Why Do VFD Motors Fail Repeatedly in Field

Variable frequency motor systems and frequency drive motor setups are widely used in industrial automation to control speed and torque for pumps, conveyors, fans, and more. However, some operators have raised questions about why certain VFD motors and drives fail repeatedly in the field, even when they are supposedly well-installed and configured. This concern is especially common among maintenance technicians and plant engineers who expect reliable operation but encounter repeated faults or unexpected downtime.

In many online discussions and technical forums, users point out a range of possible causes that contribute to repeated motor and drive issues.

What Do Users Report?

Some automation professionals mention that their variable frequency motor installations seem to fail too often despite proper wiring and grounding. In certain threads, multiple motors and associated frequency drive motor units in the same location failed in a short time, suggesting installation or environmental factors rather than single equipment defects. This has sparked deeper discussion around installation quality, motor selection, and system compatibility as core concerns.

Key Factors Behind Repeated VFD Motor Failures

1. Incorrect Motor or Drive Match

Selecting the right motor for VFD operation is critical. A frequency drive motor needs to be inverter-rated if it is to withstand the peculiar electrical stresses introduced by the drive’s switching patterns. When a motor not designed for VFD use is operated under a variable frequency motor drive, it can degrade prematurely due to electrical or thermal stress.

2. Bearing Currents and Electrical Discharges

One lesser-known but significant cause of bearing damage involves common-mode voltage. Variable frequency drives switch power at high-frequency pulses to generate adjustable output voltage and frequency. These pulses can create unwanted shaft currents that flow through motor bearings. Over time, this results in microscopic pits on the bearing surface, escalating into bearing failure, noise and vibration issues.

These effects can be especially pronounced if the grounding and shielding practices around both the motor and the frequency drive motor control are not properly implemented.

3. Low-Speed Overheating

When motors run at low speeds (for example, under 20–30 Hz), cooling becomes more difficult because the shaft-mounted fan spins slower. This reduces heat dissipation right when the drive and motor are working hard to maintain torque at reduced speeds. Over time, this heat buildup can accelerate insulation breakdown and wear on motor components.

4. Improper Installation or Wiring Practices

Even high-quality variable frequency motor and frequency drive motor products can underperform if installation standards are weak. Improper cable routing, inadequate shielding, loose connections, and poor grounding all contribute to electrical noise, interference, and premature component failure. Regular installation checks and cable assessments can help reduce these risks.

Practical Measures to Improve Reliability

• Routine Inspection and Parameter Review

A frequent recommendation in user discussions is to verify motor and VFD parameters such as voltage, current limits, acceleration/deceleration ramps, and cooling settings. Incorrect parameters can cause nuisance faults or accelerate wear. Regular reviews of these settings can improve motor performance and reduce alarms.

• Grounding and Shielding Enhancements

Ensuring that motor cables are correctly shielded and grounded reduces noise and current loops that contribute to bearing currents and electrical interference. This includes using VFD-rated cables and checking ground integrity at both ends of the frequency drive motor system.

• Monitor Operating Conditions

Consistent monitoring of motor temperatures, current trends, and vibration levels gives early warning signs of excessive wear or issues. Implementing predictive maintenance based on operational data can prevent unexpected failure events before they occur.

Repeated failure of variable frequency motor systems and frequency drive motor units is rarely due to a single factor. It often involves a combination of motor selection, installation quality, operating conditions, and environmental influences. By understanding these key contributors, you can better diagnose issues and take proactive steps to build more reliable automation systems.

Zhejiang Ligong Motor Co., Ltd. encourages operators to pay special attention to proper motor matching, installation quality, and maintenance practices to maximize system lifespan and performance.