April 9, 2012

Causes of Fault in Power System Components


OVERHEAD LINE FAULTS 
  1. Lightning surge overvoltage cause by shielding failures or black flashover events which are transient in nature, being 80-90% of overhead line faults. 
  2. Overloading beyond thermal limits.
  3. Conductor mechanical failures resulting from creeps, vibrations, joint and fitting fatigue.
  4. Pollution of insulators by salt, conductive dust, cement dust and other chemicals.
  5. Projectiles and bush fires etc.
  6. Support structure failures caused by storms etc.
  7. Faults caused by animals.
 
CABLE FAULTS
  1. Accidental contact which refers to damage caused by excavation operations either resulting in immediate failure or minor damages such that some considerable time may elapse before insulation fails. 
  2. Ageing and wear.
  3. Faulty insulation.
  4. Lightning surge overvoltage.
  5. Insulation failure due to ingress of moisture, loss of dielectric impregnant and internal ionization (partial discharge).
  6. Faults in joints and terminations.
  7. Overloading resulting in overheating and thermal run-way.
  8. Thermomechanical movements and subsidence.
  9. Corrosion, vibrations etc.
 
TRANSFORMER FAULTS
  1. Earth faults in windings. 
  2. Phase to phase faults in windings.
  3. Interturn faults.
  4. Overheating due to overloading or failure of cooling system.
  5. Core faults.
  6. Tap changer faults and mechanism failure.
  7. Low oil.
 
SWITCHGEAR FAULTS
  1.  Leakage of insulant i.e SF6 gas or low oil. 
  2. Salt, conductive dust, cement and other chemical pollutions on outdoor switchgear.
  3. Condensation in indoor switchgear.
  4. Operating mechanism failures.
  5. Contact mechanism failures.
 
BUSBARS FAULTS 
  1. Accidents resulting from human error, phase to earth faults. 
  2. Bridging of air gaps by animal etc, phase to phase faults.
  3. Equipment failure causing busbar faults.
  4. Flashover usually phase to phase faults.
  5. Operational causes.
 
GENERATORS (ALTERNATOR) FAULTS
 
Stators Faults:
  1. Phase to phase faults. 
  2. Phase to earth faults.
  3. Short circuit between turns.
  4. Open circuit in windings.
  5. Overheating.
They can be caused by overvoltage due to transient, lightning and switching surges or sudden loss of load and insulation deterioration.

Rotor Faults:
  1. Winding double earth faults. 
  2. Interturn faults.
 
MOTOR FAULTS
  1. Sustained overloading. 
  2. Single phasing i.e. operation of motor with only two effective phases connected due to a blown fuse or open circuit winding.
  3. Phase to earth faults on windings and connections.
  4. Phase to phase faults on windings and connections.
 
Apart from these, faults can be caused by the propagation of system overvoltage resulting from:
  • Phase to phase and phase to ground faults. 
  • Overspeeding of generators due to load rejection.
  • Switching surges.



fault current, causes of fault, causes of fault current, overhead line fault, cable fault, transformer fault, busbar fault, switchgear fault, generator fault, motor fault
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