FUNDAMENTAL TRAINING ON
CIRCUIT BREAKERS
PRESENTATION BY: SAMUEL OFFEI-NTOW
WHAT IS A CIRCUIT BREAKER
It is a mechanical device used for making and breaking an electric
circuit, both manually and automatically in the event of electric faults.
This definition is basically for domestic application, i.e. Miniature
Circuit Breaker (Low Voltage)
However, in the situation of Medium/High Voltages, there are
additional devices which makes a breaker function perfectly.
SEQUENCE OF OPERATION OF A CIRCUIT
BREAKER (CB)
Sensing device
Commanding device
Actuating device
EXAMPLES OF EACH OF THE FOLLOWING
SEQUENCE OF OPERATION
SENSING
• Current transformer (CT)
COMMANDING
Overcurrent relay
• Potential transformer (PT)
Over Voltage relay
• Thermal device (thermocouple)
Temperature relay
• Gas relays (Buchholz)
Gas relay-86G
cont. EXAMPLES OF EACH OF THE FOLLOWING
SEQUENCE OF OPERATION
ACTUATING DEVICE
• Circuit Breaker
PHOTOS OF SEQUENCE OF OPERATION
• SENSING DEVICE
• CURRENT TRANSFORMER (CT)
THERMOCOUPLE
Cont. PHOTOS OF SEQUENCE OF OPERATION
COMMANDING DEVICE
OVER VOLTAGE
OVER TEMPERATURE
Cont. PHOTOS OF SEQUENCE OF OPERATION
ACTUATING DEVICE
Circuit Breaker (CB) DEAD TANK
Cont. PHOTOS OF SEQUENCE OF OPERATION
ACTUATING DEVICE
Circuit Breaker (CB) LIVE TANK
TYPES OF CIRCUIT BREAKER
The type of a circuit breaker is derived from it’s quenching medium
QUENCHING MEDIUM
• Oil
• Vacuum
• SF6 Gas
BREAKER TYPE
OIL CIRCUIT BREAKER (OCB)
VACCUM BREAKER
SF6
Vacuum Circuit Breakers
INTERRUPTING CHAMBER
• This is the name given to the chamber housing the contacts. There
are two types of Interrupters (CB)
• Live tank
• Dead tank
• The live tank is where the breaking and making action takes place in
an insulated housing.
• Similarly, the dead tank is also housed in a metallic envelope.
PICTURES OF THE TANKS
LIVE TANK
DEAD TANK
OPERATING MEDIUM
• These are the main operating medium used in Medium and High
Voltage Network.
ELECTROMAGNETIC
SPRING
FKF SPRING MECHANISM FOR AREVA DEAD TANK
SF6 CIRCUIT BREAKERS
FKF Mechanism Maintenance
Models
cont. OPERATING MEDIUM
PNEUMATIC
HYDRAULIC
PROPERTIES OF SULFUR HEXAFLUORIDE (SF6)
GAS
• Heavy, chemically inert, non toxic
• No poisonous effect on the human body but decomposition products
are poisonous
• Colorless and odorless
• It is gaseous at normal room temperature and pressure
• Density is about 6.6g/l at 20 degrees Celsius (5 times denser than air)
• Critical temperature is at 45.6 degrees Celsius and can be liquefied by
compression
• Very good insulant with high dielectric strength
Cont. PROPERTIES OF SULFUR HEXAFLUORIDE
(SF6) GAS
• SF6 gas is electo-negative (tends to attract the free electrons and has
the arc quenching property). Because of this main reason SF6 gas is
used for arc quenching and insulation medium in Circuit Breakers.
• The gas is highly stable
• Unlike solid insulation materials, electrical breakdown of SF6 gas does
not result in permanent deterioration of its properties
• Decomposition occurs on the exposure to the electric arc.
(Dissociation products will be SF2 and SF4 order fluorides)
MAJOR PROPERTIES AT A GLANCE
• Colorless and odorless
• Five times heavier than air
• Temperature-resistant up to 500 degrees Celsius
• Chemically stable
• Non-toxic
• Non-inflammable
• Excellent dielectric properties
THANK YOU