20%) and ultimately result in to the insulation fail-
ure Several theories have been proposed to explain
the breakdown mechanism in liquid dielectrics. For
case study two different mechanisms will be dis-
cussed here;
a. Cavitation or Bubble Mechanism
b. Suspended Particle Mechanism
(a) Cavitation or Bubble Mechanism:
Gas bubbles may produce in liquid dielectrics due
to the vaporization of liquid by corona-type dis-
charges from sharp points/irregularities on the
electrode surfaces or inclusion of moisture from air
through transformer breather producing water bub-
bles in the liquids. Irrespective of the type of mech-
anism, once a cavity or bubble is formed in the liq-
uid dielectrics, it will be elongated in the direction
of electric field due to applied voltage and gradually
bridges the gap in transformer tank resulting in to
the subsequent breakdown as shown in the
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