Multiple vfd loads in one conduit

[koelsche]

Have an installation of five motors in one embedded PVC conduit. 5hp each. All are on AB Drives. They run fine until run at low HZ around 4hz then trip out on over voltage load side. Run with single THHN conductors with filters on load side. No problems if drop carrier frequency to 2kHZ but motor noise is too much. The noise is especially bad on higher rpm motors. Can I adjust carrier freq. on the just the slow run mtrs or do I need to tune all the same? I know install is not ideal but a lot of cash to change so trying to make it work.

 

[Jraef]

Have an installation of five motors in one embedded PVC conduit. 5hp each. All are on AB Drives. They run fine until run at low HZ around 4hz then trip out on over voltage load side. Run with single THHN conductors with filters on load side. No problems if drop carrier frequency to 2kHZ but motor noise is too much. The noise is especially bad on higher rpm motors. Can I adjust carrier freq. on the just the slow run mtrs or do I need to tune all the same? I know install is not ideal but a lot of cash to change so trying to make it work.

You are getting inductive coupling on the motor leads and even if the VFDs are not tripping out, you are likely doing damage to the motor insulation as well. This should never have been done this way, sorry.

But one possible solution that would cost a lot less than ripping out conduits might be to use Sielded VFD lead cable. People like Bellden and Lapp make and sell that now. It's not cheap but it is a good idea to use it anyway, and in this case it may be your only viable solution.