This Tech Tip is a brief overview of some of the benefits of using a choke with Variable Speed Drives (VSDs)

Input chokes can be used to reduce the supply line harmonic currents and voltage distortion generated by almost all inverter drives on the market today.

Here are some of its benefits:

• Reduce power supply harmonic currents
• Reduce the overall input current to the drive
• Provide additional protection against mains borne voltage spikes

The use of line chokes is recommended under the following circumstances:

• Close connection of several drives in parallel
• Line supply with significant disturbance from other equipment (interference, overvoltages)
• Line supply with voltage imbalance between phases above 1.8% of the nominal voltage
• Drive power supplied by a line with very low impedance (in the vicinity of power transformers 10 times more powerful than the drive rating)
  Installation of a large number of frequency inverters on the same line
• Reduction of overloads on the "cos phi" correction capacitors, if the installation includes a power factor correction unit.
• Where the local mains supply quality may be poor or unknown
• Where high current switching loads such as large DC drives or soft starts are operating
• In remote areas prone to lightning strikes

NB: Chokes should be installed upstream of the drive.