Efficiency Calculation For A VFD Drive

Change (reduce) the fan pitch to get greater motor speed!

(To all the others, this answer relates to our long gone VERY serious discussion on bathtub breaking.)

I know that many of you will just ignore this request for assistance,while others will direct him to ask the manufacturer, while others will suggest alternate gearing and such.

Please give him all your BEST help!! He really needs it.

It might be easier to trim the fan diameter.

Some of those numbers seem rather strange. For instance, on a 690 V motor, the amps would not likely equal the KW.

I liked your response, since you laid it all out there. I was mistaken with my rules of thumb estimate.

Basic "Afinity law of speed" for a centrifugal (quadratic) machine states that the power required by the load from the motor changes at the cube (3rd power) of the speed change.

All other factors will remain relatively constant, only the speed changes so you are increasing the speed by 5%, your power will likely increase to being 1.05³

Hire an appropriate ''outside'' (specialist/consultant) to assume liability if their recommended ''fix'' doesn't fix it...

The motor nameplate mentions 990 rpm, but something appears mistaken about amp draw, with a power of 730 kW, and 690 V service, I see no way to draw 730 A, but only slightly more than 610 A for three phase service. I have no idea if your VFD can be pushed higher, and apparently you may be asking more of the motor than it deliver without leaking smoke.

Beyond Mr. Niazi's excellent response, if your air temperature changes with the increased air flow, you may end up with a different load.

In paper mills, we will at times push the equipment to the design limit, which is usually temperature rise of the motor stator, all other components suitably sized. If you run the fan at such a speed to hit your 730A motor nameplate current reading, amperes of the 3 phases balanced to design specs that Compton-Greaves can supply you, assuming that your stator cooling systems are not fouled and that your ambient temperature falls below the rated (maybe 40C), then you will hit your production limit, and allow for normal equipment design life.

Auxiliary cooling, or very low ambient temperature, can allow higher loads, which then shifts the stress away from the motor winding temperature, and on to mechanical components, bearings, couplings, etc.