1. Air Circuit Breaker (ACB)
Principle of Operation:
 Arc Extinguishing Medium: Air.
 How it works: In an air circuit breaker, the arc generated when the contacts open is
extinguished by air. The arc occurs when the electrical contacts of the breaker separate under
fault conditions, and air is used to cool and dissipate the energy of the arc.
 Arc Quenching: The air is blown or forced through the arc to cool it down and help it dissipate,
thus interrupting the current flow. The air itself has to be maintained at sufficient pressure to
quickly cool and quench the arc.
Features:
 Typically used for lower to medium voltages (up to 7.2 kV).
 Air circuit breakers are commonly used in Low Voltage (LV) and Medium Voltage (MV) systems
for distribution and industrial applications.
 They have low interrupting capacities compared to SF6 or vacuum breakers and are less
efficient for high-current interruptions.
 Cost-effective but have higher maintenance requirements.
Advantages:
 Simple construction and relatively inexpensive.
 Suitable for applications in lower-voltage circuits where high interrupting capacity isn't as
critical.
 Can operate in environments with moderate contamination or moisture levels.
Disadvantages:
 Large size compared to vacuum or SF6 breakers.
 Lower interrupting capacity—not suitable for high fault currents (typically up to 10 kA).
 High maintenance due to the wear of contacts and air-blast systems.
2. Vacuum Circuit Breaker (VCB)
Principle of Operation:
 Arc Extinguishing Medium: Vacuum (a low-pressure gas environment inside the breaker).
 How it works: In a vacuum circuit breaker, when the contacts open, the arc occurs in a vacuum.
Since the vacuum is devoid of any gas or material, there are no free electrons available to
maintain the arc. As a result, the arc is rapidly extinguished as soon as it forms.
 Arc Quenching: The vacuum environment provides excellent dielectric properties that prevent
the re-ignition of the arc, ensuring the current is safely interrupted.
Features:
 Primarily used for medium voltage (1 kV to 36 kV) systems.
 Compact and efficient in handling fault currents.
 Fast operation with a very high interrupting speed.
Advantages:
 Compact size: Vacuum breakers are typically smaller and more compact than air circuit breakers
and SF6 circuit breakers.
 Low maintenance: The vacuum medium doesn't degrade over time, so vacuum circuit breakers
require less maintenance than air circuit breakers.
 Efficient arc quenching: Excellent performance in interrupting high fault currents with minimal
wear.
 No need for external gases like air or SF6, which can be cumbersome to manage.
Disadvantages:
 Limited to medium-voltage applications: While very effective at interrupting currents in the
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medium voltage range, they are not typically used for high-voltage systems.
Cost: Vacuum circuit breakers can be more expensive than air circuit breakers.
Not ideal for very high currents: For extremely high fault currents (above 40 kA), vacuum circuit
breakers may struggle, and other technologies (such as SF6) may be preferred.
3. SF6 (Sulfur Hexafluoride) Circuit Breaker
Principle of Operation:
 Arc Extinguishing Medium: SF6 gas (Sulfur Hexafluoride).
 How it works: SF6 circuit breakers use sulfur hexafluoride gas to extinguish the arc when the
contacts separate during fault conditions. SF6 is a highly electronegative gas, meaning it is very
effective at absorbing free electrons and thus quenching the arc. The gas is often pressurized to
enhance its properties.
 Arc Quenching: When the contacts open, an arc forms, but the SF6 gas absorbs the arc's energy,
causing the arc to cool down and extinguish rapidly. The SF6 gas also has excellent insulating
properties, preventing the arc from re-establishing itself.
Features:
 Used in high-voltage systems (36 kV and above), especially in Medium Voltage (MV) and High
Voltage (HV) systems.
 Can interrupt very high fault currents due to the excellent insulating properties of SF6.
 SF6 is pressurized within the breaker to improve its effectiveness in extinguishing arcs and to
handle larger fault currents.
Advantages:
 Very high interrupting capacity: SF6 circuit breakers are capable of interrupting very high fault
currents (up to 100 kA or more).
 Compact size: SF6 circuit breakers are generally smaller and more compact than air-blast
breakers and can handle larger currents with less space.
 Extremely reliable: SF6 is a very stable gas, and the breaker is effective at handling large faults
with minimal wear and tear.
 Low maintenance: SF6 gas doesn't degrade or require frequent replacement, so the
maintenance is minimal, unlike air circuit breakers.
Disadvantages:
 Environmental concerns: SF6 is a potent greenhouse gas, and its use is a subject of
environmental regulation due to its high global warming potential. Efforts are being made to
reduce SF6 emissions and find alternative technologies.
 Cost: SF6 breakers are more expensive than air or vacuum breakers, due to the complexity of
the technology and the pressurized SF6 gas.
 Gas handling: SF6 requires proper handling and disposal procedures to prevent leaks, which can
be costly.
