The 12 most common industrial electric motor faults and how to identify them

When industrial electric motor failures occur, production work often comes to a halt until they are up and running again, and the reasons for the failure of an electric motor can vary from the common to the bizarre.

While the list of possible causes can go on forever, we will look at some of the most common ones here:

1. High temperatures and heat. Exposure to high temperatures is the main culprit in all types of electric motor failure and ranks as the number one reason for motor malfunction and deterioration. Optimum operating temperatures extend the life of the motor and should be the first priority of every maintenance technician.

In fact, most of the other possible reasons for electric motor malfunction also lead to additional heat generation. An increase of even a few degrees can cause problems over time, and if the motor windings are exposed to an additional 10 °C the lifetime of the insulation is halved.

2. The engine loses speed. Possible reasons and checks for this type of problem in electric motors are as follows:

• A phase may be open: Check phases to determine if they are open.
• Misapplication: Change of capacity or type.
• Engine overloaded: Reduce the load.
• Low voltage at motor: Check that nameplate voltage is maintained. Check also connections.
• Open circuit: Fuses blown. Check overload relays. Stator and push button station.

3. Exposure to dust and pollutants. Electric motors are often placed in enclosures to protect them from dust and contamination, but tiny particles can still enter them unless the enclosures are protected against ingress to the appropriate standard for the equipment it uses.

Like any other machinery, exposure to dust and contaminants can cause damage to electric motor parts and lead to malfunction. Depending on the type of contaminant involved, damage can range from component wear due to abrasion or corrosion, to current interference due to electrically conductive particles.

4. The engine starts and then stops. Possible power failure, it is recommended to check connections to line, fuses and control.

5. The engine does not come up to speed. Check the following:

• Misapplication: Check phases to determine if they are open.
• Voltage too low at motor terminals, due to voltage drops: Use higher voltage at transformer terminals or reduce load. Check connections and proper sizing of feeder conductors and/or branch circuit.
• Start-up load too high: Check the load the engine is supposed to be able to handle.
• Broken rotor bars or loss of rotor: Check for fractures near the rings.
• Opening in primary circuit: Locate fault with test devices and repair.
  In general, when an engine has problems, the service technician must decide whether it is worth rebuilding the engine or buying a new engine. The use of a decision flow chart can help guide this decision.

6. The engine takes too long to start. Possible reasons and checks for this type of problem in electric motors are as follows:

•  Excess load: Reduce the load.
• Poor circuit: Check for high resistance value.
• Squirrel cage rotor defects: Replace with a new rotor.
• Voltage applied too low: Check that the supplying company of the appropriate value.

7. Incorrect direction of rotation. If the phase sequence is incorrect: Change the connections on the motor or on the board.

8. The engine overheats while under load. It may be due to:

• Overload: Reduce the load.
• The housing or ventilation slots may be clogged with debris or dust: clean and check for air circulation.
• The motor may have an open phase: Check that all conductors are connected correctly.
• Earth coil: Locate and repair.
• Unbalanced terminal voltage: Check for faulty conductors, connections and transformers.

9. Engine vibrates after correction has been made. It may be:

• Misaligned engine: Realign.
• Weak support: Strengthen the base.
• Out-of-balance coupling: Balance the coupling.
• Unbalance in the driven equipment: Rebalance the above-mentioned equipment.
• Bearing and bearing failures: Replace bearings.
• Bearings not aligned: Align bearings.
• Single-phase motor operating on one phase: Check for open circuits.
  

10. Unbalanced line currents in polyphonic motors during normal operation.

• Different terminal voltages: Check conductors and connections.
• Single-phase operation: Check open contacts.
  

11. Junk Noise

• Loose fan: Remove interference
• Faulty fan insulation: Clean the fan

12. Noisy operation

• Non-uniform air gap: Check caps, bearings and bushings
• Rotor unbalance: Balance the motor.

Using the electric motor in the manner suggested by the manufacturer is always the key to preventing failures, especially in terms of correct operating conditions, regular maintenance and timely inspections. Usually, the service technician will encounter more than one when a malfunction occurs, so keep an eye out for any unusual activity!

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