When it comes to motor and drive, the AC drive must be of equal in size to the motor or greater. If your application needs high starting torque because of the nature of the load, the drive should be oversized to match it. This is why it is critical to know the specific characteristics of the load to correctly match the size of the drive. You can think of the simplest example of a fan. Though it needs low starting torque, yet, it needs higher power once it runs at full speed.
What this means is that it would only be acceptable to have an AC drive smaller than the motor when the latter is not expected to operate at or over its starting speed. Despite this, you still have to know the up times of the operation or load requirement and its starting torque. Moreover, keep in mind that drives are chosen based on electric current and not the power. For instance, some pumps need higher current than regular AC motor power for the same power. Hence, when the nominal current, which is related to torque, comes lower than 50%, selecting the drive would be in a different manner.
Take for example the case with conveyors used during mining. They run in miles and need more than 30% of total voltage to start working. The case of a fan is different because while it needs higher starting torque to accommodate inertia, the torque decreases when the fan is now running at a lower speed than it takes to start it. Thus, it is the particular nature and characteristics of the load that has to be considered when sizing an AC drive for your application. If you are still confused with those elements involved in drive selection, just give us a call. We would be glad to assist you on this matter and help you end up with the right AC drive.
Comments