OHB O utdoor sulphur H exafluoride circuit- B reaker

1. OHBOutdoorsulphur Hexafluoride circuit-Breaker 1-2002

2. OHB outdoor circuit-breaker • Fields of application • outdoor installations • control and protection of distribution lines • control and protection of distribution substations • control and protection of transformers • control and protection of capacitor banks

3. OHB outdoor circuit-breaker • Electrical characteristics • Rated voltage 24 36 kV • Withstand voltage (1 min.) 70 (60) 95 (80) kV dry (wet) • Impulse withstand voltage 150 200 kV • Rated normal current at 40°C 1250 / 2500 A • Rated frequency 50 / 60 Hz • Rated breaking capacity 25 / 31.5 kA • Making capacity 63 / 80 kA • Operating temperature -30 . . . . + 40 °C

4. OHB outdoor circuit-breaker • Standards • IEC 60056 (tested in compliance with the prescriptions of Amendment 3, table XII, list 1 in order to ensure suitability for overhead lines with rapid re-closing cycle) • IEC 60694

5. OHB outdoor circuit-breaker • Development, production, quality control according to : • ISO 14001 STDs as for Environmental Management System • ISO 9001 STDs as for Quality Assurance System

6. OHB outdoor circuit-breaker • Features • Three Phase Circuit Breaker • The same arcing chamber of HD4 MV indoor c.b. series • HD4 arcing chamber housed in a hollow porcelain cylinder • Ceramic insulators assembled by means of flanges with terminals • Pole cap, flanges, sump in anodized alluminium alloy • Pole ”sealed for life” pressure system • Pole cover with safety valve • Terminal for connection as NEMA 4 form

7. OHB outdoor circuit-breaker • Features • ESH spring charged operating mechanism (the same actuator of the whole the HD4 series) • Mechanical anti-pumping device to prevent re-closing due to both electrical and mechanical controls • Complete range of accessories • Wide range of power supply voltages of the electrical accessories • Two-levels pressure-switch • Cabinet housing all the actuator, the control devices, the operating shafts and lever, the transmission, the poles linkage

8. OHB outdoor circuit-breaker • Features • Cabinet supporting the three pole assemblies • Cabinet and cabinet supporting structure made of hot galvanised steel sheet • Weather proof cabinet • Tight door with window for status c.b. inspection without opening the cabinet door • Case door handle suitable for three padlocks • Anti-condensation heater and heating elements for low temperature

9. OHB outdoor circuit-breaker • Features • CT brackets (on request) • ”Closed”, ”Open”, ”Spring charged/discharged”, ”SF6 low pressure” signalling lamps (on request) • Particularly sturdy construction • Simple structure requiring minimal preparation of the site • Mounting arrangements • Cabinet supported by telescopic supports with adjustable height from 2916 up to 3676 mm (structure in compliance with the prescription of BS 7354 STDs) • Cabinet at ground level

10. OHB outdoor circuit-breaker • SF6 interrupter • ”Autopuffer” technique based on compression and self-blast technique • Low operating energy thanks to the ”autopuffer” technique • Minimal maintenance • Life in excess of 10,000 mechanical operations • Separation between main and arcing contacts ensuring no wear of the main contacts • Life in excess of 10,000 electrical operations at rated current

11. OHB outdoor circuit-breaker • SF6 interrupter • Low filling pressure respect to a pure puffer technique • Arcing-chamber common to HD4 series (tested arcing-chamber) • Pole assembly / ceramic insulators similar to the previous SFE series (tested solution) • Monitoring of the quenching media ”SF6” thanks to the pressure switch

12. OHB outdoor circuit-breaker 1 Terminal 2 Insulating enclosure 3 Blasting nozzle 4 Moving arcing contact 5 Moving contact 6 Fixed arcing contact 7 Fixed contact 8 Insulating tie-rod 9 Cap with bursting valve

13. OHB outdoor circuit-breaker • Breaking technique • M.V. quenching technique based on proven advantages of SF6 ”auto-puffer” H.V. circuit-breaker well-known, tested and used in the major industrialized countries • State-of-the-art SF6 breaking technology

14. OHB outdoor circuit-breaker Autopuffer quenching technique : interruption process Close Opening of the main contacts Opening of the arcing contacts Open

15. OHB outdoor circuit-breaker The circuit-breaker is closed Upper terminal Nozzle Main contacts Arcing contacts The current flows from the upper (fixed) terminal to the moving part through the main contacts. Moving part

16. OHB outdoor circuit-breaker Opening of the main contacts. The moving part goes down thus separating the main contacts. There is no arc striking as the current keeps flowing from the upper terminal to the moving parts through the arcing contacts. During the downstroke, the moving part exert a pressure on the gas housed in the lower chamber; the pressure increase generated in the lower chamber opens the connection valve of the upper chamber. The compressed gas flows from the lower to the upper chamber thus taking both enclosures at the same pressure level.

17. OHB outdoor circuit-breaker Notes: 1) no leakage from the nozzle as it is blocked by the fixed arcing contact 2) no leakage from the cylinder of the moving arcing contact as it is blocked by the fixed arcing contact 3) the upper chamber is connected to the moving mechanism and its volume remains the same during the downstroke (dead volume) 4) the only changing volume is the one of the lower chamber, which decreases during the downstroke of the moving contact 5) this puffer is designed to avoid chopping currents by means of a “dead volume” higher than the compressed volume. As the gas flows towards the upper chamber, the pressure level is equal to the ratio between the dead volume and the lower chamber volume.

18. OHB outdoor circuit-breaker Opening of the arcing contacts The current keeps flowing due to the arc generated between the fixed and moving contacts. The gas cannot leak either from the nozzle as the hole is blocked by the fixed contact or from the inside of the moving contact because of the arc clogging effect.

19. OHB outdoor circuit-breaker The breaking chamber undergoes the following process: at low currents: as the current hits the natural zero and the arc is quenched, the gas flows from the dead volume to the inside of the moving contact. The low pressure guarantees the absence of chopping currents and the small quantity of gas involved is sufficient to restore the dielectric strenght between the two contacts by avoiding, at the same time, the re-strike of the transient recovery voltage.

20. OHB outdoor circuit-breaker At higher short circuit currents: the pressure wave of the arc propagates like a supersonic wave, increasing the gas pressure which closes the valve between the two chambers. From this moment on, the device starts working as a pure “self-blast”, the gas overheating and the molecular dissociation due to the high temperature increase the pressure in the dead volume. Said pressure is proportional to the arc and the resulting gas flow guarantees the quenching at the first passage through zero natural current.

21. OHB outdoor circuit-breaker Circuit-breaker in the open position The arc is quenched; the lower chamber reaches its minimum volume and its maximum pressure level, kept by the valve locked by the supersonic wave. As the self-generated pressure of the dead volume decreases, due to the outflow of the gas through the moving contact, the valve re-opens. From now on, a new jet of fresh gas flows in and makes the temperature of the contacts sink. At the same time, the gas flows through the nozzle, free from the fixed arcing contact. The “cleaning” of the arcing chamber by means of fresh gas makes the device suitable for another reclosing and the interruption up to the maximum breaking capacity.