To beanland's (and others) point, LOAD on a motor in a centrifugal fan application is directly related to the air flow. If someone made ANY changes to the mechanical side of the air handler, however seemingly slight, the effects on the motor load are dramatic. As Christoff84 said, the POWER required by the fan is related to the CUBE of the flow change. So if, for example, there was an inlet guide vane being used to regulate air flow BEFORE the VFD was installed, then it was removed BECAUSE someone thought it was no longer necessary now that you have a VFD, the slight restriction of that guide vane just being there may have been limiting the air flow just a little bit. When it was removed, the higher air flow causes a 3 fold increase in motor load. If someone changed a sheave, same issue. So for example in your case with a 135% increase in loading, that could be the result of just a 10% increase in air flow (lot's of assumptions here, I'm just making a point).
Also, the single phase current will always be a little more than 1.732 (the sq. root of 3) times the 3 phase current because ALL of the HP has to be supplied by 2 legs instead of 3 on the INPUT side. So at 120A on the 3 phase side, the single phase current would be 208A at least, plus losses in the VFD. You said 210A, no surprises there.
Hopefully by the way, you used a 60HP Constant Torque rated drive (which would be a 75HP VT rated drive), because if not, the VFD is going to be overloaded. You have to over size a VFD by 2X the motor FLA when using it as a phase converter. Otherwise the diodes on the front end that are doing the conversion to DC are going to be overloaded by that 1.732 factor, and you will not have enough DC bus capacitance to smooth out the additional ripple caused by not having all 3 phases feeding the DC bus. Doubling the VFD rating takes care of both issues.[/QUOTE
I personally have no experience with this brand of grain dryer, my customer told me that this particular dryer came from the factory with "Too much restriction" on the airflow....So now that you say that i wonder if he didnt make some alterations of his own??? As far as the drive goes, Ive always ordered drives double the HP rating for scenarios like this. This is my first time installing a schneider brand VFD, so I gave my sales rep at my supplier my motor ratings and he told me i didnt need to double the size with this particular drive...hes always been a knowledgable guy so i didnt argue with him. So do you think that too much airflow could be my problem?