What are the consequences of running a 40HP motor, with a 50HP Drive, instead of the 40HP Drive ? This is for a variable torque application.

You shouldn't have any problems. Just be sure to enter the motor data for the 40HP motor.

Bernardo, You will have no issues using an oversized VFD. I am assuming you are using a voltage source drive (most common topology). This design manages the voltage and frequency to attain commanded speed. The current supplied to motor is only what is needed to magnetize the windings plus the torque producing current. In other words, the VFD is a 'current allower' and not a 'current pump'.

The key to your application is to properly program the drive to protect this motor which is the MOL or motor overload protection parameter in all drives. Good luck.

Other than your wallet being lighter, depending on the application it might be in your benefit. Depending on the machine frame size your losses may actually be less than the 40 HP. But as noted, make sure you have your protection and motor parameters set correctly or you could cook your motor.

Only problem you might see if the HP variance is too great is possibly your current measurement resolution may not be good as the scaling on the sensor may be too coarse for a small motor. 40-50 probably not, but if you tried it with a 150, you may not be able to draw enough current to register on the larger machine accurately.

I agree. When setting up any VFD application use the motor nameplate data to provide an accurate look at what is happening with the load and providing suitable motor circuit protection. Drives are a current delivering device and are marked by horsepower for convenience only. Application, load, environment, derating for temperature, altitude or even stopping/braking may require additional capacity.

Just to expand the answer a little. The motor data is not just amps but the electrical properties of the motor, motor constants. The VFD should have parameters where you let the VFD know the size of the motor, number of poles and nameplate voltage. The VFD will probably have a stored set of motor constants for each that it will load to get close to optimum efficiency.

If you have a 50 hp drive running a 5 hp motor there may be some filtering issues but a 40 hp is no problem.

Ok, thank you all for your great responses, the thing is that we have a project for a customer and we had assigned 40HP Drives to 40HP motors, but the supplier could not deliver this drives, so I proposed to change them to 50HP Drives, the size is the same and all, and it has been done before without any problems, but I just wanted to expand my knowledge about doing this. Thanks again

it will last years longer

I often buy a brand of drive that offers a "heavy duty" version of each drive size. When I buy a 40 HP HD drive it is actually just a 50 HP drive marked as a 40-HD. We do this all the time and have never had a problem as long as you are not more than 50% below the intended capacity. Below 50% of rated capacity you start to see conducted noise issues because you are not drawing enough current for the magnetics to work well and control precision issues that likely stem from measurement resolution issues mentioned previously, more...

With a higher HP rating drive, one thing you can do is to set the PWM frequency higher so that the audio noise is lower.

there is no problem of that, but you should program the maximum current and over load parameter to protect the motor from burn .

There will no no problem. make sure use the EOL is set for the motor data.

Make sure motor is Inverter rated and watch your cable lenght.

IGBT's can effect motors with long cable lenght

Use V/Hz setting in drive

As already said, strong oversizing affects current measurement resolution, but this could be actually an issue only in vector control (especially sensorless).

The vsd can accept a range of horse powers , for instance a50hp vsd can may be accept motors from 30hp to 50hp if you carry out AMA.its aplus to use a slightly higher vsd hp than the motor because you increase its life span.

You have to ensure that required parameters like acceleration time,over current,voltage,frequency are entered as per your equipment requirement.