Electrical motors are essential components in many industrial & commercial applications, & like any machinery, they can develop problems with time.
Efficient motor troubleshooting necessitates a methodical approach to identifying fundamental issues and developing corrective measures.
What is the most common cause of Motor Failure?
Low resistance as a result of insulation breakdown is the primary cause for motor failure. Insulation breakdown in motors is typically brought on by overheating, corrosion (or) physical damage.
The windings of the motor will experience leaks and short circuits as a result of this occurrence.
Electrical Motor Troubleshooting
An Electrical Motor Troubleshooting Chart is a valuable tool for maintenance personnel and engineers, providing a clear path for diagnosing common motor issues.
This chart describes the signs, possible causes, & recommended correction procedures, which can assist to reduce downtime and maintain the smooth operation of electric motors.
Electrical Motor Troubleshooting Chart
| Failure | Cause | Corrective Measures |
| 1). Failure to start motor | a). There is no voltage supply | Verify the feed connections to the motor and the control system. |
| b). Supply with low voltage | Verify the voltage supply to make sure it stays within 10% of the motor nameplate’s rated voltage. | |
| c). Incorrect control connections | Verify connections against the motor nameplate’s wiring diagram. | |
| d). Loose connection at a terminal lug | Tighten every connection. | |
e). Over-load | Try starting the motor without any load. If it starts, its starting mechanism might be blocked or there might be an overload problem. Increase torque while lowering the load to the rated load level. | |
| f). Brushes | Brushes could be unclean, worn out, or not fitting properly. | |
| 2). High Level of Noise | a). Imbalance | Balance the rotor to eliminate vibrations. If the load is directly linked to the motor shaft, it may be imbalanced. |
| b). Shaft that has been distorted | The shaft can be bent; check the rotor balance & eccentricity. | |
| c). Inaccurate alignment | Check the motor alignment while the machine is running. | |
| d). Inconsistent air difference (air gap) | Check the shaft for warping (or) bearing wear. | |
| e). Dirt in the air space (air gap) | Disassemble the motor and clean any debris or dust with a spray of dry air. | |
| f). Extraneous matter is lodged between the motor casing and the fan. | Dismantle and clean the motor. Remove any garbage or debris from around the motor. | |
| g). Motor foundation that is loose | Tighten the foundation studs. If necessary, readjust the motor. | |
| h). Bearings that have been worn out | Check the lubricant. Replace the bearing if the noise is strong and continuous. | |
| 3). Bearing Overheat | a). Excess grease | Remove the grease bleeder plug & run the motor until the excess grease is discharged. |
| b). High axial (or) radial strain on the belt | Reduce the belt tension. | |
| c). A deformed shaft | Have the shaft straightened and verify the rotor balance. | |
| d). Rough bearing surface | Replace the bearings before they degrade the shaft. | |
| e). Loose (or) improperly installed motor end shields | Check end shields for a close fit around the circle and tightness. | |
| f). Lack of grease | Add grease to the bearing. | |
| g). Balls freeze up due to hardened grease | Replace the bearings. | |
| h). Foreign substance in grease | Flush the housings & re-lubricate. | |
| 4).Intense Bearing Vibration | a). Unbalanced Rotor | Balance the rotor statically & dynamically. |
| b). Dirty (or) worn bearings | If the bearing rings are in fine condition, clean and re-lubricate it; otherwise, replace the bearing. | |
| c). Bearing rings are overly tight on the shaft and/or bearing housing. | Before adjusting shaft (or) housing dimensions, ensure that the bearing dimensions match the manufacturer’s specifications. | |
| d). Extra solid particles in bearings. | Take apart and clean the bearing. Reassemble only if the spinning & support surfaces are undamaged. | |
| 5). Motor Overheating | a). A cooling system that is obstructed. | Regularly clean and dry the motor, and inspect the air vents and windings. |
| b). Overload | Check the application by measuring voltage & current under normal operating conditions. | |
| c). Inaccurate frequencies & voltages | Compare the values on the motor nameplate to those of the mains supply. The motor terminal voltage should also be checked while the motor is operating at its maximum load (full load). | |
| d). Periodic inversions | Replace the motor with another that matches your demands. | |
| e). Rotor dragging on a stator | Inspect bearing wear & shaft curvature. | |
| f). Electrical load imbalance (incorrect control, burned fuse) | Check for imbalanced voltages (or) operation in single-phase mode. | |
| 6). Slip Ring Motor with Disconnected External Resistance Running at Low Speed | a). Control circuit (CC) conductors are too light. | Use heavier conductors on the control circuit. |
| b). Control is too far from the motor. | Move control closer to the motor. | |
| c). Open circuit on the rotor circuits (which includes connections to control equipment). | Test the circuit using a magneto (or) other means & make any necessary repairs. | |
| d). Dirt between the brush and slip ring. | Clean the slip rings and insulating assembly. | |
| e). Brushes grab the brush holds. | Choose brushes of the appropriate size. | |
| f). Incorrect pressure on brushes. | Check the pressure on each brush & adjust accordingly. | |
| g). Roughness on slip rings. | File, sand, & polish. | |
| h). Eccentric rings. | Turn on a lathe (or) use a portable tool without departing from the machine. | |
| i). Excessive current density on brushes. | Reduce the load (or) change brushes. | |
| j). Brushes are not properly configured. | Reset the brushes correctly. | |
| 7). Sparking Brushes | a). Inadequately pressured brushes that are poorly set | Check the brush setting and make the necessary pressure adjustments. |
| b). Overload | Install a motor with a high capacity (or) reduce the load. | |
| c). Poorly maintained slip rings. | Reset brushes and clean rings. | |
| d). Oval slip rings. Scored rings & rough surfaces. | Use an emery to polish the slip rings, then machine them on a lathe. | |
| e). Too Much Vibration | Check for free movement of the brushes within the holders and balance the rotor. |
How to megger a 3 Phase Motor?
- Ensure that the motor is disconnected from the power supply.
- The instrument used to measure insulating resistance is called a megger measure.
- Connect the positive lead of the megger to the winding of the motor and connect the negative lead of the megger to the frame of the motor.
- The voltage of the megger should be applied, and the insulation resistance reading should be recorded.