The key to minimizing motor problems is scheduled routine inspection and maintenance. The frequency of routine motor maintenance varies widely between applications. Including the motors in the maintenance schedule for the driven machine or general plant equipment is usually sufficient. A motor may require additional or more frequent attention if a breakdown would cause health or safety problems, severe loss of production, damage to expensive equipment or other serious losses.
Written records indicating date, items inspected, service performed and motor condition are important to an effective routine maintenance program. From such records, specific problems in each application can be identified and solved routinely to avoid breakdowns and production losses. The routine inspection and servicing can generally be done without disconnecting or disassembling the motor.
All types of rotating machinery require regular inspections so to maintain their integrity and availability. The maintenance of motor becomes simple and effective with the use of minor and major inspections categorized into levels representing the life of the product, be it running hours or years of installation. For each level, a defined number of inspection points are determined which can be undertaken within a specified time. The aim is not to lengthen the outages but to provide an effective solution that can be accommodated within planned maintenance periods and provide expert support when returning the equipment back on line.
Types of Maintenance
Breakdown maintenance
Breakdown maintenance is basically the “run it till it breaks” type of maintenance mode. No actions or efforts are taken to maintain the equipment till its design life is reached. Advantages are, Low cost, Less staff. Disadvantages are: Increased cost due to unplanned downtime of equipment. Increased labor cost, especially if overtime is needed. Cost involved in repair or replacement of equipment. Possible secondary equipment or process, damage from equipment failure, inefficient use of staff.
Preventive maintenance
It is a daily maintenance procedure (cleaning, inspection, oiling and re-tightening), designed to retain the healthy condition of equipment and prevent failure through the prevention of deterioration, periodic inspection or equipment condition diagnosis by measuring deterioration. Just like human life is extended by preventive medicine, the equipment service life can be prolonged by doing preventive maintenance. It is further divided into Periodic maintenance and Predictive maintenance.
Periodic maintenance ( Time based maintenance – TBM)
Time based maintenance consists of periodically (at pre-determined intervals) inspecting, servicing and cleaning equipment and replacing parts to prevent sudden failure and process problems.
Predictive maintenance
This is a method in which the service life of important part is predicted based on inspection or diagnosis, (for Ex., by testing the condition of the lubricating oil in a vehicle for its actual condition and lubrication properties in a good testing centre instead of changing every 5000kM).
This type of maintenance allows us to use the parts/equipment to the limit of their service life. Compared to periodic maintenance, predictive maintenance is condition based maintenance. Basically, predictive maintenance differs from preventive maintenance by basing maintenance need on the actual condition of the machine rather than on some preset schedule. It is possible to schedule maintenance activities to minimize or delete overtime cost.
Also, inventory and order parts can be minimized as required, well ahead of time to support the downstream maintenance needs. It helps to optimize the operation of the equipment, saving energy cost and increasing plant reliability.
Corrective maintenance
It improves equipment and its components so that preventive maintenance can be carried out reliably. Equipment with design weakness must be redesigned to improve reliability or improving maintainability
Maintenance prevention
It indicates the design of a new equipment. Weakness of current machines are sufficiently studied (on site information leading to failure prevention, easier maintenance and prevents of defects, safety and ease of manufacturing) and are incorporated before commissioning a new equipment.
Preventive maintenance schedule
Preventive maintenance is the maintenance which has to be carried out to the equipment, in a preplanned way before serious breakdown takes place. If a record is maintained for certain measurable parameters like body and bearing temperature, insulation resistance, earth resistance etc., it is possible from the scrutiny of this record to predict the occurrence of future trouble and necessary steps can be taken to prevent the occurrence of serious breakdown.
The interval of doing various maintenance operations, depend upon the type of equipment, ambient condition and other factors. It is difficult to laydown hard and fast rules covering all conditions but for average normal industrial duty under-mentioned time schedule will serve as guide. This can be modified to suit other conditions at site.
