Common Faults and Troubles in DC Machines: Causes and Troubleshooting Tips

Common Faults in Electrical Machines

Electrical machines like motors and generators may face multiple issues during operation. Here are the most common faults along with their causes.

1. Failure to Start

Possible causes:

1. Ground fault
2. Open or short-circuit fault
3. Incorrect wiring or wrong connections
4. Low supply voltage
5. Frozen bearings
6. Excessive mechanical load

2. Sparking at Brushes

Possible causes:

1. Improper brush contact due to low spring tension or incorrect setting
2. Dirt or uneven surface on the commutator
3. Open armature coil under the brush
4. Overloading of the machine

3. Vibrations and Pounding Noises

Possible causes:

1. Worn-out bearings
2. Loose machine parts
3. Contact between rotating and stationary parts
4. Unbalanced armature
5. Misaligned components
6. Loose couplings or mountings

4. Overheating

Possible causes:

1. Continuous overloads
2. Sparking at brushes
3. Short-circuited coils in the armature or field winding
4. Frequent start-stop or reversal operations
5. Poor ventilation or blocked air passages
6. Incorrect voltage supply

Other Minor Fault in DC Machine Operation

5. Abnormal Noise or Humming

Possible causes:

1. Loose core laminations causing magnetic hum
2. Loose mounting or frame bolts
3. High-frequency noise due to VFD systems
4. Phase unbalance in 3-phase supply

6. Low Output or Poor Performance

Possible causes:

1. Partial short in stator or rotor windings
2. Reduced field excitation in generators
3. Broken rotor bars in squirrel cage motors
4. Poor insulation causing leakage current
5. Significant voltage drop due to long feeder lines

7. Excessive Brush Wear

Possible causes:

1. Rough or contaminated commutator surface
2. Incorrect brush grade or material
3. High current density through brushes
4. Incorrect brush spring tension
5. Machine vibration causing irregular contact

8. Frequent Tripping of Protection Devices

Possible causes:

1. Continuous overloading of the motor
2. Ground fault or insulation breakdown
3. Phase unbalance or single phasing
4. Presence of harmonics in supply
5. Incorrect rating or miscoordination of relays and breakers

9. Preventive Maintenance Tips

To avoid most of the common electrical machine faults, follow these preventive measures:

1. Perform regular cleaning of brush and commutator assembly
2. Ensure proper lubrication of bearings
3. Conduct insulation resistance testing periodically
4. Check alignment and balance of rotating parts
5. Avoid frequent start-stop cycles to prevent overheating
6. Ensure proper ventilation and airflow inside the machine casing

Conclusion

Understanding the common faults in electrical machines is essential for ensuring their reliable and efficient operation. Issues like failure to start, sparking at brushes, overheating, vibrations, and poor performance can lead to costly downtime if not identified early. By regularly inspecting components, following preventive maintenance practices, and troubleshooting problems systematically, technicians and engineers can significantly improve the lifespan, safety, and reliability of electric motors and generators.

Whether you're preparing for competitive exams like SSC JE, RRB JE, or GATE, or working in the field of industrial maintenance, a solid understanding of these machine faults will help you both in theory and in practical applications.