There are a variety of factors to consider when it comes to battery maintenance, but understanding arc flash is an important one. While arc flash is fairly understood in AC systems due to testing, in DC systems (which includes storage systems) much of the research is based on theory that takes into account worst-case scenarios. Luckily the National Fire Protection Association (NFPA) and the Institute of Electrical and Electronics Engineers (IEEE) establish standards to ensure employee safety, as well as safety for companies like us who are charged with installing and maintaining battery systems. But before we get too far ahead of ourselves, let's discuss exactly what arc flash is.
What Is Arc Flash?
Per this excellent white paper, the IEEE describes arc flash as “a hazardous event usually caused by a metallic tool, test probe, under-rated test instrument or loose equipment part contacting energized bare parts and creating a short circuit or ground fault. It is an explosion with a loud noise, bright light, smoke emitted, and parts thrown. A person standing nearby may be injured or killed. The most common injury is severe burns caused by the intense heat which can ignite clothing.” While it is important to gauge the risk of DC voltage systems to determine the correct Personnel Protective Equipment (PPE), the nature of DC arc flash hazards make that a tricky proposition.
What Kinds of Hazards Are There?
Stationary batteries carry a variety of hazards. While the chemical, shock, and thermal hazards are more or less understood, DC arc flash hazards represent more of an unknown. There are a variety of equations to determine the minimum and maximum arc flash, and both scenarios require trial and error—and, of course, the appropriate PPE. Once again, per Cantor's white paper, any current models "do not take into account the dynamic energy of an electro-chemical device." However, there are some design practices that can minimize the hazards.
Hazard Avoidance, By Design
There are a few practices that system designers can employ to allay or remove arc flash hazards in stationary batteries, such as:
- Leaving large gaps between battery points when the differential voltage is higher than 100 volts
- Negative and positive battery terminals should never live in close proximity (and this is critical for DC systems with higher voltages)
- To reduce the potential for shorts, main battery terminals should be spaced widely apart
- Those same terminals—if they're over 100 volts—should be covered with nonconductive material
- Batteries should have the ability to be segmented to reduce arc flash potential, especially in cabinetized systems
As Always, Leave Maintenance to the Professionals
In the future, testing will hopefully provide additional data regarding what can cause a DC flash event. More places are having studies done, simply for insurance needs. Still, you need a maintenance partner that can install a safe system, maintain it, and provide safety guidance to your employees. Arc flash is another example of what can go wrong with your system if it's not accounted for from the beginning, and if a watchful eye is not kept over it going forward.