Why screened cables for vfd

If your drive is already mounted, the only practical option is to install a filter at the drive to limit the rise time of the voltage.

The fast rise times of the output voltage that are applied to the cable result in transmission line reflections that can essentially double the voltage for short durations when the output switches. These spikes can exceed the corona inception voltage of the cable insulation. If air is present, ozone will be produced. Ozone will degrade PVC and can lead to a cable failure. Motor insulation can also be damaged by these high voltage spikes. While XPLE cables have a lower capacitance, which can influence transmission line effects, if you have a motor with insulation failures, you will probably need a filter at the drive or a terminator at the motor.

It is worth noting that most new motors that are inverter rated have improved insulation that essentially eliminates insulation failure due to these voltage spikes. Bearing currents can result in pitting of the bearing race and over time, failure of the bearing.

There are many pictures of this phenomena, called fluting, available online. Over the years, I have experienced more issues with bearing currents than motor insulation failures. A large portion of bearing current is caused by transient common-mode voltages generated by the switching of the drive output devices. The key to minimizing these voltages is to keep the ground potential at the drive at the same ground potential at the motors. In other words, keep the impedance of the ground system as low as possible.

Electromagnetic interference EMI usually affects the environment more than the cable. Affixing the shield to one of the PE terminals will continue the protection.

In essence, you create a Farrady Cage to keep the noise contained and safely removed to earth ground. Hello I am looking for VFD cable for my small project. I was looking all over the KW area. You must be logged in to post a comment. This site uses Akismet to reduce spam. Non-VFD cable also allows common-mode or stray voltage to find its way through the VFD motor and equipment grounds, which causes motor and equipment failure.

VFD cable significantly reduces the risk associated with these issues. Images courtesy of CJ Cowie. These systems are commonly found where motors are being used to control a process or equipment requiring varying motor speeds i. Smaller-sized VFD controllers are even more susceptible to charging currents.

In this case, the charging current associated with a higher cable capacitance may damage the drive output. Again, installing a lower capacitance VFD cable reduces this risk.