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Reducing arc flash hazards

Joe Bush, Editor

16/01/2012

Tags: News

Eaton has developed a range of technologies and philosophies to counter the dangerous threat of arc flash in offshore applications. Larry Stahl, global director, Oil & Gas - Electrical Sector, Eaton Corporation, explains

Safety is of course of upmost importance in the offshore oil and gas sector. However, it is not simply about protecting the environment - effective protection of personnel and equipment is also crucial. In electrical installations specifically, one of the most serious hazards is arc flash.

Larry Stahl, global director, Oil & Gas - Electrical Sector, Eaton Corporation, said, “Arc flash safety is historically something that has been ignored. However several dynamics such as larger systems, less impedance and ageing equipment has led to arc flash becoming a real issue.”

Arc flashes occur when a large electrical current passes through ionised air. Fortunately they are rare, however, when they do occur the consequences are invariably serious, disruptive and costly. In an arc flash accident, the temperature in the vicinity of the arc rises almost instantly to around 20,000°C. Copper conductors are vaporised, leading to an explosion that expels molten globules of copper.

This all invariably leads to severely damaged, or in some cases destroyed equipment, and anyone in the vicinity of the incident is at high risk of injury or even death. The direct costs are high but in the offshore sector in particular, the indirect costs of lost production can be enormous.

There are numerous ways in which an arc flash can occur. For example, it can be triggered when a circuit breaker fails during a switching operation, or when insulation suffers a catastrophic breakdown. In reality, the risk of arc flash accidents can never be eliminated entirely.

Reducing the risk

Over many years Eaton has made significant investments into finding ways in which this risk can be greatly reduced. As a result, the company now offers more than 40 products and solutions for arc flash prevention and control.

Eaton has adopted the practice of designing its switchgear from the outset to minimise arc flash hazards. This has led it to adopt moulded insulation for its MV products, which allows excellent control to be achieved over electric fields, thereby reducing the susceptibility of the insulation to breakdown. The company also makes use of vacuum switching elements in its MV switchgear. As these are not susceptible to the effects of contaminants and moisture, and because they require no maintenance, they virtually eliminate the risk of failures during switching operations.

A further important benefit of using moulded insulation and vacuum interrupters is that the switchgear has minimal environmental impact during its life and also at the time of its eventual disposal. This contrasts strongly with switchgear that uses SF6 as an insulating agent, as this gas is a well known agent of environmental damage.

Arcon

For low voltage systems, Eaton has developed its Arcon system which adopts an active approach to minimising the effects of arc flash accidents. Arcon places a bolted short circuit across the supply within milliseconds of an arc being detected. The energy that would otherwise feed the arc is therefore diverted to the short circuit so that the arc never has a chance to develop. The upstream circuit breaker will subsequently interrupt the supply in about 50ms.

Arcon uses a device that puts the bolted short circuit in place within around 2ms of being triggered, and a detection system that is capable of reacting to an arc in its very earliest stages. The detection system uses a photodetector comprising a flexible fibre optic cable that is routed through all the areas of the switchboard where an arc fault might occur. The cable detects light over its entire length and when it sees the characteristic flash of an arc, it sends a signal to a logic module that also monitors current. If the photodetector signal is accompanied by a rapid increase in current, the module triggers the short circuiting device, and the arc is suppressed.

This arrangement minimises the risk of arc flash injuries and damage to the switchboard, allowing it to be returned to service rapidly and cost effectively.

Additional protection

However, whatever the technology the risk of arc flash accidents cannot be eliminated entirely. Because of this, Eaton also offers an assessment service for electrical installations, designed to ensure that all major risks, including arc flash, are properly assessed and that appropriate protective measures are put in place.

Stahl continued, “Arc flashes obviously have financial and personal liability consequences, but Eaton can conduct comprehensive studies on live equipment and can retro-fit solutions during a scheduled shutdown.

“Part of the solution to reducing the risk of arc flash is also to educate employees by making them fully aware of the dangers, make sure equipment is properly labelled, and to ensure appropriate personal protective equipment (PPE) is worn - as in most cases work has to be undertaken on live equipment.

“In the future we are also aiming to introduce to Europe Eaton’s IEE ESW (Electrical Safety Workshop) which has been running in the US for over ten years.”

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