1. SF6 Miniature Circuit Breaker (MCB)
Principle of Operation:
 Arc Extinguishing Medium: SF6 gas (Sulfur Hexafluoride).
 How it works: SF6 miniature circuit breakers work on the same principle as their larger SF6
counterparts but in a more compact, miniature form. SF6 is used as the arc quenching medium
inside the breaker. When a fault occurs, the contacts of the breaker open, and the arc is formed.
The SF6 gas, due to its excellent insulating properties, absorbs the energy of the arc and quickly
extinguishes it, allowing for the interruption of current flow.
Features:
 Size and Application: These are compact, miniature breakers typically used in medium- to high-
voltage circuits (between 12 kV to 36 kV) or for switchgear applications where space is limited.
Interrupting Capacity: Although termed "miniature," these breakers can handle fault currents
similar to standard SF6 circuit breakers but in smaller, more manageable designs for specialized
uses, especially in industrial or power distribution systems.
 Pressurization of SF6 Gas: These breakers are designed to be self-pressurized, or they may use
an external pressurization system depending on the specific application.
Advantages:
 High Interrupting Capacity: Similar to full-sized SF6 breakers, these miniature versions can
interrupt high fault currents, often in the range of 30 kA to 50 kA or more.
 Compact and Space-saving: Their smaller size makes them suitable for use in space-constrained
environments like compact switchgear panels or places where larger breakers would be
impractical.
 Reliability: SF6 gas provides excellent dielectric strength, making the breaker reliable even in
demanding environments.
 Low Maintenance: Like larger SF6 breakers, SF6 miniature circuit breakers require minimal
maintenance since the SF6 gas does not degrade over time.
Disadvantages:
 Environmental Impact: SF6, being a potent greenhouse gas, raises environmental concerns. Its
use is subject to regulation, and alternative solutions are being sought.
 Cost: These breakers are costlier than other types like vacuum or air breakers, primarily due to
the use of SF6 and the complexity of their design.
Typical Applications:
 Medium-Voltage Power Distribution systems where space is limited, such as in compact
substations or industrial switchgear.
 Protection for transformers, generators, and other electrical equipment in medium-voltage
circuits.
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2. Earth Leakage Circuit Breaker (ELCB)
Principle of Operation:
 Arc Extinguishing Medium: Standard arc quenching, typically air or oil, depending on the ELCB
type.
 How it works: An Earth Leakage Circuit Breaker (ELCB) is a safety device used to detect leakage
currents in an electrical system, especially the currents that flow to the earth due to insulation
failure or other faults. The primary function of an ELCB is to protect humans from electric
shocks by detecting leakage current and automatically disconnecting the power supply.
There are two main types of ELCBs:
1. Voltage Operated ELCB (Old Type):
o This type detects earth voltage (potential difference between earth and live conductors)
caused by leakage. It activates when the voltage difference exceeds a threshold,
indicating a leakage of current through the earth.
2. Current Operated ELCB (New Type, more commonly used):
o The more common type today is the Residual Current Circuit Breaker (RCCB), which
detects residual (leakage) currents between live conductors and earth. When there’s an
imbalance in current, such as when current leaks to the ground, the breaker trips and
disconnects the supply. This type is more effective than voltage-operated ELCBs as it
directly senses leakage current.
Features:

Leakage Detection: ELCBs protect against earth faults (like a person coming into contact with a
live conductor, causing leakage to the earth) by detecting residual currents.
 Operation Mechanism: When the leakage current exceeds a specified threshold (typically 30 mA
to 300 mA, depending on the sensitivity), the ELCB trips and disconnects the circuit.
 Protection Function: ELCBs are crucial for personal safety, as they prevent electric shocks from
faults like faulty wiring, equipment failure, or damaged insulation.
Advantages:
 High Sensitivity: ELCBs (especially RCCBs) can detect small leakage currents and quickly
disconnect the power to avoid harm.
 Enhanced Safety: ELCBs are designed to protect people from electric shocks due to insulation
failure or leakage.
 Quick Tripping: The device is very fast in its response time, minimizing the time people are
exposed to leakage current.
Disadvantages:
 Limited to Earth Leakage Faults: ELCBs are not designed to protect against other types of faults,
such as overcurrent or short circuits (unless combined with a MCB or RCCB/MCB).
 Voltage-operated ELCBs have become outdated due to their lower sensitivity and the
introduction of more modern current-operated designs.
 Installation Complexity: Depending on the type (e.g., RCCB), proper installation can be complex,
as it requires a correct neutral-earth connection.
Typical Applications:
 Residential and Commercial Buildings for protection against electric shocks, especially in wet
areas (bathrooms, kitchens) where leakage currents are more likely.
 Industrial Applications to ensure the safety of workers from electric shock hazards due to earth
leakage.
 Substations and Distribution Networks where leakage current could indicate a fault in the
system that may cause safety issues or equipment damage.