How can I tell if a cable is rated for use as motor leads with a variable frequency drive?

Question

I understand that the switching edges generated by a VFD can cause corona breakdown of the insulation on the motor leads. Due to this, it is recommended that some cables be used for VFD motor leads, and that others not be used. How can I tell? I am particularly interested in Lapp ÖLFLEX® CLASSIC 110 CY.

https://products.lappgroup.com/online-catalogue/power-and-control-cables/various-applications/pvc-outer-sheath-and-numbered-cores/oelflex-classic-110-cy.html

Answer 1

You will probably need to follow specific recommendations published by VFD manufacturers. Also consider mitigation that might be available from the drive manufacturer built-in or added at the drive output. Detailed recommendations should be available from the large VFD manufacturers such as ABB, Rockwell / Allen Bradley, Yaskawa, Siemens, Eaton / Cutler-Hammer, Schneder / Square D / Télémécanique, and General Electric.

Gary Skibinski of Allen Bradley and John Bentley of ABB have written papers on the subject;

E. J. Bulington, S. Abney and G. L. Skibinski, "Cable alternatives for PWM AC drive applications," Industry Applications Society 46th Annual Petroleum and Chemical Technical Conference (Cat.No. 99CH37000), San Diego, CA, 1999, pp. 247-259. doi: 10.1109/PCICON.1999.806443

J. M. Bentley and P. J. Link, "Evaluation of motor power cables for PWM AC drives," in IEEE Transactions on Industry Applications, vol. 33, no. 2, pp. 342-358, Mar/Apr 1997. doi: 10.1109/28.567793

Answer 2

That cable is not something I would recommend. Yes, it is shielded (screened) and that's important, but the individual conductors are insulated with PVC, and that's where the problem lies. PVC insulation is applied to the copper wire as a liquid and therefore has microscopic bubbles in it. Those bubbles weaken the insulation's ability to withstand the corona discharge that can take place as a result of the high speed transistor switching.

What you want to look for is referred to as "VFD cable" by most mfrs, including Olflex. The individual phase conductors will be XLPE (Cross Linked Poly Ethylene) insulation, whuich is formed around the copper wire as a heat shrink process. There is a PVC jacket (which is OK for the jacket), and a more robust shield/screen system and drain wire.