Motor Life Expectancy

What can you reasonably expect and how do you optimize it?

Part 1 of a 3 part series on motor life expectancy 

As you would expect motor life expectancy is highly variable and dependent on numerous factors. Many motors fail prematurely due to misapplication and this series will discuss ways to avoid these and optimize motor life. This avoids costly downtime and the expense of repair or replacement.

As you can see from the above chart, the most common cause of failure in AC induction motors are related to windings and bearings. We will first focus on failures related to motor windings.

Motor insulation temperature rise ratings vary as illustrated below for Class B and Class F insulation.

Note: Class H insulation has an even higher temperature rating than Class F (190 Degree C vs 155 Degrees C). Insulation life is reduced dramatically when temperature ratings of the Insulation are exceeded!

Common causes of Motor Winding Failures and their Solutions

Motor overloading is caused by torque loads exceeding the nameplate rating. This results in excessive current draw which rapidly overheat the motor winding.

There are a number of ways to solve this issue which include sizing the motor properly to the connected load; extending the acceleration time when the motor is operated on a VFD; using a higher gear ration, where feasible, when load is driven by a gear or belt drive.

Other methods of mitigation the overheating of motor windings include using a properly sized motor starter or, when operating the motor on a soft start or VFD, making use of the built in current sensing protective features; utilizing winding temperature sensing devices, such as PT100 RTDs or thermistors to protect the winding from overheating. The final option is to rewind the motor using a higher class of insulation.

Shorted motor windings can occur phase to phase, turn to turn or winding to stator. A short can be caused by contamination from the environment which may call for a tighter motor enclosure type.

A shorted winding could also be caused by abrasion which may be due to high vibration present in the application. This issue may require special motor construction.

The in-house technical specialist at Flolo have extensive knowledge of motor failures common across a broad range of industries and solutions that will maximize life expectancy in these demanding applications. Additional information on how to best optimize motor life are covered in extensive detail in classes available thru Flolo Tech. Please contact your Sales Representative for additional details.