensorless) vector control mode. This control method will greatly improve the starting torque capabilities of your motor/drive system and should allow you to achieve starting torques in line with starting the motor across-the-line.
Motors of the same horspower can be had in different nema design ratings. Nema design B is standard. Design C has a higher starting torque and design D is for starting high inertia loads. If you can't swap the motor but you can change the gearing or pulleys then a higher ratio will give you a lot more starting torque. This works because the drive can run the motor at higher speeds (up to 90 or 120 HZ depending on motor balance.) Swapping the drive for a larger size works since more starting current is availible. I've never heard of running a 230V motor on a 440V drive except at very high speeds.
