Dielectric Breakdown – Definition and Types

Types of dielectric breakdown,

1. Intrinsic breakdown
2. Thermal breakdown
3. Electrochemical breakdown
4. Defect breakdown
5. Discharge breakdown

Intrinsic Breakdown

When a dielectric material is subjected to large electric field, a large number of electrons are transferred from the valence band to the conduction band and becomes conducting material. Thus the dielectric material loses its insulating property. This is known as intrinsic breakdown.

Further the conducting electrons may collide with the atoms and release some of the valence electrons. These electrons may collide with some more atoms and may release more electrons. This becomes a chain process resulting in a large current. It is known as avalanche breakdown.

Characteristics

• Occurs at room temperature and low temperature.
• Occurs at high electric field in few milli seconds.

Thermal Breakdown

When a voltage is applied to the dielectric material, heat is produced. If this heat is not dissipated away, then this dielectric breakdown occurs.

Characteristics

• Occurs only at high temperature.
• Occurs at moderate electric field in few milli seconds.

Electrochemical Breakdown

When temperature increases, mobility of ions increases and hence leakage current also increases. This decreases the insulation resistance and finally creates a dielectric breakdown.

Characteristics

• Occurs in pure dielectric materials.
• It should not operated at high temperatures.

Discharge Breakdown

When dielectric materials have occluded gas bubbles and when they applied to high voltages, electrical discharge takes place. It produces a large ionization current. This is called discharge breakdown.

Characteristics

• Occurs at low voltages with more number of gas bubbles .
• It depends on the frequency of applied voltage.

Defect Breakdown

Some dielectric material may have surface defects like cracks, pores, etc. Moisture and other impurities can fill at these places leading to breakdown. This is called defect breakdown.

Remiedies to avoid dieletric break down

In order to avoid while choosing the dielectric materials.

1. It must have low dielectric loss and low density.
2. It should be fire proof and resistive to oils, liquids and gases.
3. It must have high resistivity to reduce leakage current.
4. It should be in pure form without any defects.
5. It must have small thermal expansion and enough mechanical strength
6. It should have high dielectric strength