Written by Justien Kint, maintenance and engineering expert
Electric motors are used in industry around the world to drive fans, pumps, compressors and more.
To help plants and factories get the most out of the motors they have, I’ve collected a handful of tips in this post (primarily focused on IEC low-voltage motors). By carefully applying these tips in practice, you’ll significantly improve the reliability and lifespan of your electric motors, and also lower your energy costs—of that I’m convinced.
Every electric motor is equipped with two bearings: one on the non-drive end (NDE) and one on the drive end (DE). Depending on the type of bearing, it will need periodic relubrication. Keep in mind that the NDE bearing often needs a different amount of grease than the DE bearing (this tends to be forgotten). How often you need to relubricate depends on a number of factors, including whether the motor is vertical or horizontal, the temperature of the surrounding environment, the motor’s speed, how often the motor runs, the number of starts and stops, and so on.
Tip: the manufacturer often attaches a nameplate to the motor that will tell you which bearings are used, the recommended lubricant and roughly how often to regrease. See the photo below. Respecting the manufacturer’s recommendations and following them as closely as you can is already a very good step toward extending the motor’s reliability and lifespan, but for critical motors I’d recommend ultrasound assisted lubrication, if you want to achieve world-class maintenance (WCM; more on that here.) These days there are also specialized machine learning solutions you can buy, which among other things can remotely alert you when your motor is in need of regreasing.
The cooling ribs and fan serve an important role: removing the heat generated by the motor. If the motor can’t get rid of its heat, its life expectancy will plummet, and sooner or later the heat will cause the motor to malfunction. Its energy consumption will also rise unnecessarily. Depending on the operating context (a term from reliability centered maintenance, or RCM), dust buildup is a failure mode you must take very seriously and one where regular maintenance is well worth the effort. If dust is allowed to clump on the cooling fan, for example, it will throw the motor out of balance; the resulting vibrations will disturb the electrical connections, which may cause them to break or come loose. If dust is allowed to completely cover the cooling ribs, the motor will rapidly heat up, which can lead to an HH temperature trip and premature failure due to overheating components in the motor.
The video below contains an example of extreme dust buildup in the cement industry. If you truly want to improve reliability, this is a completely unacceptable situation. Companies that take reliability seriously will take real steps to prevent dust buildup as much as possible or to regularly remove it. Those who don’t will pay the piper later. (Reliability is, more than anything, a question of culture; it requires a specific kind of company mindset.)
Depending on the application, motors controlled by a variable frequency drive can experience stray current running through the bearings. Bearing current can be a serious problem. I’ve seen it many times in the field, even in motors using an insulated bearing. (Manufacturers often use an insulated bearing on the NDE: the cage is coated with a layer of insulating material.)
Stray current is truly deadly to bearings. They will fail prematurely and the current that killed them is betrayed by the washboard pattern seen inside the rings of the disassembled bearing, often combined with the smell of burnt grease.
To prevent this, the first step is to determine for each motor whether stray current is flowing through the bearings. Specialized companies can diagnose this for you, or you can eventually figure it out yourself if the bearing repeatedly gives up the ghost. (Tip: be sure to perform a thorough post-mortem on the bearing.) If you determine that current is running through the bearing, you’ll need to take measures to stop it. The company that diagnosed the problem can assist; there are also helpful resources on the web if you plan to solve the problem yourself.
Electric motors are often coupled to a pump, fan, compressor or other piece of equipment. Proper alignment is essential for high reliability and a long life. But there’s a caveat: good alignment can only happen if the foundation is up to snuff; otherwise aligning the system will be a study in frustration. For that reason, make sure the foundation is smooth, level and vibration-free. And always take the time to align equipment properly and precisely using laser alignment, or you’ll have to pay the piper again later in the form of premature failure.
Sadly, electric motors are often improperly dimensioned. Underdimensioned motors are prone to overheating, and the motor may not be able to meet the demands of the application; overdimensioned motors are unnecessarily expensive to buy. Nor do overdimensioned motors provide a good return on investment. Paying appropriate attention to motor size in the design phase can make an enormous difference in both the cost to purchase the motor and its energy consumption during use.
I hope this post has given you some good ideas, and that you’ll put them into practice! Have any tips of your own to share? I’d love to hear them at email@example.com.
Justien Kint has over a decade of experience in maintenance engineering and industrial asset management. As an expert consultant, he helps companies plan and implement maintenance strategies tailored to their critical assets. His clients span a wide range of industries including food and chemical processing, steel manufacturing, infrastructure, offshore and public transport. Read more at www.iammaintenance.nl.