2 OHB outdoor circuit-breaker Fields of applicationoutdoor installationscontrol and protection of distribution linescontrol and protection of distribution substationscontrol and protection of transformerscontrol and protection of capacitor banks
3 OHB outdoor circuit-breaker Electrical characteristicsRated voltage kVWithstand voltage (1 min.) 70 (60) 95 (80) kV dry (wet)Impulse withstand voltage kVRated normal current at 40°C / ARated frequency / 60 HzRated breaking capacity / kAMaking capacity / 80 kAOperating temperature °C
4 OHB outdoor circuit-breaker StandardsIEC (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 STDs as for Environmental Management SystemISO 9001 STDs as for Quality Assurance System
6 OHB outdoor circuit-breaker FeaturesThree Phase Circuit BreakerThe same arcing chamber of HD4 MV indoor c.b. seriesHD4 arcing chamber housed in a hollow porcelain cylinderCeramic insulators assembled by means of flanges with terminalsPole cap, flanges, sump in anodized alluminium alloyPole ”sealed for life” pressure systemPole cover with safety valveTerminal for connection as NEMA 4 form
7 OHB outdoor circuit-breaker FeaturesESH 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 controlsComplete range of accessoriesWide range of power supply voltages of the electrical accessoriesTwo-levels pressure-switchCabinet housing all the actuator, the control devices, the operating shafts and lever, the transmission, the poles linkage
8 OHB outdoor circuit-breaker FeaturesCabinet supporting the three pole assembliesCabinet and cabinet supporting structure made of hot galvanised steel sheetWeather proof cabinetTight door with window for status c.b. inspection without opening the cabinet doorCase door handle suitable for three padlocksAnti-condensation heater and heating elements for low temperature
9 OHB outdoor circuit-breaker FeaturesCT brackets (on request)”Closed”, ”Open”, ”Spring charged/discharged”, ”SF6 low pressure” signalling lamps (on request)Particularly sturdy constructionSimple structure requiring minimal preparation of the siteMounting arrangementsCabinet 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 techniqueLow operating energy thanks to the ”autopuffer” techniqueMinimal maintenanceLife in excess of 10,000 mechanical operationsSeparation between main and arcing contacts ensuring no wear of the main contactsLife in excess of 10,000 electrical operations at rated current
11 OHB outdoor circuit-breaker SF6 interrupterLow filling pressure respect to a pure puffer techniqueArcing-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
13 OHB outdoor circuit-breaker Breaking techniqueM.V. quenching technique based on proven advantages of SF6 ”auto-puffer” H.V. circuit-breaker well-known, tested and used in the major industrialized countriesState-of-the-art SF6 breaking technology
14 OHB outdoor circuit-breaker Autopuffer quenching technique : interruption processCloseOpening of the main contactsOpening of the arcing contactsOpen
15 OHB outdoor circuit-breaker The circuit-breaker is closedUpper terminalNozzleMain contactsArcing contactsThe 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 contact2) no leakage from the cylinder of the moving arcing contact as it is blocked by the fixed arcing contact3) 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 contact5) 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 contactsThe 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 positionThe 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.