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Stage One - Arc Flash Studies

Arc Flash is a rapid release of energy due to an arcing fault between a phase bus bar and another phase bus bar, neutral or a ground. During an arc fault the plasma channel created in the air acts as the conductor.

Arc Flash is most commonly caused by human error (tools left in switchgear compartments, drilling through the cables etc.) but can be also related to switchgear failure (CB failure during switching, isolation fault), environmental conditions (dust build-up or moisture/humidity inside the switchgear), loose electrical connections or even external influences (weather, animals etc.).

Arc Flash Effects include:
- Heat
- Pressure
- Sound waves
- Projectiles
- Molten metal
- Toxic gases

Arc flash studies determine the achievable energy during faults at various points in the system, and based on the energy levels and the distance from the energy source, the minimum required PPE levels are determined. As the energy is dependent on the fault current and the fault duration, a protection assessment is typically carried out to determine any possible reduction in achieved energy levels, and therefore, smaller PPE requirements.

A site survey might be required to gather data required for the arc flash studies, which can include information like system generation, demand, switchgear, cabling, protection relay type and settings, and available clearances between the switchgear and walls/panels etc. During the site survey we would typically gather all other relevant information about operational procedures, PPE requirements that are already in place, the switchgear information, plant generation and loading modes. All the information gathered will be used to create a "Digital Twin" of the power system to carry out the arc flash studies. This model can be used for a variety of other study types detailed in Power System Analysis .

Impedance tolerance models play an important part in assessing the worst case scenario for Arc Flash energies. A classic example is the overcurrent protection with instantaneous setting, where the fault levels exceed the instantaneous setting operation by a small margin. If the fault level drops as a result of higher impedance on the fault path, the protection relay could then take longer to operate (i.e. low setting with IDMT characteristic) and the calculated arc flash levels would increase considerably, as shown on the picture below.