VFD driven Motors

[shailesh_excl]

I have an engineering spec which says that "VFDs larger than 700 to 2500 KVA shall be powered at 4.16 kV, 3 phase, 3-wire" and
"VFDs 700 KVA or less shall be powered at 480V, 3 phase, 3-wire"

I have a 400 HP cooling tower fan motor ( non-VFD Driven) fed from a medium voltage switchgear. and on the other hand i have a 400 HP ID fan motors (VFD driven) fed from a low voltage switchgear.

Why does inclusion of VFDs in the design allows the ID fan motors to be low voltage. The spec clearly states that motors above 250 HP would be fed from a 4160 switchgear. Any idea..

Thanks

Shailesh

 

[petersonra]

I have an engineering spec which says that "VFDs larger than 700 to 2500 KVA shall be powered at 4.16 kV, 3 phase, 3-wire" and
"VFDs 700 KVA or less shall be powered at 480V, 3 phase, 3-wire"

I have a 400 HP cooling tower fan motor ( non-VFD Driven) fed from a medium voltage switchgear. and on the other hand i have a 400 HP ID fan motors (VFD driven) fed from a low voltage switchgear.

Why does inclusion of VFDs in the design allows the ID fan motors to be low voltage. The spec clearly states that motors above 250 HP would be fed from a 4160 switchgear. Any idea..

Thanks

Shailesh

You seem to have two specs in conflict.

My guess is that one of the primary reasons to operate the larger motors at MV is to reduce the effects of across the line starting that is not present with a VFD so someone allowed a motor > 250Hp to be fed from a LV VFD.