Posted on 22nd Dec 2022
CM Industry Supply Automation article is the first in a series explaining the crucial elements to consider when sizing a variable frequency drive for a drive system.
The final application will establish the load characteristics, a crucial component that is covered in this article.
Read the other articles in this series on power supply and motor dimensioning.
Making sure a variable frequency drive (VFD) has enough capacity in terms of KW and nominal current rating to enable the motor to generate the required torque throughout the intended speed range while allowing for any periods of overload is probably one of the most crucial aspects of making the right choice.
The various load types can be divided into:
The three typical properties of loads
Continuous torque
The nature of the driven machine, or its application, is taken into consideration as the initial stage in dimensioning a drive system.
Because of their constant torque profiles, HD motors are those that handle loads like augers (drills), screw compressors (for example, chillers), positive displacement pumps, and conveyors.
Adjustable torque
Little initial overload is necessary for motors handling centrifugal pumps and fan applications. They also have a lower initial torque as compared to some HD applications.
Continuous power
Numerous machine tools, such as grinders, lathes, and winders, continuously load motors (CP).
This means that regardless of speed or torque, power remains constant.
A regenerative induction motor is used by an increasing number of devices.
At specified times during operation, built-up inertia in the driven machine may cause the motor to function as a generator and cause the DC bus voltage of the VFD to rise. If this condition is not addressed, the VFD may trip and the load may spin out of control.
Dynamic brake resistors (DBR), which burn surplus regenerative energy as heat, must often be installed in order to use these regenerative applications.
Although it may not always be the most effective technique to manage regenerated energy, this kind of system may have the lowest initial cost.
There are three typical load categories that motors deal with:
Heavy duty and constant torque (HD)
Varying torque and regular duty (ND)
Continuous power (CP)
Every one of these load characteristics might be either continuous or cyclic; cyclic loads can provide unique difficulties for the drive system's overall performance and should be carefully taken into account during the planning stages.
A VFD with an active "front end" can be a more effective option because it will allow regenerative current to flow back into the mains without the need for braking resistors to be connected, which is necessary for applications that may be regenerative.
Do you need specialized assistance?
In a range of industries, CM Industry Supply Automation (Lenze VFD, Lenze Drive, KEB VFD, KEB Drive, Siemens VFD, Siemens Drive, Yaskawa VFD, Yaskawa Drive) supplier and repair service provider assists OEMs in dimensioning and installing cutting-edge, revolutionary variable speed drives.
We offer premium variable speed drives that can help you increase the performance of your application, add automated control features, and improve project energy efficiency.
Contact a variable frequency drive expert today at India: +91 8956113099 Australia: +61 3 9013 5882 or sales@cmindustrysupply.com to find out more about our expert support service.