Question

Explain the reasons for failure of gaseous and solid dielectric materials used in electrical engineering application. 

Answer 1

Reasons for failure of gaseous and solid dielectric materials used in electrical engineering application.

1. If the system voltage increases more than breakdown voltage for some interval then there are chances of dielectric failure 

2. Long time partial discharge in solid insulator will create dielectric failure. 

3. Due to super heating of dielectric material i.e. due to heavy load or over load temperature increases and dielectric failure occurs. 

4. Due to lighting surge there may be possibility of dielectric failure. 

5. Due to short circuit or ground fault there may be possibility of dielectric failure. 

6. Due to poor maintenance of insulating material there may be possibility dielectric failure

OR

Failure of gaseous dielectric or Breakdown of gaseous dielectric depends on following factors: 

1. Breakdown voltage depends on the frequency of the applied voltage.

 When frequency is increased breakdown voltage decreases.

2. It depends on distance between the electrodes & the chemical composition of the gas.

3. It also depends on shape & size of electrodes.

4. It also depends on uniformity of the applied electric field.

5. It also depends on pressure. 

Failure in solid dielectric or Breakdown in solid dielectric depends on : 

Three types breakdown. 

i)Electro-thermal ii) purely Electrical iii) Electro – chemical 

1. Electro-thermal breakdown is due to the heat produced by the dielectric loss which is due to the heat produced by the dielectric loss which is proportional to the intensity of the electrostatic field &frequency. 

2. Purely electrical breakdown is due to collision ionization by electrons. When the free electrons in the crystals are accelerated by the strong electric field K.E. increases and collision occurs. 

3. Electro chemical breakdown usually occurs at very high temperature and high humidity of the surrounding air