Arc Flash in Wind Turbines
Arc flash accidents are not nearly as rare as is often imagined, and the hazards they create are severe. In wind turbines, these hazards are further magnified. Here, Angus Long of SKANWEAR explains why and examines ways in which the perils of arc flash accidents can be minimised.
Almost everyone who works with electricity has heard of arc flash accidents and many know that such accidents can be extremely dangerous. Ask them, however, how common these accidents are and most will say that they are exceptionally rare. Unfortunately, that’s not a particularly accurate assessment. In fact, EU statistics show that between eight and ten arc flash accidents occur in the UK every week.
Clearly, arc flash is not a phenomenon that anyone can afford to ignore, least of all as we shall see, those who work on wind turbines. But what exactly is an arc flash accident and how do such accidents occur?
In simple terms, an arc flash accident happens when a large electrical current passes through ionised air and gasses. These accidents can be triggered in many ways, but examples are when a conductive tool is dropped across live busbars while maintenance is being performed, or when a circuit breaker fails during a switching operation. Statistics show that arc flash accidents most commonly occur in LV systems.
Arc flash accidents produce dramatic results. Almost instantaneously, the temperature near the arc increases by around 20,000ºC. This vaporises copper conductors and, since the volume of the vapour produced is around 67,000 times that of the metal, a violent explosion results. Secondary effects include the expulsion of globules of molten copper, an intensely bright flash of light and the generation of pressure waves.
It’s easy to see that when such an accident occurs, there is a very high risk that any person in the vicinity will be severely injured or even killed. Further, the equipment in which the fault occurs will usually be damaged beyond repair.
Now consider the situation in a wind turbine. The immediate effects of the arc flash accident are unchanged, but dealing with the consequences is much more difficult. For example, getting medical treatment to a badly injured person is no trivial matter if they are working in a nacelle tens of metres above ground or sea level. And rescuing the injured person is likely to prove equally challenging, especially as many wind farms are in remote locations or even offshore.
The consequences of equipment damage are also exacerbated. While replacing a damaged switchboard in building is no easy task, replacing switchgear in a turbine nacelle is even more difficult and even more costly. And it’s also necessary to think about the loss in revenue resulting from the wind turbine’s inability to generate electricity until repairs have been carried out – which could be weeks or even months.
With all of this in mind, it’s unsurprising that arc flash accidents are attracting a lot of attention not only from electrical engineers, but also from health and safety professionals. But what can realistically be done to minimise the occurrence and impact of these events?
The first step is to try to eliminate the conditions under which arc flash accidents can occur, ideally by not working on live equipment. Indeed, Regulation 14 of the Electricity at Work Regulations makes it clear that live working should never be accepted as the norm, and that it must only be sanctioned under specific conditions, one of which is that suitable precautions must be taken to prevent injury.
It’s worth bearing in mind, however, that arc flash accidents are not limited to situations where live working is being carried out intentionally. An arguably greater risk relates to those situations where an “isolated” system is accidentally made live while it is being worked on.
In truth, there is no 100% certain way of completely eliminating arc flash accidents, although the risk can be greatly reduced by specifying switchgear that features insulated arc-free busbar assemblies. Unfortunately, such switchgear is larger than conventional equipment and is, therefore, unlikely to find favour in wind turbine applications.
One way of minimising risks is to provide those working on electrical equipment with suitable personal protective equipment (PPE). Indeed, the Protective Equipment at Work Regulations 1992 make it mandatory for employers to provide PPE if a risk assessment indicates that it is needed. The same regulations make it very clear, however, the use of PPE is a last resort because it does not control the problem at source, and it protects only the wearer which is fundamentally your greatest asset!
ARC FLASH CLOTHING & PROTECTION is your last line of defence but it’s mandatory that PPE is issued. There is no excuse ever for Arc Flash burns as they avoidable. Speak to SKANWEAR to learn not only what PPE protection you need but also what other protective measures you can implement to avoid the potentially fatal effects of an arc flash.
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