Electrical switchgear engineers NOJA Power today advises that an amendment to the International Standard IEC 62271-200† 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. Previously the standard mandated testing solely for three-phase units; now the standard calls for additional single-phase testing obligating recloser manufacturers to ensure appropriate arc fault containment is incorporated into their products.
The most likely cause of arcing is lightning strikes causing a voltage spike that overwhelms the recloser’s surge arrester and exceeds that BIL rating of the insulation system. Failure could also be the result of multiple lightning strikes that degrade the insulation over time.
Although phase-to-phase arc faults in modern reclosers using vacuum interrupters embedded inside cyclo-aliphatic epoxy resin poles are unlikely, phase-to-earth faults can occur and units that incorporate no arc fault containment and venting can fail in a catastrophic and uncontrolled manner.
Reclosers that have been appropriately designed for arc fault containment will fail in a controlled manner, eliminating danger to the general public, electricity workers and other equipment. The 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 controlgear, intended to be qualified as internal arc classified (IAC).
In recognition of the importance of testing single-pole configured products, the standard goes on to note 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 controlgear is designed to protect persons in the event of an internal arc”.
Previous editions of the standard included IAC 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.
“NOJA Power commends the IEC for addressing the earlier omission in the latest version of IEC 62271-200,” said Neil O’Sullivan, CEO, NOJA Power.
“As a responsible and experienced switchgear producer, NOJA Power has always ensured that our solid dielectric auto recloser products have complied with the requirement for arc fault containment and venting as defined by IEC62271-200. If failure occurs, internal arcing is contained and any gases generated during arcing are safely vented,” explained O’Sullivan. “What the amendments to this standard now imply is that all solid dielectric equipment – even with single pole configurations – need to be arc fault contained and vented and this is 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 (see “About the NOJA Power OSM range”) 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 gasses are directed towards the pole and upwards, minimising the risk to maintenance staff or members of the public that may be on the ground below the recloser.
The products have passed arc fault containment and venting testing conducted by Test & Certification Australia and covering the five criterion 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 2 m, and indicators do not ignite due to the effect of hot gases.
† “High-voltage switchgear 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”