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Sergi Holding, Research Department, IEEE Task Force, 2006 March 21 rst TRANSFORMER PROTECTOR Dr. Guillaume Perigaud TPC 808 Russell Palmer Rd. Kingwood, TX Office: Fax: TRANSFORMER EXPLOSION PREVENTION Research and Experiments

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Sergi Holding, Research Department, IEEE Task Force, 2006 March 21 rst Numerical Simulations MTH model (Magneto Thermo Hydrodynamic ) Upgrade to account for pressure wave propagation Compressible Effects (shock waves) Viscosity Gravity Heat Transfers Two-Phase Flows Arc Effects TWO WAYS OF INVESTIGATION Experiments 2002 Tests in EDF (Electricité de France) 2004 Tests at CEPEL (Centro de Pesquisas de Energia Eletrica)

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Sergi Holding, Research Department, IEEE Task Force, 2006 March 21 rst Physical Phenomena

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Sergi Holding, Research Department, IEEE Task Force, 2006 March 21 rst TRANSFORMER EXPLOSION PREVENTION Pressure Wave/Structure Interaction Transformer Tank Explosion Dielectric Oil Insulation Rupture Electric Arc Oil Vaporisation Pressure Wave Propagation Pressure Increase Locally

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Sergi Holding, Research Department, IEEE Task Force, 2006 March 21 rst Transformer Tank Saved Tank Depressurisation TRANSFORMER PROTECTOR Pressure Wave/Structure Interaction Dielectric Oil Insulation Rupture Electric Arc Oil Vaporisation Pressure Wave Propagation Pressure Increase Locally TRANSFORMER EXPLOSION PREVENTION

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Sergi Holding, Research Department, IEEE Task Force, 2006 March 21 rst Energy Evacuation During the Whole Arcing (more than 100ms) Transformer Tank Saved Tank Depressurisation TRANSFORMER PROTECTOR OPERATION Pressure Wave/Structure Interaction Depressurisation Set Designed as Transformer Tank Structure Weakest Point in term of Rupture Inertia to Dynamic Pressure Very Fast Depressurisation Set Opening (less than 2 ms) TRANSFORMER EXPLOSION PREVENTION

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Sergi Holding, Research Department, IEEE Task Force, 2006 March 21 rst Test Number:3Date:06/04/2002 Test Reference:2002 Arc Current:2500 A Arc Duration:79 ms Camera Speed:3000 frames/second Very violent physical phenomena (tank acceleration up to 400g where g=9.81 m/sec² i.e. 30 ft/sec²). Gas bubbles appear on the arc path (1 to 2.3 m 3 i.e. 35 to 80 ft 3 ). Gas gets under pressure (from 100 bar/sec to 5,000 bar/sec i.e. 14,500 Psi/sec to 72,500 Psi/sec) The pressure rise up to 14 bar (200 Psi). Movie : GAS GENERATION

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Sergi Holding, Research Department, IEEE Task Force, 2006 March 21 rst The pressure variation is a very transient phenomena that is non-spatially uniform. Pressure waves are acoustic waves, which propagate throughout the tank at finite speed, the speed of sound in the oil (1,200 m/sec i.e ft/s). The tank structure has a large influence on the local pressure. PRESSURE DYNAMIC BEHAVIOR DURING A LOW IMPEDANCE FAULT

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Sergi Holding, Research Department, IEEE Task Force, 2006 March 21 rst TP Operation

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Sergi Holding, Research Department, IEEE Task Force, 2006 March 21 rst 1/ Pressure rises 2/ Explosion of the disk, depressurisation, evacuation of the oil-gases mixture 4/ Nitrogen injection N2N2 3/ Opening of the air isolation shutter 5/ Explosive gases production is stopped TP OPERATION

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Sergi Holding, Research Department, IEEE Task Force, 2006 March 21 rst 20 MVA TRANSFORMER TEST Test Number:30Date:12/07/2004 Test Reference:30_T1C_140_83_VAC Arc Current:14000 A Arc Duration:83 ms Arc Location:Opposite the TP close to the bottom TP Operation:Under Vacuum Camera Speed:25 frames/second Test Movie TP OPERATION

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Sergi Holding, Research Department, IEEE Task Force, 2006 March 21 rst Test Number: 32 Arc Current: A Arc Duration: 83 ms Arc Location: At the tank cover in the TP vicinity (A) Under atmospheric Pressure Pressure peak 7.5 bar (109 Psi) PRESSURE VARIATION DURING THE TP OPERATION Pressure Gradient 3900 bar/sec (56,550 Psi/sec)

