NOJA Power Switchgear commends an amendment made by the IEC specifying testing of arc containment and venting to prevent catastrophic failure caused by phase-to-earth arcing in single-pole configured reclosers.
NOJA Power believes this international standard revision will encourage manufacturers to design products to fail in a controlled manner. Previous editions of the standard included IAC (internal arc classified) testing of phase-to-phase arcing in three-phase configured equipment, but omitted any requirement to classify phase-to-earth arcing in single-phase units.
According to electrical switchgear engineers NOJA Power, the amendment to the International Standard IEC 62271-200 (High-voltage switch gear and control gear – Part 200: AC metal-enclosed switchgear and control gear for rated voltages above 1 kV and up to and including 52 kV) recognises that phase-to-ground arcing in single-pole configured reclosers can be a cause of catastrophic failure and the units should be tested for such an eventuality.
Where the standard previously mandated testing solely for three-phase units, it now calls for additional single-phase testing obligating recloser manufacturers to ensure appropriate arc fault containment is incorporated into their products.
Arcing is mostly a result of lightning strikes causing a voltage spike that overwhelms the recloser’s surge arrester and exceeds the BIL rating of the insulation system. Multiple lightning strikes that degrade the insulation over time can also cause failure.
Modern reclosers using vacuum interrupters embedded inside cyclo-aliphatic epoxy resin poles are unlikely to have phase-to-phase arc faults but phase-to-earth faults can occur and cause failure of units that do not incorporate arc fault containment and venting, in a catastrophic and uncontrolled manner. However, reclosers designed for arc fault containment will fail in a controlled manner, eliminating danger to the general public, electricity workers and other equipment.
IEC’s amendment to the standard details how the containment of these products should be tested.
Section 6 and Annex AA of Edition 2.0 of the standard comprehensively describe the internal arc test requirements for metal-enclosed switchgear and control gear, intended to be qualified as internal arc classified (IAC).
Emphasising the importance of testing single-pole configured products, the standard notes that the ‘arc fault current’ is defined as ‘three-phase and – where applicable – the single phase-to-earth RMS value of the internal arc fault current for which the switchgear and control gear is designed to protect persons in the event of an internal arc’.
The CEO of NOJA Power, Neil O’Sullivan explains NOJA Power has always ensured that their solid dielectric auto recloser products have complied with the requirement for arc fault containment and venting as defined by IEC62271-200. In the event of failure, internal arcing is contained and any gases generated during arcing are safely vented.
O’Sullivan adds the amendments to the standard now imply that all solid dielectric equipment – even with single pole configurations – need to be arc fault contained and vented, making it an important step forward for this standard and the safety of pole-mounted switchgear.
NOJA Power's OSM range of medium-voltage (15, 27 and 38 kV) reclosers feature patented arc fault containment and venting achieved by manufacturing the tank from stainless steel and providing an arc vent in the pole side of the unit. In the event of arcing, the hot gases are directed towards the pole and upwards, away from maintenance staff or members of the public on the ground and minimising physical risk.
All NOJA Power reclosers have passed arc fault containment and venting testing conducted by Test & Certification Australia covering the five criteria specified in the international standard:
- Correctly secured doors and covers do not open
- No fragmentation of the enclosure for the duration of the test
- No projection of small parts, up to an individual mass of 60 g
- Arcing does not cause holes in the accessible sides of the enclosure up to a height of 2m
- Indicators do not ignite due to the effect of hot gases