Breakdown in Solids

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Breakdown in Solids

  • The mechanism of breakdown in solids is less understood because of it complexity.
  • When breakdown occurs gases regain their dielectric strength fully, liquid partially and solid lose their dielectric strength completely. It is permanent breakdown.

Breakdown depends upon :

  1. Magnitude, time of voltage applied, A.C, D.C, or impulse voltage applied.
  2. Ambient temperature, humidity.
  3. Impurities or structural defect, pressure applied to electrode.

Time of application plays aim important role in breakdown. According to time of application different breakdown mechanisms occur.

  1. Intrinsic breakdown
  2. Electromechanical breakdown
  3. Breakdown due to treeing and tracking
  4. Thermal breakdown
  5. Electrochemical breakdown
Breakdown in Solids

Properties

  1. Good dielectric should have low dielectric loss.
  2. High mechanical strength.
  3. Should be free from gaseous inclusions and moisture.
  4. Resistance to thermal and chemical deteriotion
  5. Low permittivity to keep the corrosion between conductor loss.
  6. A low P. F. to reduce treeing effect.
  7. High insulation resistance.
Applications
  1. Used in almost all electric equipments such as heater, generators, circuit breakers.
  2. Also provides mechanical support to the equipment.

Intrinsic breakdown

  1. When solids are tested for breakdown under carefully controlled laboratory conditions, extremely high strengths in the range of 1 MV/cm to 15 MV/cm can be obtained.
  2. If the strength is solely dependent on the chemical. Corrosion and dielectric properties of the material, than it is known as its intrinsic electric strength.
  3. The mechanism of intrinsic breakdown of solid is an electronic phenomenon and is completed in a very short time of the order of 10 second.
  4. Two types of intrinsic breakdown are been proposed by Frochlich’s theory.

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