Dealing with arc blast pressure through calculations and preventive measures

When the insulation between two energized phase conductors on powered electrical equipment malfunctions, current flows through the air instead of via a conductor, releasing thermal energy into its environment. The explosive energy burst during this ‘arc flash’ is known as an ‘arc blast’. Arc blast strength largely depends on how powerful the arc flash is, and the level of pressure it creates.

Our client wanted to know whether specified walls and installed circuit breaker could withstand different blast scenarios,” explains Arnau Sans, Lead Engineer at HyTEPS. “Another client with a huge vat located close to a staircase with medium voltage supply (in an open electrical cabinet with electrodes located on top) wanted to determine what might happen in case of an arc on the vat electrodes. The results show customers what energy levels they can expect and the pressure that will grow inside a building, including forces at different distances and locations. Based on incident energy, initial arc blast pressure, arc blast pressure increase, temperature and heat transfer and a proprietary calculation method, HyTEPS offered recommendations in both cases. These included lowering the relay short-circuit time setting, installing a pressure and toxic vapor release valve along with a wall that can handle pressure, and integrating a pressure release valve to the exterior.

Often, the customer or company responsible for designing and building the installation hasn’t considered the fact that arc blast pressure can be so destructive, or even that an arc flash might take place at their locations. Therefore, safety measures and further calculations must be performed once everything is well installed. It is better to perform simulations during the design stage as otherwise the solution becomes then more expensive.

This was an interesting project, as it required a different approach to ‘regular’ arc flash measurements. For a ‘regular’ arc flash measurement you need the details of the cabinet and installation in question. Based on the resulting energy value, you can define PPE. For an arc blast calculation, however you also need building data, such as measurements, layout, and volume. Placement of structural elements and the physical distribution of electrical components in real-life situations is also surprising in some cases.

I definitely have better insight into arc blast pressure studies and results and can better provide customer recommendations based on extensive research focused on how to interpret the pressure results and how to solve the related issues. The first steps are to develop deep knowledge on arc flash standard calculations, understand the simulation outcome, and get a good sense of what the results mean. I learnt quite a bit about arc blast pressure events – how they are created, which damage they may cause – as well as about the research done on this complete topic and understanding the formulas and methodologies.


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