Electrical switchgear engineers NOJA Power today announces the release of a video graphically demonstrating the unique arc fault containment and venting feature of the company’s OSM series solid dielectric insulated Automatic Circuit Reclosers (ACR).
The video can be viewed on NOJA Power’s website ( http://www.nojapower.com.au/typetest/recloser-arc-fault-containment-solid-dielectric.html ) and demonstrates an ACR subjected to a 12.5-kA, 1-second arc fault during type-testing. The video shows that the explosion caused by the fault is contained within the ACR’s stainless steel tank while the flames and hot gases from the explosion are safely vented.
Later, the video switches to the area immediately under the pole-mounted ACR. For the test, this area is covered in feather fabric to mimic human skin and indicate if any debris, hot gases or flames would endanger people on the ground. After the explosion the feather fabric is undamaged.
A previous generation of ACRs used Sulphur Hexafluoride (SF6) gas for insulation. Because the gas was contained within a pressure vessel, arc fault explosions were contained. However, SF6 has now fallen out of favour because the gas has been shown to have a potent global warming potential of 23,900 times that of CO2. Modern devices––including every NOJA Power ACR ever made––employ environmentally-neutral solid dielectric insulation. Solid dielectric insulated ACRs do not require the SF6 pressure vessels used in older products but the absence of the vessel eliminates arc fault containment.
Yet contemporary working practices include more live line installations and maintenance activities demanding that utility staff approach energised switchgear more regularly. Uncontained arc fault explosions in solid dielectric ACRs are a major safety hazard for these workers. Unlike all competitive products, NOJA Power’s OSM series ACR addresses this hazard by employing a stainless steel containment tank that resists arc fault explosions and harmlessly vents hot gases.
The tank’s pole mounting forms a chimney that ensures the arc and hot gases are vented upwards. The arc vent’s position at the back of the ACR, closest to the pole, allows maintenance crews to approach the unit from the non-pole side safe in the knowledge that any arc fault failure will be directed away and upwards from their line of approach.
The arc fault containment and venting feature has been designed in accordance with IEC62271-200* Clause 6.106 and Annex A. NOJA Power’s OSM series ACR has passed the arc fault containment type-test and complies with the following criteria:
- Correctly secured doors and covers do not open;
- No fragmentation of the enclosure occurs within the time specified for the test;
- Projections of small parts, up to an individual mass of 60 g;
- Arcing does not cause holes in the accessible sides up to a height of 2 m;
- Indicators do not ignite due to the effect of hot gases;
- The enclosure remains connected to its grounding point.
“Safety and environmental responsibility are paramount for NOJA Power,” says Neil O’Sullivan, Managing Director of the company. “All of our OSM series ACRs are built using non-polluting solid dielectric insulators, but we wanted to take the design one step further and ensure utility staff were protected in the event of an ACR suffering an arc fault failure in their vicinity. The 12.5-kA, 1-second arc fault test dissipates a tremendous amount of energy and the fact that our tank has been proven to safely contain and vent this energy is a testament to its design and structural integrity.
“NOJA Power’s products are the only solid dielectric insulated ACRs with type-tested arc fault containment commercially available anywhere in the world.”
Units from NOJA Power's OSM series of medium-voltage (15, 27 and 38 kV) ACRs (see “About the NOJA Power OSM range” below) have been installed by utilities in over 80 countries around the world. The ACRs have been subjected to full type testing by independent test laboratories such as KEMA in the Netherlands to the latest standards - underscoring the superior safety and performance of NOJA Power’s protection solutions.
* “IEC 62271-200: 2011 High-voltage switchgear and controlgear - Part 200: AC metal-enclosed switchgear and controlgear for rated voltages above 1 kV and up to and including 52 kV”.
References: 1. "Direct Global Warming Potentials", Intergovernmental Panel on Climate Change. 2007.