Protection of oil-filled transformer against explosion: Numerical simulations on a 200 MVA transformer

Oil filled transformer explosions and their prevention are a complex industrial issue. Experimental tests showed that when an electrical fault occurs in a transformer, it generates dynamic pressure waves that propagate in the oil. Reflections of these waves on the walls build up high static pressure which transformer tanks can not withstand. Besides, a numerical tool was developed to simulate the phenomena highlighted during the tests and mainly the pressure wave propagation. It is based on a compressible two-phase flow modelling where viscous flow, electromagnetic, thermal and gravity effects are taken into account. The equations are solved using a finite volume method allowing computing complex 3D transformer geometries. Simulations of the consequence of an electrical arc occurring in a 200 MVA transformer geometry show that the static pressure increase can be prevented by a quick oil evacuation triggered by the first dynamic pressure peak generated by the electrical arc.