T&D World Magazine
Visiswitch

Solid Dielectric Insulation Load Break Switch

VISI-SWITCH features vacuum interrupters with solid dielectric to eliminate environmentally-damaging SF6 gas, unique drive mechanism ensuring safe sequencing and operation, and a visible air isolation gap for maintenance staff safety

NOJA Power has introduced its VISI-SWITCH LBS15-16-800 for three-phase electricity distribution grid feeder manual isolation. The load break switch 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’s VISI-SWITCH employs vacuum interrupters with solid dielectric, 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). NOJA Power plans to release 27- and 38-kV versions of the VISI-SWITCH in the near future.

The 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. This offers three key advantagess: the vacuum interrupters and isolators provide load break switching and visible break isolation 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.

The VISI-SWITCH can operate over a -40 to 55°C 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, vapors and liquids, and can be mounted either horizontally or vertically.

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could not be operated while the feeder was under load and were unreliable due to environmental exposure––have been replaced by sulphur hexafluoride (SF6) dielectric switches.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 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 update load break switch design to make the VISI-SWITCH™ LBS15-16-800 the ideal choice for today’s smart grids.

“While enclosed SF6 gas switches addressed the reliability deficiencies of air gap switches this came at a cost of compromised safety because maintenance staff could no longer visually check that all three phases were isolated before starting work on the feeder,” explains Neil O’Sullivan, NOJA Power’s Managing Director. “This requires a significant leap of faith by electricity utility linesmen and there are many that don’t feel comfortable with enclosed gas switches.

The VISI-SWITCH LBS15-16-800 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 which connects to a rod extending from the switch. NOJA Power plans to release a motorized, automated version of VISI-SWITCH, which will be controlled from the RC10 control and communication cubicle – a supervisory system used with the company’s OSM series Automatic Circuit Reclosers. The automated VISI-SWITCH will enable remote operation and sectionaliser functionality.
 
NOJA Power is constructing a new 5500-m² production facility at its Brisbane site to manufacture VISI-SWITCH. The unit is expected to be in full production by Q3 2016 with volume deliveries from Q4 2016.

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