In short, several questions were asked and in the end it was determined that it was not the motors fault nor was it the fan manufacturer’s fault. Motor winding failure can and will occur if certain steps are not followed when installing VFD’s.

First and foremost, the electrical engineer should verify the distance between the VFD and the motor it is controlling. Voltage spikes caused by excessive distance can kill a motor and it can happen in a short period of time. To prevent premature winding failure, review the VFD manufacturer’s recommendations for proper distances. A rule of thumb is less than 150 feet. The shorter the distance the better chance there will be less voltage spiking during operation. The longer the distance, the greater the voltage spikes from the VFD.

Second, and just as important, make sure the motor that is selected for the fan is inverter duty rated and has the correct insulation class rating for the windings. There are three common insulation classes that most manufacturers provide. Class B would be the lowest insulation factor and is often recommended for non-inverter duty applications. The insulation on the windings is not capable of handling voltage spikes from a VFD control. Class F would be the second highest insulation rating and is capable of handling voltage spikes. Class H would be the highest rating and is recommended for severe high heat conditions and in applications where the VFD control will be adjusting speeds on a continual basis during operation.

Lastly, if the motor speed will be adjusted continuously by the VFD, such as with variable air volume systems, it is recommended to use a motor shaft grounding device. Shaft grounding will eliminate induced motor shaft currents which discharge through the bearings. Motor shaft currents cause pitting, fluting, and catastrophic motor failure. Providing motors with shaft grounding rings will prevent these harmful currents from destroying the motor bearings and extend the life of the motor.

For more information on VFD motor failure and shaft grounding rings please clink on the links below.

VFD and Motor Failure – http://www.yaskawa.com/site/dmdrive.nsf/link2/MNEN-5JFQPL/$file/AR.AFD.05.pdf

Shaft Grounding – http://www.est-aegis.com/markets/hvac.htm

- By Jeff Dubecky

Building on our 35-years of expertise and outstanding staff tenure, we bring leadership and detailed services to our valued clients and manufacturing partnerships.  We service three metropolitan areas, Cleveland, Columbus and Toledo, with superior air control and movement needs.

Working with our customers to match the proper product with the proper application, Air Control Products has gained a reputation for original approaches to motion design technology.  Engineers rely on us to solve their air movement requirements. All the products we represent are extremely durable, rugged, and designed to last.

Our new website, launching later this month, will give you an overview of our business and what products we have to offer. I invite you to visit it and let us know if there are any air movement needs we can help you with! Please visit our website at www.aircontrolproducts.com for more information. When our new website launches you will have the opportunity to learn more about our open house on October 5 & 6, as well as how to qualify for some great prizes!

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