Circuit Breakers
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Transcript Circuit Breakers
Circuit Breakers
Definition
Device designed to open the circuit
automatically under abnormal conditions
without damage to itself when properly
applied within its rating.
Circuit breakers are categorized by the
method employed to interrupt the circuit
current (extinguishing the arc) when the
current contacts open.
Four major types
Air
Oil
Vacuum
Gas (SF6 or SF6/CF4)
Two methods circuit breakers sense
circuit current
Thermal
Magnetic
Thermal circuit breaker
Sense circuit current through the production
of heat
Generally uses some type of heating
element in series with the load
The heater is located close to a bimetallic
strip
The bimetallic strip is mechanically
connected to the moveable contacts
Thermal circuit breaker
There is a time delay before the circuit
opens
The time delay depends on the amount of
overcurrent
Thermal Circuit Breaker
Schematic symbol
Schematic
Magnetic circuit breaker
Also known as Instantaneous trip circuit
breaker
Senses circuit current by connecting a coil in
series with the load
When current flows thought the circuit, a
magnetic field is established around the coil
The magnetic field attracts the metal arm of
a solenoid
Magnetic circuit breaker
When the magnetic field becomes intense
enough the metal arm mechanically opens
the contacts
There is very little time delay in opening the
contacts when an abnormal condition
occurs
Magnetic Circuit Breaker
Schematic symbol
Schematic
Thermomagnetic circuit breaker
Most common type
Schematic symbol
Employs both thermal and magnetic current
sensors
Four Major Types
Air
Oil
Vacuum
Gas (SF6 or SF6/CF4)
Air circuit breaker
Divided into four basic types
1 Moulded Case CB (120V – 750V)
2 Low-Voltage Power CB (120V – 750V)
3 Medium-Voltage CB (1.5kV – 69kV)
4 High-Voltage CB (115kV – 230kV)