cmindustrysupply cmindustrysupply

Leading Industrial Automation Solution Provider

Servo Drive & Motor Expert | VFD AC Drive Repair

Posted on 28th Nov 2023

Top Motor Issues for VFDs

KEB F5 Drive

Variable Frequency Drives (VFDs) are commonly used to control the speed and torque of electric motors. While VFDs offer many advantages, they can also introduce certain issues related to the motor they control. CM Industry Supply Automation - KEB F5 Drive & Lenze Drive supplier share five top motor issues associated with VFDs:

Voltage Spikes and Transients:

Issue: VFDs can generate voltage spikes and transients that may damage the motor insulation.

Mitigation: Install a line reactor or an isolation transformer to reduce voltage spikes. Consider using surge protection devices to safeguard the motor against transient voltage.

Insulation Breakdown:

Issue: The fast switching of VFDs can stress the insulation of motor windings, leading to premature insulation breakdown.

Mitigation: Use a motor with insulation designed for VFD applications. Implement proper grounding practices and consider adding additional insulation to mitigate the effects of voltage stress.

Bearing Currents:

Issue: VFDs can induce circulating currents in the motor shaft, leading to bearing damage.

Mitigation: Install insulated bearings or shaft grounding devices to provide a low-resistance path for circulating currents. Implement common-mode chokes or filters to reduce common-mode currents.


Issue: Continuous operation at low speeds or frequent starts and stops can lead to motor overheating.

Mitigation: Ensure that the motor is adequately sized for the application. Implement cooling solutions such as external fans or blowers if needed. Monitor motor temperature and use VFD parameters to set limits for thermal protection.


Issue: VFDs can introduce harmonic distortion into the power system, affecting motor performance and efficiency.

Mitigation: Use line reactors or harmonic filters to mitigate harmonic distortion. Choose VFDs with built-in harmonic reduction features. Consider power quality analysis to assess and address harmonic issues in the system.

It's crucial to note that these issues are not inherent flaws of VFDs but rather challenges that need to be addressed to ensure the reliable and efficient operation of motor-driven systems. Proper installation, appropriate motor selection, and adherence to best practices for VFD application can significantly mitigate these issues.

Regular maintenance and monitoring of motor parameters, along with a comprehensive understanding of the motor-VFD system, are essential for identifying and addressing these issues before they lead to motor failure or reduced performance. Consulting with motor and VFD manufacturers such as CM Industry Supply Automation - Keb F5 Drive & Lenze Supplier in the field can provide valuable insights into specific applications and potential solutions.