1. CIRCUIT BREAKERS E. Chikuni

2. Circuit Breakers Mechanical Switches capable of making and breaking currents under normal circuit conditions and for a specified time under abnormal conditions, specifically under short circuit conditions. They are designated by the medium in which interruption occurs, e.g. air-blast, oil, vacuum, SF6. They are rated by voltage, insulation level, current, interrupting capacity, transient recovery voltage, interrupting time and trip delay.

3. Brief History Knife Switches. Introduction of Springs for Quicker Action. Arcing Contacts & Main Contacts Arching Chutes

4. Air Circuit Breaker

5. Oil Circuit Breakers Since 1900. Oil very effective medium in quenching. Improvements since include oil blast, deion grid (forcing the arc electromagnetically into a narrow insulated path). OCBs are being used for system voltages up to 330kV

6. Air-Blast Circuit Breakers Since 1940. An oil-less arc, stronger, faster than oil. Air velocity approaching the speed of sound. Can interrupt an arc in 2 cycles (40ms), including the time to energize the trip coil. Indoor ratings up to 38kV, Outdoor up to 800kV Used e.g. generator breakers up to 42 kA & higher, as furnace breaker Continuous ratings up to 4000A Operating pressures up to 25 bar

7. SF6 Circuit Breakers Since 1960. Utilizes the excellent arc quenching and insulating properties of the gas SF6 Dead Tank designs incorporated in GIS substations up to 800kV GIS substations are more compact and environmentally friendly than outdoor substations. Operating pressure about 3 bars

8. SF6 Circuit Breakers Since 1960. Utilizes the excellent arc quenching and insulating properties of the gas SF6 Dead Tank designs incorporated in GIS substations up to 800kV GIS substations are more compact and environmentally friendly than outdoor substations.

9. SF6 Circuit Breakers Several characteristics of SF6 circuit breakers can explain their success: Simplicity of the interrupting chamber which does not need an auxiliary breaking chamber; Autonomy provided by the puffer technique; The possibility to obtain the highest performance, up to 63 kA, with a reduced number of interrupting chambers; Short break time of 2 to 2.5 cycles; High electrical endurance, allowing at least 25 years of operation without reconditioning; Possible compact solutions when used for GIS or hybrid switchgear; Integrated closing resistors or synchronized operations to reduce switching over-voltages; Reliability and availability; Low noise levels.

10. SF6 Breaker Principle

11. SF6 Puffer Principle

13. SF6 Contacts

14. SF6 Installation

15. Vacuum Circuit Breakers More recent development. Used up to 33kV but units for over 220kV service have been constructed. The contacts are built in an evacuated enclosure. During operation a metallic arc forms but is quickly extinguished during an ionic re-combination process. This is attributable to the excellent di- electric properties of vacuum. The time involved is in the order of microseconds.

16. Vacuum Circuit Breaker Construction

17. Example of a MV SF6 CB

18. Application MV overhead distribution Switch: PM6 MV/LV distribution substation Ringmaster RN2 Heavy ind. substation Withdrawable: YSF6 Withdrawable YSF6 Main priority substation Medium priority substation Withdrawable: YSF6 Fixed: GENIE Medium ind. substation Withdrawable: YSF6 Fixed: GENIE Medium ind./comm.substation Fixed indoor: GENIE Fixed outdoor: CE6:CE2/SE6/MU HV/MV 132/33kV 132/11kV MV/MV 132/11kV 11/11kV MV/LV 11kV/415V O/HEAD UTILITYCOMMERCIALINDUSTRY

19. FIXED PORTION Relay Cabinet Busbars Cable box CT’s Circuit Breaker Truck Circuit position

20. FIXED PORTION Relay Cabinet Busbars Cable box CT’s Circuit Breaker Truck Circuit earth position

21. FIXED PORTION Relay Cabinet Busbars Cable box CT’s Additional busbar earthing device Busbar earth position

22. FIXED PORTION Duplicate busbar option Relay Cabinet Upper Busbars Cable box CT’s Relay Cabinet Upper Busbars Cable box CT’s Lower Busbars

23. Voltage transformer Isolateable and fused - reliability Fully interlocked -operator safety Circuit and busbar connected - network flexibility Cast resin design - maintenance free

24. Moving portion Horizontal isolation and withdrawal - ease of operation Technology SF6 puffer - low switching surges 3 phase cast resin moulding with minimum number of seals - proven reliability Low standing gas pressure - integrity Electrical pressure switches - constant monitoring of medium

25. Puffer technique CB open initiation - main contacts separated - overpressure created by piston

26. Puffer technique Arcing contacts separated - Arc struck between arcing contacts - SF6 over pressure forced into nozzle -Arc interrupted at first current zero

27. Puffer technique Circuit Breaker open -Contacts in fully open position - Gas pressure equalised

28. Interrupting medium SF 6 : universal technology Long service life. Switching under difficult conditions. High installation flexibility. Very low maintenance. No surges, smooth breaking. Insensitivity to the environment.

29. Endurance characteristic 1 10 100 1000 10000 100000 10000 2000 1000 100 10 1 Current interrupted (A) Number of operations 20kA 25kA 31.5kA 40kA

30. Cable box Cable entry above & below - installation flexibility Dyscon cable termination's - operator safety Neon circuit indication - low cost voltage presence

31. Busbars Fully encapsulated system - installation reliability High conductivity copper conductors - 1250A, 2500A rated Padlockable shutters - operator safety

32. Construction Metalclad design Compact design. Modular construction. Encapsulated MV system Spring loaded busbar and circuit shutters