Examples of common electric motor failures and how to fix them

All electric motors have a predetermined service life, which generally varies from 30,000 to 40,000 hours. However, this depends on proper maintenance, without which they are likely to break down much faster. Understanding common electric motor failures and their root causes, as well as the steps that can be taken to reduce the risk of these failures occurring, will give your motor the best chance of achieving the maximum possible life and performance.

Common failures in electric motors

The most frequent faults in electric motors that can occur in both three-phase and single-phase induction equipment are as follows:

• Blown fuses.
• Worn bearings or cushions.
• Interruption of some phases.   
• Overloads.
• Inverted phases.
• Short circuit.
• Wrong internal connections.
• Winding earthing contacts.
• Excessively tight cushions.
• Poorly fitted covers.
• Bent axle.
• Rotor bars loose.
• Defective capacitor (on single-phase motors with capacitor).
• Interruption in the starting winding (in single-phase motors).
• Interruption in the working winding (in single-phase motors).

Electrical overload

Electrical overload is caused by excessive current flow within the motor windings, which exceeds the design current that the motor can carry efficiently and safely. This can be caused by low supply voltage, resulting in the motor drawing more current in an attempt to maintain its torque. It can also be the result of shorted conductors or excessive supply voltage.

Low resistance

The most common cause of electric motor failure, and possibly the most difficult to overcome, is low resistance. Low resistance is caused by degradation of the winding insulation due to conditions such as overheating, corrosion or physical damage. This leads to insufficient insulation between the conductors or windings of the motor, which can cause leakage and short circuits, and eventually motor failure.

To avoid such failures in electric motors we recommend that the insulation should be periodically inspected for signs of wear and replaced before low resistance can cause failure.

Overheating

About 55% of insulation failures in electric motors occur due to overheating. Overheating can be caused by poor power quality or a high temperature operating environment. For every 10°C increase in the temperature of a motor, the lifetime of the insulation is reduced by 50%.

Pollution

Dust, dirt and chemical contamination is one of the main causes of main causes of electric motor failure. Foreign bodies that find their way into the engine and can affect the raceways and bearing balls, leading to high levels of vibration and wear. It can also block the cooling fan, which limits the engine's ability to regulate its temperature and increases the likelihood of overheating.

Vibrations in electric motors

Vibration can lead to many problems with the engine, and can eventually cause the engine to fail prematurely. Vibration is often caused by the position of the engine on an uneven or unstable surface. However, vibration can also be the result of an underlying problem with the engine, such as loose bearings, misalignment or corrosion.

Engines should be regularly checked for vibration, using a engine vibration analysis tool. To reduce vibration, make sure the engine is placed on a flat, stable surface. If vibration still occurs, check for signs of wear, such as loose bearings or misalignment. Consider contacting a specialist if the source of vibration cannot be identified.

A basic principle for the detection of faults in electric motors is the observation of the daily operation of the motors and, in addition, the drawing up of an inspection programme for the motors based on their service conditions. Eventually, the frequency of inspection can be based on the experience of the out-of-service times of the motors. Periodically, the following should be checked.

9 points to check to avoid electric motor failures

• General cleanliness.
• Electrical conditions.
• High ambient temperatures and proper ventilation.
• Alignment with the load.
• Proper lubrication and wear of engine bearings and load.
• Deterioration of winding insulation.
• The condition of the rotor.
• Wear and tear on switches.
• Deterioration of capacitors (if any).

For more information and solutions to detect and prevent electric motor failures, subscribe to the Technology for Industry newsletteror seek expert advice on the design of electric motor applications.