Daily maintenance : 1) Examine visually earth connections and motor leads. 2) Check motor windings for overheating. 3) Examine control equipment. 4) Check condition of bearings. 6) Add oil, if necessary, 7) Check end play.
Weekly maintenance : 1) Check belt tension. In the case of sleeve bearing machines the air gap between-rotor and stator should be checked. 2) Blow out dirt from the windings of protected type motors situated in dusty locations. 3) Examine starting equipment for burnt contacts where motor is started and stopped frequently. 4) Examine oil in the case of oil ring lubricated bearings for contamination by dust, grit etc. (this can be roughly judged from the colour of the oil). 5) Check the intensity of vibrations during operation of the motor. 6) Clean filters where provided.
Monthly maintenance : 1) Overhaul controllers. 2) Inspect and clean oil circuit breakers. 3) Renew oil in high speed bearings in damp and dusty locations. 4) Wipe brush holders and check bedding of brushes of slip-ring motors. 5) Check that the connections of temperature detectors and space heaters, where provided, are proper and these are in working order.
Haly-Yearly Maintenance : 1) Clean windings of motors subjected to corrosive or other elements, also bake and varnish them, if necessary. 2) In the case of slip-ring motors, check slip-rings for grooving or unusual wear. 3) Check grease in ball and roller bearings and make it up where necessary taking care to avoid overfilling. 4) Drain all oil bearings, wash with petrol to which a few drops of oil have been added, flush with lubricating oil and refill with clean oil.
Annual Maintenance
Check all high speed bearings and renew, if necessary.
Blow out all motor windings thoroughly with clean dry air. Make sure that the pressure is not so high as to damage the insulation.
Clean and varnish dirty and oily windings.
Overhaul motors which have been subjected to severe operating conditions.
Renew switch and fuse contacts if damaged.
Check oil for its dielectric strength.
Renew oil in starters subjected to damp or corrosive elements.
Check insulation resistance to earth and between phases of motor windings, control gear and wiring.
Check resistance of earth connections, air gaps and condition of all fasteners.
Common Fault in Motor in Industries
What are the most common motor faults in industrial environments?
Overheating, Bearing failure, Electrical imbalances, Rotor or stator faults, Insulation breakdown, Vibration-related damage.
What causes motors to overheat?
Overloading: When a motor runs beyond its rated capacity.
Poor ventilation: Blocked or dirty cooling systems reduce heat dissipation.
Electrical imbalances: Unequal voltage or current in the motor phases.
High ambient temperatures
Frequent starts/stops: These reduce cooling time and increase thermal stress.
What are the signs of bearing failure in motors?
Unusual noises (grinding, humming, or knocking), increased vibration, high operating temperatures, reduced motor speed or efficiency, bearings wear out due to contamination, misalignment, poor lubrication, or excessive loads.
How do electrical faults affect motors?
Reduced efficiency, Motor winding damage, Tripping of protection systems, Shortened motor lifespan
Insulation resistance tests and thermal imaging are effective ways to identify early signs of electrical issues.
What are rotor and stator faults?
Rotor faults involve broken bars, cracked end rings, or misalignment.
Stator faults typically involve insulation failure between windings or coil degradation.
These faults can be caused by mechanical stress, overheating, or poor-quality materials. Motor current signature analysis (MCSA) is commonly used to detect rotor and stator issues.
How important is motor alignment and balance?
Misalignment and imbalance can lead to:
Increased vibration and noise, Accelerated bearing and seal wear, Shaft deflection, Reduced energy efficiency
Precision alignment tools and vibration analysis help ensure correct motor installation and operation.
How can motor faults be diagnosed early?
Vibration analysis, Thermal imaging (infrared), Motor current analysis, Insulation resistance testing, Ultrasonic leak detection
Implementing a predictive maintenance strategy can significantly reduce the risk of catastrophic failures.
What role does vibration play in motor health?
Excessive vibration is both a symptom and a cause of motor faults. It can:
Loosen mechanical components, Accelerate bearing wear, Cause fatigue in motor windings
Using vibration sensors and loggers can help monitor and address these issues early.