1. FUNDAMENTAL TRAINING ON CIRCUIT BREAKERS PRESENTATION BY: SAMUEL OFFEI-NTOW

2. 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.

3. SEQUENCE OF OPERATION OF A CIRCUIT BREAKER (CB)
Sensing device
Commanding device
Actuating device

4. 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

5. cont. EXAMPLES OF EACH OF THE FOLLOWING SEQUENCE OF OPERATION
ACTUATING DEVICE
Circuit Breaker

6. PHOTOS OF SEQUENCE OF OPERATION
SENSING DEVICE
CURRENT TRANSFORMER (CT) THERMOCOUPLE

7. Cont. PHOTOS OF SEQUENCE OF OPERATION
COMMANDING DEVICE
OVER VOLTAGE OVER TEMPERATURE

8. Cont. PHOTOS OF SEQUENCE OF OPERATION
ACTUATING DEVICE Circuit Breaker (CB) DEAD TANK

9. Cont. PHOTOS OF SEQUENCE OF OPERATION
ACTUATING DEVICE
Circuit Breaker (CB) LIVE TANK

10. 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

12. Vacuum Circuit Breakers

15. 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.

16. PICTURES OF THE TANKS
LIVE TANK DEAD TANK

17. OPERATING MEDIUM
These are the main operating medium used in Medium and High Voltage Network.
ELECTROMAGNETIC SPRING

18. FKF SPRING MECHANISM FOR AREVA DEAD TANK SF6 CIRCUIT BREAKERS

19. FKF Mechanism Maintenance
Models

20. cont. OPERATING MEDIUM
PNEUMATIC HYDRAULIC

21. 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

22. 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)

23. 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

24. THANK YOU