Factors affecting breakdown Strength of dielectric material : 



A) Solid dielectric material:
1) Thickness of Specimen.
2) Area and volume of solid dielectric.
3) Defect and non-homogenetly of material.
4) Shape of electrode.
5) Time of application of voltage.
6) Time (duration) of test voltage.
7) Electrode surface condition.
8) Method of placing the electrode.
9) Moisture and other contamination.

B) Liquid dielectric Material :
1) Dissolved gas increase breakdown Voltage decrease.
2) Distance between electrode increase breakdown .
3) Dust and dirt increase breakdown Voltage decrease.
4) Moisture or water particles decrease breakdown Voltage.
5) Impurities increase breakdown Voltage decrease.
6) Temperature affect .
7) Shape of electrode.
8) Viscosity of liquid.
9) Electrode materials.

C) Gaseous dielectric Material : 
1) Electrode configuration.
2) Gap spacing is increase breakdown Voltage is increase.
3) Pressure:- According to Paschen's law increase or decrease in pressure leads to increase breakdown Voltage.
4) Moisture and humidity is inversely proportional to breakdown Voltage.
5) Effects of atmospheric condition.