Causes and Effects of Faults & Faults in a System In a Year

Table:- 01 Causes and effects of faults

Sr. No.

Causes of Faults



Insulation or conducting path failure

Short circuit

  1. Damage the equipment or element due to overheating & high mechanical forces

  2. Arc formation cause a fire 

  3. Reduction or unbalancing in supply voltage

  4. Loss of system stability

  5. Interruption of supply to consumers.


Tree branches or other conducting objects falls on overhead lines or if conductors are broken and if it falls on the ground or joint failures or Birds if touches in between two live wires or one live wire and earth etc


Other causes as on overhead lines: direct lightning strokes, aircraft, snakes, ice and snow loading, abnormal loading, storms, earthquakes, creepers etc


In the cases of cables, transformers, generators and other equipments: failure of solid insulation due to aging, heat, moisture or overvoltage, mechanical damage, accidental contact with earth or earthed screens, flashover due to overvoltages etc


Over-voltage on transmission and distribution lines due to lightning or switching surges or by external conducting objects falling on overhead lines

Flashover on the surface of insulators resulting in short circuit or punctured or breakdown.


Certain foreign particles such as dust or cement in industrial areas or salt in coastal areas or any dirt accumulates on the surface of insulators

Reduces insulation strength and causes flashovers


Opening of one or two of the three phases

System unbalanced form a unbalanced current which set up harmonics, thereby heating the machine

Table:- 02 Faults in a system in a year

Sr. No.


Causes of Faults

% of Total faults


Overhead Lines

  1. Lightning strokes

  2. Storms, earthquakes, icing

  3. Birds, trees, kites, aeroplanes, snakes etc.

  4. Internal overvoltages

30 – 40


Underground Cables

  1. Damage during digging

  2. Insulation failure due to temperature rise

  3. Failure of joints

8 – 10


Alternator (Generator)

  1. Stator and rotor faults

  2. Abnormal conditions

  3. Faults in associated equipment

  4. Faults in protective system

6 – 8



  1. Insulation failure

  2. Faults in tap-changer, bushing, protective circuit

  3. Inadequate protection

  4. Overloading, Over-voltage

10 – 12



  1. Over-voltages

  2. Insulation failure

  3. Breaking of conductors

  4. Wrong connections

15 – 20



  1. Insulation failure

  2. Mechanical defect

  3. Leakage of air / oil / gas

  4. Inadequate rating

  5. Lack of maintenance

15 – 20