By Kevin Bachhofer & Mike Switzer, Operations Manager & Product Line Manager
The following article was previously published by Utilities Tech Outlook. Read the original article here.
Electric motor owners often ask how long their motors will last under current conditions. An exact timeline cannot be determined, but by identifying the most common, avoidable electric motor issues, we can prevent premature failures. Adhering to proper maintenance practices can extend run life and help prevent unwanted failures, be it electrical or mechanical. Let’s review these common issues and discuss how to prevent them from becoming a problem for your business.
Electrical Motor Issues
Common electrical issues in motors often involve multiple factors like poor connections, overload conditions, phase imbalance, and incorrect voltages. Ensuring that the motor is properly connected electrically by torquing lead connections to the proper specification is extremely important. This prevents the creation of a high resistance connection, which is a hazard. HRCs can cause enough heat to start a fire that could damage more than your motor.
Other electric motor issues, such as an overload condition and heating, can be prevented by applying the correct horsepower and torque requirements to the motor based on the nameplate ratings. Limit how often the motor is started before the recommended cooldown time to prevent damage. Excessive or frequent starts will create heating in the stator iron core, which will lessen the insulation life of the motor’s coils. This issue often arises on motors powered in what is commonly referred to as “across the line” starting condition where full voltage is applied to the motor at the instance of startup. A soft start or a VFD would eliminate the potential damage caused by the initial surge for across the line starts.
Phase imbalance (under voltage or over voltage) on the phases is also a detrimental electric motor issue, causing higher than normal current in the motor. Motor circuits equipped with VFDs can be programmed to watch for and shut down in the event fluctuations or imbalances are detected. In reference to a VFD application, it should be noted that the VFD should have some type of induction absorption or output filter between the component to the motor. A VFD without filtering can produce circulating currents from bearing to motor shaft, which will shorten the life of the bearing. Several motor manufacturers add grounding rings to their motors along with insulated bearings to stop the circulating currents that unfiltered VFDs may cause, which could lead to a motor failure.
Mechanical Motor Issues
Mechanical failures are all too common with anything that has physical movement. Avoiding premature failure can give a motor a long life. Lubrication is one of the most important procedures that should be considered. Ball bearings are lubricated from the manufacturer’s factory, but this does not mean that they are lubricated for the life of the motor. It is vital to maintain recommended lubrication to avoid bearing failures. The same reasoning applies to sleeve style bearings and rolling style bearings that are lubricated with oil. Periodic oil changes for a sleeve/rolling element bearing can increase the life of the bearings.
Keeping the motor aligned can also have a profound effect on how long the bearings last. Proper alignment varies widely between installations as the motor must be set to grow to a thermal position at which time the desired alignment is achieved. A good alignment is necessary for a motor to successfully operate up to and beyond its intended life cycle. During your annual checks, confirm the motor’s alignment and test vibration.
Vibration can be detrimental to bearings and create bearing fatigue. Sometimes, this can be the first indication that something is wrong internally. Within the motor itself, make sure the bearing fit tolerances and all seal areas are correct. Excessively loose bearing fits can cause vibration in the motor and begin to wear other tolerances on the motor, such as seal clearances causing leaks, premature failure, and costly repairs. Conversely, tight bearing fits can reduce oil clearances, increase heating, wipe out bearings, and even result in shaft damage. Annual bearing inspections can detect changes and signs of wear that may go unnoticed until it is too late.
Heating and Cooling Motor Issues
A totally enclosed fan-cooled (TEFC) motor is dependent on the airflow of an external fan to cool the outside frame of the motor, thus cooling the inside air through heat transfer. Keeping the vents clear of dirt and debris will allow the motor to cool as intended. Routine inspection of fan blades will ensure the motor air flow remains at or near factory recommendations.
Larger motors have top hats or hoods. These hoods typically have provisions for some type of air filtration. Varying sizes of filters are used in these kinds of applications and are typically made of aluminum or stainless-steel material for the filtered mesh. Either type can be extracted, cleaned, and re-installed to help the motor breathe and keep cool. If a motor does not have filters, it can draw in the surrounding dust and debris. This will accumulate inside the motor and create heat within the motor by encapsulating the windings and plugging stator vents. The heat in the stator will become trapped with no way to dissipate. This can also lead to dirt buildup inside the rotor, creating a vibration issue as well. Simple, routine maintenance and cleaning of the filters avoids nearly all these potential electric motor issues.
The last common avoidable electric motor issue involves allowing motors to be placed too close together in their respective applications or installed in an enclosed, hot environment. These motors can pull in hot air versus cooler, ambient air if placed in a configuration that allows a motor to intake the exhaust of a motor in proximity. This may also alarm or trip the monitor device being utilized, causing unwanted shutdowns and unnecessary restarts on equipment. Site planning and additional ventilation for nearby motors can prevent this issue from happening.
In summary, keeping your motors running as efficiently as possible will allow your business to focus on areas that may have been neglected in the past. At Southwest Electric Co, our in-house repairs will get you started in the right direction. We also offer turnkey installation services and maintenance plans to help your assets run longer and more efficiently. Give us a call to discuss your facility and electric motor issues, and we will customize a plan that will improve the lifespan of your equipment.
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