doble TDR9000, User Manual, Page: 208 / 454

Interruption in Oil
A-8 72A-1898 Rev. A 11/01
Monday
, November 26, 2001 1:09 pm
Interruption in Oil
The heart of the circuit breaker is the arc control device. This device
brings about a condition, at the earliest instance when the current is zero
after contact separation, where the path of the resulting arc
loses its
memory concerning its conducting state.
Figure A.7 shows the crossblast interrupter method, where the arc is
drawn in front of a series of lateral vents. The heat of the arc vaporizes
the oil, and the gases formed (mainly hydrogen) increase in pressure and
force the arc to bow into the vents. Before the arc can escape from the
vents, it short circuits itself at the entry point to the vents.
Figure A.7 Circuit Breaker Interruption in Oil
This process continues throughout the arcing period at intervals of the
order of tens of microseconds, though these time intervals are not
constant because the relevant events both inside and outside the arc
control device are changing continuously.
Ultimately, when the pressure inside the arc control device becomes
sufficiently high, and the length of the arc is also sufficiently extended at
a power frequency of current zero, the arc is extinguished.
The arc always burns inside a bubble of gas, and this bubble extends and
expands through the vents to the outside of the arc control device. The
hot gases emerging from the vents are initially still ionized and it is
essential to ensure by correct vent design that no breakdowns occur
between the vents external to the arc control device. This is particularly
important for EHV interrupters where multiple series vent arrangements
are invariably used.
Oil circuit breakers are used up to 345 kV.