Presentation on theme: "WHAT IS A CIRCUIT BREAKER"— Presentation transcript:
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 deviceCommanding deviceActuating device
4 EXAMPLES OF EACH OF THE FOLLOWING SEQUENCE OF OPERATION SENSING COMMANDINGCurrent transformer (CT) Overcurrent relayPotential transformer (PT) Over Voltage relayThermal device (thermocouple) Temperature relayGas relays (Buchholz) Gas relay-86G
5 cont. EXAMPLES OF EACH OF THE FOLLOWING SEQUENCE OF OPERATION ACTUATING DEVICECircuit Breaker
6 PHOTOS OF SEQUENCE OF OPERATION SENSING DEVICECURRENT TRANSFORMER (CT) THERMOCOUPLE
7 Cont. PHOTOS OF SEQUENCE OF OPERATION COMMANDING DEVICEOVER 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 DEVICECircuit Breaker (CB) LIVE TANK
10 TYPES OF CIRCUIT BREAKER The type of a circuit breaker is derived from it’s quenching mediumQUENCHING MEDIUM BREAKER TYPEOil OIL CIRCUIT BREAKER (OCB)Vacuum VACCUM BREAKERSF6 Gas SF6
15 INTERRUPTING CHAMBERThis is the name given to the chamber housing the contacts. There are two types of Interrupters (CB)Live tankDead tankThe 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.
21 PROPERTIES OF SULFUR HEXAFLUORIDE (SF6) GAS Heavy, chemically inert, non toxicNo poisonous effect on the human body but decomposition products are poisonousColorless and odorlessIt is gaseous at normal room temperature and pressureDensity 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 compressionVery 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 stableUnlike solid insulation materials, electrical breakdown of SF6 gas does not result in permanent deterioration of its propertiesDecomposition 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 odorlessFive times heavier than airTemperature-resistant up to 500 degrees CelsiusChemically stableNon-toxicNon-inflammableExcellent dielectric properties