Variable Frequency Drives

Variable frequency drives (also called "VFDs," "AC vector drives," "inverters" or "variable speed drives") can be thought of as a motor controller that operates the motor by changing the applied voltage and frequency to the motor. A VFD can control the speed of a motor, as well as how it starts and stops. One advantage of using a VFD is it limits the inrush (starting) current, which is easier on the motor.

According to Electrical Construction and Maintenance Magazine, variable frequency drives  are "the most effective motor controller in the industry today."

Motor Operation

Motors can operate in one of two ways. The first is with direct line starting where the motor is connected directly to the AC line supply of the motor terminals. With this type of connection there is a high in rush (starting) current. This high in rush limits the number of times you can start/stop a motor. The direct line connection also means that there is no speed control.

The second method is with a variable frequency drive, also called a VFD or AC Vector Drive, which can be thought of as a motor controller. The VFD controls the motor by changing the applied voltage and frequency to the motor. With this method the in rush current is also limited, which is much easier on the motor. With the use of a drive you can control the speed of the motor as well as how it starts and stops.


Because VFDs offer additional motor control:

  • They allow speed and directional control of industrial equipment and processes.
  • They can be programmed precisely to meet load demands and application requirements.

Reducing motor speed can result in a lower required operating power, which can reduce cost. VFDs also help to extend the life of industrial equipment, since smooth acceleration and deceleration results in less shock and less material wear.

Variable Frequency Drive Applications

VFDs are used in a number of industrial applications, including:

  • Material handling and conveying
  • Mixing and blending
  • Pumping
  • Air handling (fans)
  • Automation equipment
  • Packaging equipment
  • Processing equipment
  • and many more

NORD Drivesystems Manufactures Efficient Variable Frequency Drives

NORD Drivesystems offers four styles of motor controllers; three variable frequency drives, and one soft starter:

SK500E Variable Frequency Drive

The SK500E is a panel mount drive (installed in an electrical cabinet), which is the most common way variable frequency drives are housed.


 NORD SK200E Variable Frequency Drive 


SK180E Variable Frequency Drive 


SK135E Variable Frequency Drive


The SK200E, SK180E and SK135E are decentralized controls. These motor controllers are not installed in an electrical cabinet, but rather directly mounted to the motor or nearby. There are only a few manufacturers in the world that offer products like this.

Decentralized controls offer many advantages:

  • Since the VFD doesn't have to be mounted in an electrical cabinet, you can have a smaller cabinet, thereby reducing the cabinet cost.
  • VFDs generate heat. This means that if they are mounted within a cabinet, the heat has to be addressed in some way. Mounting the motor controller on or near the motor in an open environment allows for better cooling.
  • Mounting the VFD directly to the motor eliminates having to run individual power cables back to the central cabinet, which is another cost savings.
  • Decentralized motor controls decrease installation time and keep labor costs to a minimum.
  • Distributed systems allow for inexpensive system modifications and upgrades as needs arise.


Connect with a NORD Drivesystems representative today to discuss how a variable frequency drive could optimize your material processing and output.



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