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Study SF 6 Thermal Plasma generated during/after power interruption

Final Project for Introduction to Plasma Processing Instructor: Prof. Kasra Etemadi STUDENT: Hosny, Ahmed A. Study SF 6 Thermal Plasma generated during/after power interruption. EE403/503, Fall 2005. Outline. Introduction Plasma characteristics Advantages and Disadvantages of SF 6

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Study SF 6 Thermal Plasma generated during/after power interruption

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  1. Final Project for Introduction to Plasma Processing Instructor: Prof. Kasra Etemadi STUDENT: Hosny, Ahmed A. Study SF6 Thermal Plasma generated during/after power interruption EE403/503, Fall 2005

  2. Outline • Introduction • Plasma characteristics • Advantages and Disadvantages of SF6 • Residual SF6 plasma species • Gas Insulated Switchgear (GIS) • Conclusion • Future work • References Hosny, Ahmed

  3. Electric Sub-circuit A V, I Circuit Breaker (CB) ON/Off V, I Electric Sub-circuit B What is Circuit Breaker (CB)? • CB is one of the most essential safety mechanisms in electric networks. • Interrupt short circuit currents (~ 60kA, low pf ~ 0.1). • Fault clearance time is very important for power system stability and avoid equipment damage for itself and the rest of the network. • CB can be characterized by, short circuit current, Rated voltage, … Figure 1: A schematic of Circuit Breaker Conditions Hosny, Ahmed

  4. Power Source materials Plasma + + + + + + Coupling Breakdown + + + Impulse Voltage, Transient Recovery Voltage (TRV) Manmade Plasmas Gas ( SF6) Plasma Elements… Extinguish Figure 2: A plot shows plasma elements. Hosny, Ahmed

  5. 105 Thermonuclear Plasmas Debye Length 1 cm 104 Electron Beam 1 m [m] 103 Solar Corona Average Electron Energy, [eV] 1 nm 1 m 102 P = 100 MHz P = 10 GHz P = 10 KHz P = 1 MHz P = 1 THz P = 100 Hz 1 mm Plasma Frequency Glow Discharge 1 Å 101 Gaseous Nebulae Interstellar Gas Arc Discharge 100 MHD Generator Ionosphere Solid 10-1 100 102 104 108 1010 1012 1014 1016 1018 1020 1022 1024 106 Electron Number density, [cm-3] Plasma Parameters… Hosny, Ahmed

  6. Plasma … Power Source Transient Recovery Voltage (TRV) • TRV is the voltage that builds up across a circuit breaker after the interruption of a fault current. • It consists of oscillations of lumped elements and of traveling waves. • It stresses the circuit breaker contacts and depends on the type and location of the fault in addition to the CB it self. Figure 3:(a) Single-phase equivalent circuit, (b) Transient recovery voltage [10] Hosny, Ahmed

  7. Arc Quenching Mechanism Figure 4: A Schematic representation of the puffer interrupter indicating some important physical processes. [2] Hosny, Ahmed

  8. Pros & Cons of SF6 • SF6 has a dielectric strength of about two to three times that of air. • It is nontoxic. • It is nonflammable. • It is noncorrosive; it doesn’t react with other materials because it is inert gas. However, when it is heated to 5000C it decomposes and its decomposition products react with other materials. • It exhibits excellent properties for arc quenching. So, it used as an interrupting medium in circuit breakers instead of air or oil. Hosny, Ahmed

  9. SF6 Circuit Breaker Figure 6: SF6 Circuit breaker, 36kV, 4000A, SC 50kA. [12] Figure 5: A plot of the thermal conductivity of SF6 and N2 [11] Hosny, Ahmed

  10. Residual SF6 Plasma Species • Ionization • Associative detachment • Dissociative attachment Table 1: Particle densities of residual SF6 plasma at 3000 K, 105 Pa [1] Hosny, Ahmed

  11. Electron Velocity Distribution Function Normalization Factor Collision frequency Energy loss due to collisions Hosny, Ahmed

  12. SF6CB applications … GIS Advantages of Gas-insulated switchgear (GIS) are: • Compact size. • Totally isolated from the atmospheric conditions such as air pollution, high temperature, snow, etc. • High degree of reliability and safety precaution. •  Easy to install. • SF6 has a dielectric strength much higher than air which is the insulated gas for conventional switchgear type. Figure 7: Gas-insulated substations (the picture shows a typical example) are very compact in size and reliable in operation Hosny, Ahmed

  13. Conclusion • The primary Cause of high transient over-voltage is the generation of multiple re-ignitions during the interrupting period by some types of CB. This TRV are the most likely cause of CB damage. • The design of CB can be determined using the thermal flow characteristics near current zero. • The critical field strength for the breakdown of the residual plasma has been found to be proportional to the pressure and is equal to 2.0V/(m.Pa), which is only ~ (1/45)th of that of SF6 at room temperature. Hosny, Ahmed

  14. Future Work • Further study on calculation of TRV and post-arc current just after current zero. • Advanced arc model and measurement techniques, which can support the physical phenomena in CBs. • Study the theory of positive corona in SF6 due to impulse voltage. Hosny, Ahmed

  15. References • J.D. Yan, M.T.C. Fang and Q.S. Liu, “Dielectric Breakdown of a Residual SF6 Plasma at 3000K under Diatomic Equilibrium”, IEEE Transaction on Dielectrics and Electrical Insulation, Vol. 4 No.1, February 1997. • D.W. Shimmin and et al, “Transient Pressure Variations in SF6 Puffer Circuit breakers”, Applied Physics, 23 (1990) pp. 533-541. • P.H. Schavemaker and L. Van der Sluis, “ The influence of the Topology of Test Circuits on the Interrupter Performance of Circuit Breakers”, IEEE Transaction on Power Delivery, Vol. 10, No. 4, October 1995. • M. T. C. Fang and M. Y. Shent, “A comparative study of two computational methods for the simulation of discharge development in SF6”, Appl. Phys. 28 (1995) 364-370. • Z. Ma and et al, “ An Investigation of Transient Over voltage Generation when switching high voltage shunt reactors by SF6 circuit Breaker”, IEEE Transaction on Power Delivery, Vol. 13, No. 2, April 1998. • Jong-Chul Lee and Youn J. Kim, “ Numerical Modeling of SF6 thermal plasma generated during the switching process”, Science Direct, Elsevier, 2005, pp. 72-80. Hosny, Ahmed

  16. References (Cont.) • Richard Morrow, “ Theory of Positive Corona in SF6 Due to a Voltage Impulse”, IEEE Transaction on Plasma Science, Vol. 19, No. 2, April 1991. • J. D. Yan, M. T. C. Fang and Q. S. Liu, “Dielectric Breakdown of a Residual SF6 Plasma at 3000 K under Diatomic Equilibrium”, IEEE Transaction on Dielectrics and Electric Insulation, Vol. 4, N0. 1, February 1997. • Gerd Duning and Manfred Lindmayer,” Plasma Density Decay of Vacuum Discharge After Current Zero”, IEEE Transaction on Plasma Science, Vol. 27, No. 4, August 1999. • Mazen Abdel-Salam and et al, High-Voltage Engineering: Theory and Practice, Marcel Dekker, Inc., New York, 2000 • http://www.metatechcorp.com/aps/cold_weather_operating_problems_.htm. • http://www.abb.com/global/abbzh/abbzh251.nsf!OpenDatabase&db=/global/seitp/seitp328.nsf&v=9AAC720001&e=us&c=C1256CCB004E3ABBC125699F0042734E. Hosny, Ahmed

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