Vacuum circuit breakers use vacuum to extinguish the arc when opening contacts. They have fixed contacts, moving contacts, and an arc shield mounted inside a vacuum chamber. When a fault is detected, the contacts separate and the arc is quickly extinguished in the vacuum. This allows vacuum circuit breakers to reliably interrupt high fault currents. They have advantages over other circuit breakers like being compact, reliable, and able to interrupt heavy fault currents without fire hazards.

1. VACUUM CIRCUIT
BREAKER

2. WHAT IS A CIRCUIT
BREAKER

A circuit breaker is an
equipment that breaks a
circuit either manually or
automatically under all
conditions at no load,
full load or short circuit.

3. VACUUM CIRCUIT
BREAKERS

A Vacuum circuit breaker is
a circuit breaker in which
vacuum is used to extinct
the arc. VCB have excellent
interruption and dielectric
recovery characteristics,
and can interrupt the high
frequency currents which
result from arc instability,
superimposed on the line
frequency current.

4. CONSTRUCTION OF
VCB
The main parts of a typical
VCB are Fixed contact
 Moving contact
 Arc shield
Which are mounted
inside a vacuum
chamber.

5. CONSTRUCTION OF
VCB




The fixed contact is a permanent contact
provided in the VCB between the insulator
support and pole terminal.
The moving support is provided between the
insulator and metallic bellow.
The movable member is connected to the
control mechanism by stainless steel bellows.
This enables the permanent sealing of the
vacuum chamber so as to eliminate the
possibility of leak.

6. CONSTRUCTION OF
VCB


A glass vessel or ceramic
vessel is used as the outer
insulating body.
The arc shield prevents the
deterioration of the internal
dielectric strength by
preventing metallic vapors
falling on the inside surface
of the outer insulating
cover.

7. PRINCIPLE OF
OPERATION

Two contacts called
electrode remains
closed under normal
operating conditions.
When fault occurs on
any part of the
system, the trip coil
of the circuit breaker
gets energized and
contacts are
separated.

8. PRINCIPLE OF
OPERATION


When the contacts of the breaker are
opened in vacuum (10-7 to 10 -5 torr), an
arc is produced between the contacts by the
ionization of metal vapors of contacts.
The arc is quickly extinguished because the
metallic vapors, electrons and ions
produced during arc condense quickly on
the surfaces of the circuit breaker contacts,
resulting in quick recovery of dielectric
strength.

9. WORKING
The circuit breaker are essential as isolator cannot be
used to open a circuit under normal conditions as it
has no provision to quench arc that is produced after
opening the line. It has to perform following function
Full load current is to be carried continuously

Opening and closing the circuit on no load

Making and breaking the normal operating
current

Making and breaking the fault currents of
magnitude up to which it is designed for.

10. WORKING


Arc extinction is the main process of a
circuit breaker. We know that circuit
breakers work under the instructions from
relay.
When the trip coils from relay energize,
circuit breaker identifies fault occurred and
hence the contacts are pulled apart. A high
intensity current flows through the contacts
of the circuit breaker before they are opened
by the system.

11. WORKING

VCBs are capable of
interrupting currents
with a very high (di/dt),
typically in the range of
150 - 1000A/μs and
consequently the highfrequency current may
be interrupted during
one of the high
frequency excursions
through zero. This is
known as virtual
current chopping.

12. ADVANTAGES OF VCB




They are compact, reliable
and have longer life.
There are no fire hazards.
They can interrupt any
fault current.
The outstanding feature of
a VCB is that it can break
any heavy

13. ADVANTAGES OF VCB




Low inertia and hence
require smaller power
for control operation.
No noise is produced
while operating.
Require less power
for control operation.
It has higher dielectric
strength.

14. CONCLUSION


Thus, a circuit breaker is equipment that breaks
a circuit either manually or automatically under
all conditions at no load, full load or short circuit.
Hence, we can say that Vacuum circuit breaker
is really the most reliable one with low cost, no
fire hazards, no gas generation, low arc energy,
little maintenance and low inertia. So this is the
most widely used circuit breaker used for high
voltage transmission.

15. THANK YOU