FUNDAMENTAL TRAINING ON CIRCUIT BREAKERS PRESENTATION BY: SAMUEL OFFEI-NTOW
Dec 18, 2015
FUNDAMENTAL TRAINING ON CIRCUIT
BREAKERSPRESENTATION 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 COMMANDING• Current transformer (CT) 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 OPERATIONCOMMANDING DEVICE
OVER VOLTAGE OVER TEMPERATURE
Cont. PHOTOS OF SEQUENCE OF OPERATIONACTUATING DEVICECircuit Breaker (CB) DEAD TANK
Cont. PHOTOS OF SEQUENCE OF OPERATION
ACTUATING DEVICECircuit Breaker (CB) LIVE TANK
TYPES OF CIRCUIT BREAKER
The type of a circuit breaker is derived from it’s quenching medium
QUENCHING MEDIUM BREAKER TYPE• Oil OIL CIRCUIT BREAKER (OCB)• Vacuum VACCUM BREAKER• SF6 Gas 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 MaintenanceModels
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