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**TRANSFORMER PROTECTOR**

TRANSFORMER EXPLOSION PREVENTION Research and Experiments Dr. Guillaume Perigaud TPC 808 Russell Palmer Rd. Kingwood, TX 77339 Office: Fax:

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**TWO WAYS OF INVESTIGATION**

Numerical Simulations Experiments MTH model (Magneto Thermo Hydrodynamic ) 2002 Tests in EDF (Electricité de France) Upgrade to account for pressure wave propagation Compressible Effects (shock waves) Heat Transfers 2004 Tests at CEPEL (Centro de Pesquisas de Energia Eletrica) Arc Effects Two-Phase Flows Viscosity Gravity

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Physical Phenomena

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**TRANSFORMER EXPLOSION PREVENTION**

Dielectric Oil Insulation Rupture Electric Arc Oil Vaporisation Pressure Increase Locally Pressure Wave Propagation Pressure Wave/Structure Interaction Transformer Tank Explosion

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**TRANSFORMER EXPLOSION PREVENTION**

Dielectric Oil Insulation Rupture Electric Arc Oil Vaporisation Pressure Increase Locally Pressure Wave Propagation Pressure Wave/Structure Interaction Tank Depressurisation TRANSFORMER PROTECTOR Transformer Tank Saved

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**TRANSFORMER EXPLOSION PREVENTION**

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 PROTECTOR OPERATION Tank Depressurisation Energy Evacuation During the Whole Arcing (more than 100ms) Transformer Tank Saved

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**Gas bubbles appear on the arc path (1 to 2.3 m3 i.e. 35 to 80 ft3). **

GAS GENERATION 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 m3 i.e. 35 to 80 ft3). Gas gets under pressure (from 100 bar/sec to 5,000 bar/sec i.e ,500 Psi/sec to 72,500 Psi/sec) The pressure rise up to 14 bar (200 Psi). Movie : Test Number: 3 Date: 06/04/2002 Test Reference: 2002 Arc Current: 2500 A Arc Duration: 79 ms Camera Speed: 3000 frames/second

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**PRESSURE DYNAMIC BEHAVIOR DURING A LOW IMPEDANCE FAULT**

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.

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TP Operation

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** TP OPERATION 1/ Pressure rises**

2/ Explosion of the disk, depressurisation, evacuation of the oil-gases mixture 3/ Opening of the air isolation shutter 4/ Nitrogen injection N2 5/ Explosive gases production is stopped

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**TP OPERATION Test Movie 20 MVA TRANSFORMER TEST Test Number: 30 Date:**

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

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**PRESSURE VARIATION DURING THE TP OPERATION**

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 Gradient 3900 bar/sec (56,550 Psi/sec) Pressure peak 7.5 bar (109 Psi)

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**DEPRESSURISATION KEY OF SUCCESS**

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.

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**TRANSFORMER TANK RESPONSE TO THE PRESSURE RISE**

Dynamic Behavior Static Behavior Very transient phenomenon, from 25 bar/s, (360 psi) to 5000 bar/sec (72,500 psi/sec) Very slow phenomenon, below 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) Local Mechanical Stresses Uniform and Isotropic 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

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**TRANSFORMER DIMENSIONS ARE MORE IMPORTANT THAN POWER (MVA)**

CEPEL tests T3 transformer = 8.5m (28 ft) Since the pressure wave propagate at a finite speed, the bigger the transformer, the longer the propagation time to reach the TP.

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**Shock Wave Simulation on a Very Large Transformer**

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750 MVA SIMULATION 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.

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**750 MVA SIMULATION Magnetic Core Arc Location S6 S7 S8 3.8 m**

(12.66 ft) Ø 0.3 m (12 in) 16 17 18 S2 S3 3 4 5 6 7 8 9 10 11 S1 TP 9.14 m (30 ft) 0.5m (1.66ft) 0.5m (1.66ft) Magnetic Core 5.2 m (17.33 ft) 4.8 m (15.75 ft) Ø 0.05 m (1.97 in) 12 4.2 m (14 ft) 2 S4 S5 Arc Location 1 15 14 13 1 m (3.33 ft) 9.9 m (33 ft)

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**750 MVA SIMULATION: PRESSURE MAPS**

T= 0 ms T= 18 ms T= 42 ms T= 60 ms T= 102 ms

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**750 MVA SIMULATION: VELOCITY MAPS**

T= 0 ms T= 18 ms T= 42 ms T= 60 ms T= 102 ms

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750 MVA SIMULATION 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.

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Conclusion

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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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**Thanks for your kind attention ….**

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