It is a general-purpose unit that overcomes the drawbacks of sulphur hexafluoride (SF6) dielectric switches by employing a solid dielectric and patented visible air gap.
NOJA Power's VISI-SWITCH OLB15-16-800 Load Break Switch will be commercially available in early 2017. This switch enables three-phase, medium-voltage distribution network manual isolation. It is a general-purpose unit that overcomes the drawbacks of sulphur hexafluoride (SF6) dielectric switches by employing a solid dielectric and patented visible air gap. The unit also features a unique drive mechanism connecting the vacuum interrupters and isolators which guarantees a safe operational sequence.
NOJA Power has invested $10 million in a new 4300-m2 Manufacturing Campus at its Brisbane headquarters in part to manufacture VISI-SWITCH. The company is planning to hire 50 additional employees and run two shifts per day to cope with anticipated demand for VISI-SWITCH when the units enter full production in 2017.
VISI-SWITCH features a drive mechanism that connects the vacuum interrupters to the isolators and guarantees both parts of the switch will open once operation is initiated. The sequencing of the complete switching operation is dictated by the drive mechanism which rapidly opens the vacuum interrupters to break the current and then, after a short delay, slowly opens the isolators in accordance with the insulation coordination standards. This offers three key advantages over existing solutions: the vacuum interrupters and patent-pending isolators provide load break switching and visible isolation—built into the bushing and observable from the ground when the is mounted on a pole—in a single piece of switchgear that matches the size and weight of existing SF6 three-phase load break switches; the mechanism guarantees a safe operational sequence and sequencing of the vacuum interrupters, and isolators is controlled from a single input ensuring the load break switch is guaranteed to operate.
VISI-SWITCH OLB15-16-800 is manufactured using a stainless steel tank with controlled arc fault venting and employs vacuum interrupters which feature a solid dielectric manufactured from Wacker 310 silicon rubber. This solid dielectric is the same insulating material used in NOJA Power’s OSM series Automatic Circuit Reclosers (ACRs) which have been deployed in over 80 countries around the world. The isolator contact is coated with reflective red paint and can be easily seen through the observation window even at night (with the use of a torch). The window is designed to remain transparent during the entire life of the switch, without any discolouration, is scratch resistant and can withstand extreme temperatures
The switch has a rated maximum voltage of 15.5 kV, a rated continuous current of 800 A and a short time current withstand of 16 kA (for 3 seconds). The switch can operate over a -40 to 55oC temperature range, 0 to 100 percent humidity, and meet specified rating up to a height of 1000 m (and be functional up to 3000 m). The unit is designed to cope with exposure to salt spray, dust, smoke and corrosive gases, vapours and liquids, and can be mounted either horizontally or vertically. Prior to full production VISI-SWITCH will be fully type-tested by independent laboratory KEMA in the Netherlands to ensure long life and reliability under the harshest environmental conditions.
VISI-SWITCH OLB15-16-800 is the first product in NOJA Power’s load break switch family and is a manually-operated device controlled from the ground using either an extended hook stick which reaches directly into the switch or a shorter hook stick that connects to a rod extending from the switch. NOJA Power plans to release a motorised, automated version of VISI-SWITCH which will be controlled from the RC control and communication cubicle – a supervisory system used with the company’s OSM series ACRs. The automated VISI-SWITCH will enable remote operation and sectionaliser functionality. NOJA Power also plans to release 27- and 38-kV versions of the VISI-SWITCH in the near future
Utilities employ three-phase switches to isolate sections of feeders for maintenance work. In recent years, older air gap switches––which could not be operated while the feeder was under load and were unreliable due to environmental exposure––have been replaced by SF6 dielectric switches. Enclosed gas-filled switches can be opened under load due to the arc quenching capabilities of the SF6 and are more reliable because the contacts are protected from weather, pollution and falling objects such as branches.
However, SF6 load break switches suffer from two significant drawbacks: according to the Intergovernmental Panel on Climate Change (IPCC), SF6 is the most potent greenhouse gas that it has evaluated, with a global warming potential of 23,900 times that of CO2, and the enclosed switch makes it impossible for linesmen to visually check if all three phases of the switch have operated before commencing work. NOJA Power has committed significant R&D resource to eliminate these drawbacks and comprehensively updated load break switch design to make VISI-SWITCH OLB15-16-800 the ideal choice for today’s smart grids.