I found a copy of a CIGRE document entitled "Tools for the Simulation of Effects of the Internal Arc in Transmission and Distribution Switchgear". What I found most fascinating about it is that it is clearly demonstrating that there have been a lot of advances in an understanding of arc blast. For instance on page 38, it gives the following equation for calculating the pressure before some kind of rupture/release event:
p(t)=p_init+(Kappa1)Qt/V where: p(t) = pressure as a function of time p_init = initial pressure Kappa = heat capacity ratio, 1.403 for air and 1.0936 for SF6 V = volume (cubic meters) t = time (seconds) Q = energy input, given as kW where k is a constant generally around 0.4 to 0.65 which represents the amount of arcing power that gets converted into heat, and W is the power in the arc. The models generally use 0.5(V_arc)(I_arc). Formula for V_arc is given as: V_arc/d = 30*V+0.5*I*V where d is the gap distance in centimeters, V is the phasetophsae voltage, and I is the short circuit current in kA. Valid for V_arc/d < 40 V/cm.
What I'm finding fascinating is that it's linear and easily predicted. What is a little more complicated and says so further in the same document is that because the rise time of the pressure is very short, plastic deformation doesn't always happen so failure modes of the enclosures can get tricky to predict and they recommend finite element.
