Altivar 630 starting torque

[MikiBg]

Hi all!
I'm currently dealing with Altivar 630 VFD and wondering how to find out starting motor torque, because no such parameter is available.
Is it implicitly determined by low (starting) frequency and V/f ratio, regardless of control mode selected? Is it related to acceleration time and current limit, or motor is always started with rated or maximum torque?

 

[jraef]

"Starting" torque is a concept that is based on Across-The-Line (DOL) starting of an AC motor, based on the reaction of the motor to the initial high slip and high starting current due to low power factor when it is stopped. It does not apply to VFDs or motors controlled by VFDs because the entire process of accelerating the motor is fully controlled by the drive from the outset.

A VFD just creates torque in the motor, the basis of which is thought of as "Constant Torque" meaning full motor torque at any speed. How much EXTRA torque they can create in the motor is typically a function of the control method: any kind of Vector Control can usually make the motor produce Break Down Torque at any speed, which is HIGHER than "Starting" or Locked Rotor torque, but only for about 2-3 seconds. Any Constant Torque (CT) rated drive, Vector or not, can make the motor deliver 150% torque for up to 60 seconds, which is very close to the typical starting torque that a basic Design B motor will produce. With CT rated drives, 60 seconds at that 150% level is a lot longer than a DOL motor would be delivering starting torque, so you often find that heavy loads will actually accelerate faster when driven by a VFD than if started DOL.

Non-Vector (simpler V/Hz control method) drives lose that high torque capability at low speeds but now are often only associated with "Variable Torque" (VT) rated drives, so the overload capacity of the drive will be lower, typically 110% for 10 seconds. A VT rated drive will not allow that peak performance, but that is a feature not needed in a load that would be associated with that "VT rated" drive sizing.


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