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The phenomenon of intermittent arc taking place in line to ground fault of a 3-phase system with consequent production of transients is known as:
1. resonance
2. insulation failure
3. arcing ground
4. current chopping

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Correct Answer - Option 3 : arcing ground

Causes of overvoltage:

The abnormal overvoltages may be caused due to various reasons such as sudden interruption of heavy load, lightning impulses, switching impulses, etc.

The overvoltage of a power system may be broadly divided into two main categories viz.

Internal Causes:

Switching Surges: The overvoltages produced on the power system due to switching operations are known as switching surges.

Insulation Failure: The most common cause of insulation failure in a power system is the grounding of the conductor (i.e. insulation failure between line and earth) which may cause overvoltages in the system.

Arcing Ground:

  • The phenomenon of intermittent arc taking place in the line-to-ground fault of a 3phase system with consequent production of transients is known as arc ground.
  • This happens when there is the presence of a sporadic arc in line-to-ground fault belonging to a three-phase system.
  • Here, short-lived oscillations are produced in the system due to some changes in the voltage and the current load.
  • This phenomenon may lead to serious problems like the breakdown of the insulation and may harm equipment connected to the power system.


Resonance: This one occurs when the value of the inductive resistance in the power system becomes equal with the value of capacitive resistance.

External Causes:

This type of overvoltages originates from atmospheric disturbances, mainly due to lightning. This takes the form of a surge and has no direct relationship with the operating voltage of the line. It may be due to any of the following causes:

  • Direct lightning stroke.
  • Electromagnetically induced overvoltages due to lightning discharge taking place near the line, called 'side stroke'.
  • Voltages induced due to atmospheric changes along the length of the line.
  • Electrostatically induced voltages due to the presence of charged clouds nearby.
  • Electrostatically induced overvoltages due to the frictional effects of small particles like dust or dry snow in the atmosphere or due to change in the altitude of the line.

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