Variable frequency drives, or commonly known as VFD’s, use pulse width modulation (PWD) techniques to control AC drives. If improper cabling is used in these drives, the high frequency pulses found in VFD can cause destructive motor bearing currents.
The answer to these frequency pulses is many times the uses of variable frequency drive cables between the VFD and motor. These cables are specifically engineered to protect the motors from induced voltage, transient voltage, standing waves, unbalanced electrical fields, noise, reflective current and variable width pulses. The cost of many VFD’s almost always makes purchasing and installing VFD cables to protect that investment a smart and cost effective decision.
There is no industry standard on VFD cables. Many manufacturers will engineer, market and patent their products as VFD cables. You can find a VFD cable in virtually any voltage, shielded and temperature range. Your application and budget should dictate the type of VFD cable you use.
Here are a couple of the most popular constructions of VFD cable:
Corflex VFD Cable – This VFD product is constructed with a continuous corrugated armored sheath and uses 3 conductors and 3 ground wires. The sheath provides a long term low resistance path to ground to protect the drive system. Cable grounds also ensure a balanced, low resistance path to ground to reduce the chance of motor failure due to bearing currents. This is a very versatile and rugged product that can be both used in tray and direct buried however it requires a large installation bending radii due to the armor.
Belden VFD Cable – Belden Wire & Cable makes another version of VFD cable that utilizes a foil/braid shield. This is also a 3 conductor product but only uses one ground wire. The increased strand count, and the fact this product does not have the continuous corrugated armor, makes it a much more flexible option to the Corflex. The 85% braid coverage offer optimum EMI low frequency noise protection, while the 100% aluminum/mylar tape offers RFI high frequency noise protection. Belden’s VFD construction has proven to be very effective on reducing noise and corona discharge. This product can also be used in tray or direct buried.
In terms of cost, the Corflex is the less expensive option typically. However, it is more cumbersome and difficult to install than a product such as the Belden VFD which does not use the armor.
Like previously mentioned, there are dozens of manufacturers who produce and market a VFD cable in some form or fashion. On the market today you will find super flex, robotic, small diameter and low and high temperature versions of VFD cables to only name a few. The goal of each product remains the same: To save or increase the life of the variable frequency drive and motor.
In summary, the days of having to use standard lead wires or tray cables to protect your valuable drives and motors are over. While these VFD cables mean additional upfront cost, their ability to save or extend the life of the drives they are running make good long term business sense for most businesses.