The document presents an overview of sulfur hexafluoride (SF6) circuit breakers, including their types based on voltage applications, operating principles, advantages, and disadvantages. SF6 circuit breakers excel in interrupting high electric currents due to the gas's excellent arc-quenching properties and insulation ability, making them suitable for high-voltage applications. However, they are costly and require reconditioning after operation, limiting their widespread adoption.

1. A
PRESENTATION
ON
SF6 CIRCUIT BREAKER
BY
PURSHOTTAM SUMAN
K-11238
B-TECH, ELECTRICAL

2. INTRODUCTION
 Sulfur hexafluoride circuit breakers protect
electrical power stations and distribution
systems by interrupting electric currents, when
tripped by a protective relay.
The attachment of electron with SF6 gas
molecules may occur in two different ways,

3. TYPES
There are mainly three types of SF6 CB depending
upon the voltage level of application-
 Single interrupter SF6 CB applied for up to 245 KV
system.
 Two interrupter SF6 CB applied for up to 420 KV
system.
 Four interrupter SF6 CB applied for up to 800 KV
system.

4. …

5. Operating principle
 Current interruption in a high-voltage circuit breaker is obtained by
separating two contacts in a medium, such as sulfur
hexafluoride(SF6), having excellent dielectric and arc-quenching
properties. After contact separation, current is carried through an arc
and is interrupted when this arc is cooled by a gas blast of sufficient
intensity.
 The SF6 is an electronegative gas and has a strong tendency to
absorb free electrons.
 The contacts of the breaker are opened in a high pressure flow of
SF6 gas and an arc is struck between them.
 The gas captures the conducting free electrons in the arc to form
relatively immobile negative ions. This loss of conducting electrons
in the arc quickly builds up enough insulation strength to extinguish
the arc.

6. …
 A gas blast applied to the arc must be able to cool it
rapidly so that gas temperature between the contacts is
reduced from 20,000 K to less than 2000 K in a few
hundred microseconds, so that it is able to withstand
the transient recovery voltage that is applied across the
contacts after current interruption.
 SF6 is generally used in present high-voltage circuit
breakers at rated voltage higher than 52 kV.

7. Advantages
 Due to the superior arc quenching property of SF6, such
circuit breakers have very short arcing time.
 the dielectric strength of SF6 gas is 2 to 3 times that of
air, such breakers can interrupt much larger currents.
 There is no risk of fire in such breakers because SF6 gas
is non-inflammable.
 There are no carbon deposits so that tracking and
insulation problems are eliminated.

8. ….
 The SF6 breakers have low maintenance cost,
light foundation requirements and minimum
auxiliary equipment.
 SF6 breakers are totally enclosed and sealed
from atmosphere, they are particularly suitable
where explosion hazard exists.

9. Disadvantages
 SF6 breakers are costly due to the
high cost of SF6.
 SF6 gas has to be reconditioned after
every operation of the breaker,
additional equipment is required for
this purpose.

10. Applications
 A typical SF6 circuit breaker consists of interrupter
units each capable of dealing with currents up-to 60 kA
and voltages in the range of 50—80 kV.
 A number of units are connected in series according to
the system voltage.
 SF6 circuit breakers have been developed for voltages
115 kV to 230 kV,
 power ratings 10 MVA to 20 MVA and interrupting time
less than 3 cycles.