An internal arc fault is an unintentional discharge of electrical energy inside the switchgear. In the case of an internal arc, the arc energy rapidly heats the surrounding gas resulting in a pressure rise and mechanical stress on the enclosure.
If the switchgear enclosure is not strong enough, it can rupture. Before going to test to check the design integrity, it is important to calculate the pressure rise inside the switchgear compartments.
Using calculations, the pressure rise inside compartments during an internal arc can be reasonably predicted if the arc energy is known. This means that the arc energy should be taken from previous internal arc tests on similar switchgear designs.
In CFD software, pressure, temperature, and flow velocity are available at each point of the flow domain over time. The solver calculates the average gas pressure on surfaces or in the volume automatically. The post processing tools
allow animations (video) of the gas flow, providing a good visual to understand the phenomena.
Figure shows the pressure inside air-insulated switchgear compartment, 55 ms after initiation of internal arc calculate by CFD software.