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Sergi Holding, Research Department, IEEE Task Force, 2006 March 21 rst To create an opening for the pressure to be evacuated before the transformer tank sees the increased static pressure : The tank rupture inertia > 60 milliseconds for pressure peaks up to 14 BAR (200 PSI) and pressure gradients from 100 bar/sec (14,500Psi/sec) to 5,000 bar/sec (75,000 Psi/sec); TP inertia to open < 2 milliseconds. DEPRESSURISATION KEY OF SUCCESS

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Sergi Holding, Research Department, IEEE Task Force, 2006 March 21 rst Dynamic BehaviorStatic Behavior Very transient phenomenon, from 25 bar/s, (360 psi) to 5000 bar/sec (72,500 psi/sec) Very slow phenomenon, below 25 bar/sec (360 psi/sec) Pressure spatially non-uniform Pressure spatially uniform Very High Local Overpressure for less than 60 milliseconds (>+14 bar, +200 Psi) Low Global Overpressure for more than 200 milliseconds (<+1.2 bar, 17 Psi) Uniform and Isotropic Mechanical stresses Local Mechanical Stresses Tank withstands the local high overpressure because of walls elasticity Tank does not withstand the global low overpressure in spite of the walls elasticity TRANSFORMER TANK RESPONSE TO THE PRESSURE RISE

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Sergi Holding, Research Department, IEEE Task Force, 2006 March 21 rst Since the pressure wave propagate at a finite speed, the bigger the transformer, the longer the propagation time to reach the TP. CEPEL tests T3 transformer = 8.5m (28 ft) TRANSFORMER DIMENSIONS ARE MORE IMPORTANT THAN POWER (MVA)

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Sergi Holding, Research Department, IEEE Task Force, 2006 March 21 rst Shock Wave Simulation on a Very Large Transformer

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Sergi Holding, Research Department, IEEE Task Force, 2006 March 21 rst The transformer dimensions are the parameters that matter the most; The maximum distance between an arc and the TP is about 15 m (49 ft); The extrapolation ratio between the CEPEL 20 MVA and the 750 MVA transformers is only 2, not 35; The arc current is chosen equal to 70 kA during 70 ms. 750 MVA SIMULATION

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Sergi Holding, Research Department, IEEE Task Force, 2006 March 21 rst 9.9 m (33 ft) 1 m (3.33 ft) TP m (15.75 ft) Ø 0.3 m (12 in) Ø 0.05 m (1.97 in) S6S6 S7S7 S8S8 S3S3 S2S2 S5S5 S4S4 S1S1 5.2 m (17.33 ft) 4.2 m (14 ft) 9.14 m (30 ft) 0.5m (1.66ft) 3.8 m (12.66 ft) 750 MVA SIMULATION Magnetic Core Arc Location

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Sergi Holding, Research Department, IEEE Task Force, 2006 March 21 rst T= 0 ms T= 42 ms T= 18 ms T= 60 ms T= 102 ms 750 MVA SIMULATION: PRESSURE MAPS

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Sergi Holding, Research Department, IEEE Task Force, 2006 March 21 rst T= 0 ms T= 42 ms T= 18 ms T= 60 ms T= 102 ms 750 MVA SIMULATION: VELOCITY MAPS

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Sergi Holding, Research Department, IEEE Task Force, 2006 March 21 rst The study of the pressure and velocity maps explains the depressurisation process; The TP activates in 18 milliseconds; The transformer is depressurised in 60 milliseconds; Pressure peaks are located in the transformer body, but in the bushings as well because of geometry influence on the pressure. 750 MVA SIMULATION

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Sergi Holding, Research Department, IEEE Task Force, 2006 March 21 rst Conclusion

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Sergi Holding, Research Department, IEEE Task Force, 2006 March 21 rst CONCLUSION The experimental tests proved that the previous transformer explosion prevention strategy is efficient: the TP prevented the transformer explosion each time during the experiments. The simulations take into account the compressible effects and describe very accurately the pressure wave propagation. The pressure waves propagate at finite speed so that the transformer dimensions are the only parameter that matters in an explosion prevention strategy. The numerical simulations showed that only one Depressurisation Set is sufficient to depressurise a 750 MVA transformer in milliseconds. Despite this result, 2 Depressurisation Sets equip the transformers from 500 MVA.

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Sergi Holding, Research Department, IEEE Task Force, 2006 March 21 rst Thanks for your kind attention ….

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