Internal Arc Simulation in MV/LV Substations Charles BESNARD 8 11 June 2009
The Internal Arc Fault The fault A highly energetic and destructive arc (10, 20, 40 MJ!) The effects and the human risks Overpressures can cause parts ejection or wall rupture Hot gases flows can burn on their way On The equipment > 62271-200 std > Type test for a given equipment > Simulation The surrounding (Substation / Electrical room) > (62271-202 std) > not a test for each customized surrounding! > Simulation can help! 2
The internal arc simulation tool A frame: Fluid Dynamics software A Physical description method of internal arc fault: Equivalent energy injection Equivalent mass injection (plastic vaporization) Radiation, air properties at high temperatures, To get pressure and gas channeling in every self-designed geometry including: Equipment But also customized surrounding 3
Simulation in the equipment Inputs Simplified geometry A ring main unit Electrical parameters 16 ka, 3-phases fault Fault location Switch compartment Switch compartment Cable compartment Arc location Buffer Volume Computation I (A) 40000 30000 20000 10000-20000 -30000-40000 -50000 Short-circuit currents 0 0-10000 0,02 0,04 0,06 0,08 0,1 Time (s) I1 I2 I3 Power (W) 2,5E+07 2,0E+07 1,5E+07 1,0E+07 5,0E+06 0,0E+00 Instant Power 0 0,05 0,1 0,15 0,2 Time (s) 4
Simulation in the equipment Pressure cartography and gas channeling Shock wave (2ms) Pressure rise and decompression (50ms) Outputs Pressure curves are validated through a type-test 5
Simulation in a variable surrounding Vent area Average configuration Room volume 300x300 1000x1000 600x600 16 ka 20 m 3 50 m 3 15 m 3 Decompression Interface 200x200 150x150 300x300 6
Simulation in a variable surrounding The point of interest is the average pressure in the substation Note that some wall regions are overstressed, what has to be analyzed with pressure maps video 7
Conclusion People become more and more concerned about knowing overpressures in their substations or electrical rooms, consecutively to an arc fault Surroundings of electrical equipments are widely diversified It is a question of people safety and building protection Numerical simulation has a strong role to play in this field, because a type test can not be performed on each unique customer s facility The simulations take advantage of a generic tool describing the fault, inside and outside the equipment A customized design can be simulated to match the reality as close as possible It is a prospective for the evolution of 62271-200/202 standards to take into account the overpressure in the surroundings 8
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Appendices Max pressure? Average pressure? What has to be considered Usually, the average pressure in the room, exerted on the entire wall gives the highest equivalent load The max pressure is obtained locally (in front of exhaust) and does not extert on the entire wall It can be taken into account with pressure maps 10
Appendices The parameters of the room can hardly have an influence on the pressure inside the device However, the parameters at the interface switchgear / room are very important The exhaust area (varying 170%) between buffer volume and room can change the pressure inside the buffer volume (varying 70%) 11
Appendices The internal arc fault implies thermal exchanges as pressure rises The ones depend on the others That is why a CFD description is appropriated, to integrate all the effects 12
Appendices Other examples A modular switchgear, with upper exhaust 13