Electric Motor Bearing Failure and Use of the Proper VFD Cable

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Electric Motor Bearing Failure and Use of the Proper VFD Cable

What causes bearing failure to occur between the variable frequency drives (VFD) and electric motors?  What can be done to minimize the potential for failure?

ball bearing

For starters, the ball bearing is the connection between the shaft and the motor frame.  There are two rings: an inner ring (which is in contact with the shaft) and an outer ring (which is in contact with the motor frame).  The shaft turns due to electromagnetic interaction between inductors on the shaft and inductors on the frame. When the shaft turns, it drives the machine.

The problem lies in the connection between the VFD and the motor.  The VFD send power to the motor and some signal contents reflect off the motor and move back towards the VFD.  The reflected waves collide with the upcoming waves and this causes high voltage spikes.  The high voltage spikes cause strong electric fields which then influence the motor.

The voltage spikes and strong electric field then produce a high frequency flux around the stator.  If this frequency flux becomes high enough to overcome the impedance of the bearings’ oil film, a current starts to flow.  The end result is spark erosion.  Tiny metal particles of steel balls and rings melt and the bearing eventually fails.

LUTZE Driveflex VFD XLPE A216

However, LUTZE has come up with the perfect solution and that is to minimize the electric field.  A symmetrical construction results in a smaller electric field. The DRIVEFLEX® A220 is the most capable solution thus far of preventing bearing currents.  It connects all three earth wires and connects the cable shield to PE on both cable sides.

So, there you have it! LUTZE has created the solution to your bearing current problems with the DRIVEFLEX® A220.

LUTZE presented this information in an educational session at our recent Product and Technology Expo.  Check out the full presentation here.

Are you interested in learning more about this VFD cable solution?  Contact your French Gerleman Account Manager or contact us.

 


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VFD Cables VS. Traditional Cables for Drive Applications

Variable Frequency Drive (VFD) cables have been around since the early 1990s in order to help minimize operational issues with VFD systems. The advancements in Insulated Gate Bipolar Transistors and technology drives caused a significant increase in the high frequency information output from the drive inverters. That means that traditional power cables had issues handling these high frequency signals, which could lead to system problems.

This is why VFD cables are so important. They provide extra protection and are specifically designed for installation between a motor and a VFD. This reduces any downtime when using THHN or shielded tray cables. VFD cables are designed for higher stranding, robust insulation and overall better shielding.

Why should you choose VFD cables?

VFD cables are more reliable than traditional cables, and offer better protection and improved performance over traditional. Traditional cables cannot compare to the performance improvement and they lack a shielding system, which minimizes radiated and conducted noise. VFD cables offer industrial grade XLPE insulation, which is entirely more reliable than traditional.

Product Spotlight:

General Cable offers a wide range of VFD cables perfect for any setup. With the CVTC® and CCW® lines, General Cable offers the highest quality VFD cable solutions for many categories including factory automation, traditional power generation, marine, refining and petrochemical, specialty chemical and wastewater treatment applications. General Cable designs incorporate symmetrical grounding which minimizes ground voltages and induced ground currents that can lead to motor-bearing fluting and premature motor failure. VFD cables from General Cables undergo rigorous testing to ensure the most reliable power from the AC drive to AC motors. You can rest easy knowing your cables are performing at their best.

CVTC

CVTC® VFD
CVTC® VFD cables are designed and engineered to handle the challenges presented in VFD environments. They are used in a wide range of applications. CVTC is a low voltage power, shielded 600V, UL type TC-ER, unarmored and Method 4 color code.

Features (SPEC 4550):

  • Rated at 90°C wet or dry
  • Combination foil/brand shield provides maximum shield coverage required for VFD applications
  • Abrasion and chemical resistant
  • Stable electrical properties over a broad temperature range
  • Sunlight and weather resistant
  • Meets cold bend test at -25°C
  • Flexible strand conductors for all sizes to allow for ease of installation and long-term performance in light duty flexing applications

Applications include:

  • Free air, raceways or direct burial.
  • For use with AC motors controlled by pulse-width modulated inverter in VFD applications rated up to 1000V.
  • For use in aerial, conduit, open tray and underground duct/installations.
  • It is permitted for use in Class 1, Division 2 industrial hazardous locations per NEC.
  • Permitted for Exposed Run use in accordance with NEC.

CCW

CCW® VFD Low and Medium Voltage Power

General Cable’s CCW® Armored Power, 3/C VFD and 4/C cables are insulated conductors and grounding wires that are cabled together with non-hygroscopic fillers.

Features (SPEC 9600):

  • 3-conductor CCW power cables with three grounding wires are recommended for use with pulse-width AC drives.
  • CCW armor provides an impervious barrier to moisture, gas and liquids.
  • CCW armor provides EMI shielding performance.
  • Factory assembled and tested cable for use as an alternative to cable in conduit wiring systems.
  • Meets cold impact at -40°C.
  • 90°C continuous operating temperature, wet or dry.
  • 130°C emergency rating.
  • 250°C short circuit rating

Applications include:

  • 3-conductor CCW armored cables with 2 symmetrical grounding wires are the preferred wiring method for use with AC motors controlled by pulse-width modulated inverters in VFD applications.
  • CCW armored cabled offer an economical, rugged and reliable alternative to labor-intensive cable in conduit wiring methods.
  • For use in Class I, II and III, Divisions 1 and 2; and Class I, Zones 1 and 2 hazardous locations per NEC Articles 501, 503 and 505.
  • For use as services, feeders and branch circuits for power, lighting, control, and signal circuits in accordance with NEC articles 330 and 725.
  • Installed indoors or outdoors, wet or dry, buried, embedded, in a raceway, as aerial cable on a messenger, in cable trays, or as exposed runs secured to supports in accordance with NEC article 330.
  • Recognized for use on fixed or floating offshore petroleum facilities as recommended by the American Petroleum Institute.

Want to learn more about VFD cables? Give your French Gerleman Account Manager a call today or contact us.