Page 47 - Energize June 2021

TECHNICAL

Arc flash detection, reduction and

protection in switchgear

By Mike Rycroft, Now Media

Arc flash incidents are associated mainly with switchgear. Technology and safety procedures have
significantly reduced most other forms of electrical injuries, while incidents related to arc flash have
surfaced as one of the leading causes of injury and death to workers.

etection and reduction methods have advanced considerably, proximity to the switch. Personal protective equipment (PPE) can
but there is a large amount of older equipment in service limit the effect of AF on personnel. PPE covers a person’s head,
Dwhere arc flash incidents still occur. Where detection and face, body, hands and feet. The type and class of equipment will
reduction methods are limited, other methods can be applied to depend upon the AF risk level, which can be evaluated by taking the
reduce danger to operators and other personnel. type and size of installation into account.
The number of arc flash incidents that occur is difficult to The second stage is putting distance between the switch and
determine. Figures from the US indicate 30 000 electrical incidents the person working on it. The solution is the use of remote operated
per year of which 10% are estimated to be arc flash. UK figures switchgear or robots to remove, reinstall and activate switchgear.
1
suggest 1000 arc flash incidents per year. Another report suggests Many AF incidents occur when withdrawable components (e.g.,
five to ten incidents per day for the US (1800 to 3600 per year). circuit breakers, starter buckets, etc.) are inserted or withdrawn
Figures for South Africa are unavailable, but ongoing reports from equipment, when they are “racked” in or out. There is a wide
indicate that such incidents occur regularly. range of remote racking options now available for both low- and
medium-voltage equipment. The principle is much the same as with
Arc flash remote operation – the remote racking device allows the operator to
Arc faults (AF) occur between a conductor and earth, or significantly increase the working distance during these operations,
between phase conductors, and are due to the compromising of ideally to a point outside the range of a potential arc flash.
insulation or air isolation between energized components within Remote operation of circuit breakers or switches is an
an electrical circuit. AF can be caused by numerous factors, established technology that requires the breakers to be electrically
including dropped tools or pieces of wire, accidental contact by operated. Remote switching of devices may be done from remotely-
maintenance personnel, the build-up of corrosion or conductive mounted operating switches, pushbuttons, HMI screens, and even
dust on conductors, and the presence of pests, such as mice, over networking, through SCADA systems, network-connected
rats or snakes, that come into contact with energized conductors. relays, or other devices.
AF occurring in enclosed spaces, such as switchgear, can cause There are also portable devices that can be temporarily mounted
considerable damage. to control switches or other operating mechanisms. In all cases,
the ideal situation is for the remote operating point to be located
Arc flash characteristics beyond the range of a potential arc flash’s boundary.
A fully developed arc flash is characterised by temperatures
approaching 20 000°C, the expulsion of hot gases and vapourised
metal, and intense light (Figure 1). The energy released in an AF
is dependent on both the level of current flowing and the time for
which it is allowed to flow. The formation of an arc results in the
operation of the upstream breaker, but the short-circuit operation
time of most breakers is several cycles, time enough to allow the arc
to develop to its full extent.

Arc flash mitigation
Mitigation methods consist both of reducing the effects of AF and
the level of the energy released in the arc flash.
The first stage of arc flash mitigation is the provision of suitable
personal protective equipment for staff working with switchgear.
AF occurs during work on the switch, either jacking out, jacking in,
or making and breaking contacts, times when someone is in close Figure 1: Arc flash components (ABB)

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