The document discusses intrinsic (ionic) breakdown in high voltage engineering, specifically in solid dielectrics under short-duration voltage applications. It explains the phenomenon's dependence on free electrons and details types of breakdown including electronic and avalanche breakdowns. The maximum electrical strength recorded is noted, with specific conditions leading to breakdown outlined.

1. HIGH VOLTAGE
ENGINEERING
INTRINSIC (IONIC)
BREAKDOWN
IN SIMPLE
LAUNGUAGE
LEC # 17
BREAKDOWN
IN SOLIDS

2. 2Prof. Prasant Kumar High Voltage Engineering
INTRINSIC BREAKDOWN OR IONIC BREAKDOWN
When voltages are applied only for short
durations of the order of 10-8 sec the dielectric
strength of a solid dielectric increases very
rapidly to an upper limit called the intrinsic
electric strength.
 The maximum electrical strength recorded is
15 MV/cm for poly vinyl alcohol at - 196˚C.
 Intrinsic breakdown depends upon the
presence of free electrons which are
capable of migration through the lattice of the
dielectric.

3. 3Prof. Prasant Kumar High Voltage Engineering
Types of Intrinsic Breakdown:
INTRINSIC BREAKDOWN OR IONIC BREAKDOWN
Avalanche
or
Streamer
Breakdown
Electronic
Breakdown

4. 4Prof. Prasant Kumar High Voltage Engineering
Electronic Breakdown
 Intrinsic breakdown occurs in time of the order
of 10-8 sec and therefore is assumed to be
electronic in nature.
 When an electric field is applied, electrons gain
energy from the electric field and cross the
forbidden energy gap from the valence to the
conduction band.
 When this process proceeds continuously, more
and more electrons get collected in conduction
band, and it leads breakdown.
INTRINSIC BREAKDOWN OR IONIC BREAKDOWN

5. 5Prof. Prasant Kumar High Voltage Engineering
Avalanche or Streamer Breakdown
 This is similar to breakdown in gases
due to cumulative ionization.
 Conduction electrons gain sufficient
energy above a certain critical electric
field and cause liberation of electrons
from the lattice atoms by collisions.
 Under uniform field conditions, if the
electrodes are embedded in the
specimen, breakdown will occur when
an electron avalanche bridges the
electrode gap.
INTRINSIC BREAKDOWN OR IONIC BREAKDOWN

6. 6Prof. Prasant Kumar High Voltage Engineering