VFD on motor with higher HP

[OperaHouse]

A friend of mine wants to use an AC TECH SM320 which is a 3HP VFD on a 5HP motor that is rated for VFD use. The application uses less than 1.5HP max and does not start under load. I can't think of any real problem. Anything to watch out for before he orders this drive?

 

[ScottyUK]

The oversized motor will have a higher magnetising current which the drive must supply. At this ratio of sizes I doubt there will be a problem, but the drive may be working more-or-less flat out to meet the combined requirements of the 1.5HP load and the higher mag current.



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[Skogsgurra]

At this low load (and if it is a scalar drive) it is possible to reduce motor U/f ratio and that will reduce magnetising current.

If it is a vector drive, the reduction will happen automatically. The reason is that the resulting vector (in most drives) is adapted to real torque need and that mostly also means that magnetising current also is reduced when the load is lower than motor rating.