How To Troubleshoot Electric Motor Fluting

We rely on electric motors to power our machinery, but they are prone to various problems. One of these is electric motor fluting, particularly prevalent in large motors or when using Variable Frequency Drives.

Fluting is accompanied by excessive heat, noise, and vibration, and is a sign that bearing failure, and ultimately motor failure, is near. Early detection of this common problem is crucial to ensure your equipment’s efficient operation and longevity.

But what exactly causes electric fluting to occur, and what are the danger signs to watch for? Read on to discover how to troubleshoot electric motor fluting.

What Is Electric Motor Fluting?

When voltage accumulates on a motor shaft, it can find the path of least resistance to the ground via a motor’s bearings. When that current passes through the bearing instead of a grounded source, it leads to a type of electrical erosion called electric fluting.

The electrical discharge erodes metal surfaces, creating a series of ridges (“flutes”). These flutes appear along the bearing raceways — the circular groove on the outside of the inner ring, and the inside surface of the outer ring. This can lead to major malfunctions of the bearings and consequently of the motor.

Electric fluting is common in motors equipped with variable frequency drives (VFDs).

What Are The Signs of Fluting?

You can detect fluting issues by watching out for these signs:

• Washboard-like ridges (flutes) will appear along bearing raceways.

• Bearings, raceways, or rollers may have an irregular sheen.

• The metal may suffer pits, cracks, and discolorations.

• The motor may make loud, unexplained noises. By the time this happens, the damage may already be severe.

Any or all of these can indicate electric motor fluting. However, loud noise itself, in the absence of other signs, could be a sign of other problems. If unsure about the cause of the noise you’re hearing, examine the bearing for signs of physical damage.

Preventing & Troubleshooting Motor Fluting

Here are some tips for troubleshooting and preventing electric motor fluting.

Is the Motor VFD Rated or Not?

Electric motor fluting typically occurs due to an electrical current induced on the shaft of a VFD. But the VFD itself is not to blame. The common cause for this is that the motor is not properly VFD-rated.

And if that motor is larger, the higher magnitude of the circulating current is more likely to cause fluting. So, if you’re using a VFD, you should use VFD-rated (also called inverter-rated) motors.

Using VFD Rated Motors

Always use the correct industrial components. VFD-rated motors, otherwise known as inverter-rated motors, are specifically designed to work with VFDs. They can handle the potential voltage spikes and are therefore the best way to prevent electric motor fluting when using a VFD.

Build-Up of Current?

A build-up of current has to go somewhere and, on its way to the ground, may pass through the bearing. This can cause catastrophic damage if left to continue. Fortunately, there are ways to protect your motor and deflect the current.

Redirect the Current With Brushes on the Shaft

To correct the problem of electric motor fluting, you must redirect the stray current that is causing all the damage.

• For machines rated at under 100 horsepower, attach a carbon fiber brush to a shaft grounding ring on the drive side of the shaft. It will redirect the current to ground. This allows electricity to bypass the motor’s bearings and find its way to ground.

• In machines rated at 100 horsepower and over, attach a non-conductive ceramic bearing to the opposite side of the shaft, as well as the carbon fiber brush mentioned above. Electricity can’t pass through the ceramic bearing, thus safely redirecting the current away.

Absorb Stray Current With Nanocrystalline Technology

Voltage build-up in motors will always seek the path of least resistance – the bearings.  This problem is compounded when using Variable Frequency Drives.

Although VFDs offer great benefits like optimizing energy consumption, their high switching frequencies can cause an electrical build-up. Nanocrystalline technology addresses the problem by treating the underlying cause. It absorbs stray currents while protecting the motor from damage.

Conclusion

Electric motor fluting can cause bearing failure, and later motor failure if left untreated. It’s especially common when using a VFD without a VFD-rated motor. Although there are signs to watch for, such as excessive noise, this is usually a sign that the damage is already done.

There are several ways to address electric motor fluting, but the most sensible approach is to prevent it from happening in the first place. Only use genuine parts, and ensure that machinery using VFDs has the best VFD-rated motors.

At AEC, you’ll find a wide range of motors, VFDs, and components to keep your machinery running in optimal condition. Contact us today to get the right parts for your specific needs.