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. OPERATING PRINCIPLE
Two contacts called FIXED CONTACT and MOVING CONTACT
remains closed under normal operating conditions..
the contacts are engaged each other under the pressure of a spring.
When fault occurs on any part of the
system, the trip coil of the circuit breaker get
energized and contacts are separated..
4. During the normal operating condition, the armsofthe circuit
breaker canbe opened or closed fora switching and maintenance
ofthe system. To open thecircuit breaker, only a pressureis
required to be applied to a trigger.
Whenevera fault occurson anypart ofthe system, thetrip coil of
the breaker gets energized and themoving contacts are getting
apart from each otherby some mechanism, thusopening the
circuit
T
5. During the separation of contact due to large fault
current or high current density at the contact region
the surrounding medium ionizes and thus a
contacting medium is formed ,this is called ARC..
The arc provides the low resistance path to the
current and the current in the circuit remains
uninterrupted…
f
ARC
MOVING
CONTACT
FIXED
CONTACT
ARC PHENOMENON
6. ::THERE ARE TWO METHOD OF ARC EXTINCTION IN CIRCUIT BREAKER ::
HIGH RESISTANCE METHOD-- In this method we increased
the resistance with time ,so that the current is reduced to such a value
that heat is formed by this is not sufficient to maintain the arc or thus arc
is extinguished ..
This can be used in low power AC & DC circuit breaking..
METHOD ARE-
Cooling arc.
Increasing the length of arc.
Reducing the cross-section area of the arc.
Splitting the arc.
7. LOW RESISTANCE METHOD OR ZERO CURRENT
INTERVAL METHOD :–
This method is only applicable only in ac circuit
interruption because there are natural zero of
current 100 times in a second for 50 Hz supply ‘
Arc resistance is kept low until current zero, where
the arc extinguishes naturally and is prevented from
restriking in spite of the rising voltage across the
contacts.
8. The real problem in A.C interruption is to
rapidly deionized the medium between contacts as
soon as the current become zero so that the rising
contact voltage or restriking voltage can't
breakdown the space between contacts , the de-
ionzation of the medium can be achieved by ….
Lengthening of the gap.
High pressure
Cooling
Blast effect.
9. Circuit breakers mainly are categorized based
on application as per voltage:
LOW VOLTAGE CIRCUIT BREAKER
• MCB (MINIATURE CIRCUIT BREAKER)
• MCCB (Molded Case Circuit Breakers)
• ACB ( AIR CIRCUIT BREAKER)
• MPCB(MOTOR PROTECTION CIRCUIT BREAKER)
• RCBO(Residual Current Breaker with Over-
Current)
• RCCB(Residual Current circuit Breaker )
10. MCB or Miniature Circuit Breaker is a
circuit breaker which is used for
protection where current ratings are
lower. It can be used up to 125A circuits
& it also offers protection against
overload & short circuit through bimetal
& solenoid.
These days Class 3 MCBs are very
popular due to their ability of tripping
quickly & also minimum loss of let
through energy.
MINIATURE CIRCUIT BREAKER
11. MCCB (Molded Case Circuit Breaker)
o MCCB OR MOLDED CASE CIRCUIT
BREAKER is a kind of circuit breaker which
is enclosed in the molding or housing of a
molded material & that is the reason it is
known as Molded Case Circuit Breaker.
o It is generally used for the current ratings
up to 1600A & fault level up to 150KA.
o It offers protection against overload &
short circuits through bimetal & solenoid,
these days Microprocessor based MCCBs
are being very popular due to the quick
functioning of their electronic type release.
12. o AIR CIRCUIT BREAKER or ACB
as the name suggests it’s the
circuit breaker where the
medium of arc quenching is air.
ACB is used for the high current
applications, or we can say that
ACB can offer protection against
overload & short circuit up to
6300A.
o Tripping in ACB is achieved
through release. The release is
known as the mind of ACB as it
only suggests the ACB to trip in
AIR CIRCUIT
BREAKER
13. MPCBs are used specially
for motor
protections. MPCB as a
standalone device offers
protection against
Overload, Short Circuit &
Single Phasing, thus is
used specifically for motor
applications.
MOTOR PROTECTION CIRCUIT BREAKER
(MPCB)
14. RCCBs as the name suggests offer
protection against Earth Leakage.
o It is used in homes, offices &
industries according to the current
sensitivity required as per
application.
o In case of current leakage, it
senses the same & trips thus,
saving the human & circuit from
shock & adverse effects of current
leakage.
RESIDUAL CURRENT CIRCUIT BREAKER
(RCCB)
15. o RCBOs are commonly used
in applications where there is the
need to combine protection
against overcurrents (overload
and short-circuit) and protection
against earth leakage currents.
o RCBOs help in sensing this kind
of faults and trip the circuit
ensuring complete protection of
the people and connected
equipment
Residual Current Breaker with Over-Current
16. High Voltage Circuit Breakers
Voltage level from 1KV-69KV IS CATEGORIZED UNDER
MEDIUM & 69KV-230KV IS CATEGORIZED AS HIGH
VOLTAGE.
Circuit Breakers operating in these voltage ranges are known
as Medium & High Voltage CBs respectively.
•VCB(vacuum circuit breaker)
•OCB(oil circuit breaker)
•ABCB(air blast circuit breaker)
•SF6(sulphur-hexafloride circuit breaker)
17. VCB(vacuum circuit
breaker)
Vacuum Circuit Breaker or VCB is used for Medium
Voltage applications. In VCB the contacts operation &
arc quenching takes place inside bottles where Vacuum
is present.
Vacuum offers the highest insulating strength. So it has
far superior arc quenching properties than any other
medium.
• (630A- 1,250A) rated current
Advantages-
• Compact, reliable and have longer life.
• No fire hazards.
• No generation of gas during and after operation.
• Can interrupt any fault current.
• No noise is produced while operating.
• Require less power for control operation
18. In OIL CIRCUIT BREAKER oil is used, but mineral oil is
preferable. It acts better insulating property than air. The
moving contact and fixed contact are immersed inside the
insulating oil.
When the separation of current takes place, then carrier
contacts in the oil, the arc in the circuit breaker is initialized
at the moment of separation of contacts, and because of
this arc in the oil is vaporized and decomposed in hydrogen
gas and finally creates a hydrogen bubble around the arc.
This highly compressed gas bubble around and arc
prevents re-striking of the arc after the current reaches zero
crossings of the cycle.
The OCB is the oldest type of circuit breaker.
The rating range of oil circuit breaker lies from 25MVA at
2.5KV to 5000 MVA at 230KV
OCB(oil circuit breaker)
19. Air blast circuit breaker used compressed air or
gas as the arc interrupting medium. In the air blast,
circuit breaker compressed air is stored in a tank
and released through a nozzle to produce a high-
velocity jet; this is used to extinguish the arc. Air
blast circuit breakers are used for indoor services
in the medium high voltage field and medium
rupturing capacity.Generally up to voltages of 15
KV and rupturing capacities of 2500 MVA. The air
blast circuit breaker is now employed in high
voltage circuits in the outdoors switch yard for 220
KV lines.
Air Blast Circuit
Breaker
20. Sulphur Hexafluoride (SF6) gas is used as
an arc quenching medium.
SF6 is an electro-negative gas.
It has strong tendency to absorb
electrons.
When contact are opened in a high-
pressure flow of SF6 gas, arc produced.
Free electron in the arc are captured by
the gas.
Which build up enough insulation
strength to extinguish arc.
it is much effective for high power and
high voltages services,
These circuit breakers are available for the
voltage ranges from 33KV to 800 KV and
even more.
SF6 CIRCUIT BREAKER
