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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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slide1
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

outline
Outline
  • Introduction
  • Plasma characteristics
  • Advantages and Disadvantages of SF6
  • Residual SF6 plasma species
  • Gas Insulated Switchgear (GIS)
  • Conclusion
  • Future work
  • References

Hosny, Ahmed

slide3

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

slide4

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

slide5

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

plasma power source
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

arc quenching mechanism
Arc Quenching Mechanism

Figure 4: A Schematic representation of the puffer interrupter indicating some important physical processes. [2]

Hosny, Ahmed

pros cons of sf 6
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

sf 6 circuit breaker
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

slide10

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

electron velocity distribution function
Electron Velocity Distribution Function

Normalization Factor

Collision frequency

Energy loss due to collisions

Hosny, Ahmed

sf 6 cb applications gis
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

slide13

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

slide14

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

slide15

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

references cont
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