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Gas circuit breakers with CO2 or air as the interrupting medium
Abstract
SF6 is widely used in high voltage gas circuit breakers because of its high dielectric strength and excellent arc interruption properties and because it is non-toxic and recombines after arcing. SF6 has a high global warming potential, and while it is readily possible to prevent SF 6 from being released to the atmosphere when it is used in gas circuit breakers, alternatives such as synthetic air or CO2 have been proposed. In this work we summarize the results of a study done to assess the arc interruption performance of synthetic air and CO2 using SF 6 as a benchmark. Experiments in simplified test geometries were carried out to measure the arc interruption performance of the two gases under the same conditions. The current-zero phase of the current interruption process in a circuit breaker model is investigated in detail.
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Available data on the electron transport properties and electron swarm coefficients are discussed for the following electronegative gases: SF6, CF4, C2F6, C3F8, C4F10, CCl2F2, O2, air, H2O, CO2, F2, NF3, Cl2, Br2, I2, N2O, NO, HCl, NH3. Graphical presentations comparing measured and calculated data are given for the electron drift velocity, the ratio of diffusion to mobility, the electron attachment and ionization coefficients, and the electron growth constant as functions of E/N, the reduced field strength, for each gas. Graphs of the detachment and excitation coefficients are presented where these data are available. Data originally reported in terms of rate coefficients as functions of mean electron energy are graphically presented in that form. Recommendations concerning reliability are made.
Newly surveyed sets of energy loss cross sections are presented for N2, O2, and O. The work was motivated by a number of new electron energy loss measurements in the late 1980s and early 1990s and recent selected review articles. Each set includes a total ionization cross section and excitation cross sections that correspond to all important non-ionizing energy loss channels for that species. A total cross section for each species is constructed by summing the elastic scattering cross section with the ionization and excitation cross sections. The sum is compared to a measured total cross section obtained from electron transmission experiments. Good agreement is achieved for each of the three species. A loss function is also constructed for each species and compared with the Bethe formula above 100 eV. Good agreement is also achieved in energy loss which is dominated by ion and secondary electron production. Fluxes of photoelectrons and auroral electrons have been calculated for the new sets of energy loss cross sections as well as our previous sets. No substantial differences occur using the new description of energy loss.
The dielectric recovery of an axially blown arc in an experimental set-up based on a conventional HV circuit breaker was investigated both experimentally and theoretically. As a quenching gas, synthetic air was used. The investigated time range was from 10 µs to 10 ms after current zero (CZ). A fast rise in the dielectric strength during the first 100 µs, followed by a plateau and further rise later was observed. The dependences on the breaking current and pressure were determined. The measured dielectric recovery during the first 100 µs after CZ could be reproduced with good accuracy by computational fluid dynamics simulations. From that it could be deduced that the temperature decay in the axis does not depend sensitively on the pressure. The dielectric recovery during the first 100 µs scales therefore mainly with the filling pressure. The plateau in the breakdown characteristic is due to a hot vapour layer from the still evaporating PTFE nozzle surface.
Fluid models of gas discharges require the input of transport coefficients and rate coefficients that depend on the electron energy distribution function. Such coefficients are usually calculated from collision cross-section data by solving the electron Boltzmann equation (BE). In this paper we present a new user-friendly BE solver developed especially for this purpose, freely available under the name BOLSIG+, which is more general and easier to use than most other BE solvers available. The solver provides steady-state solutions of the BE for electrons in a uniform electric field, using the classical two-term expansion, and is able to account for different growth models, quasi-stationary and oscillating fields, electron–neutral collisions and electron–electron collisions. We show that for the approximations we use, the BE takes the form of a convection-diffusion continuity-equation with a non-local source term in energy space. To solve this equation we use an exponential scheme commonly used for convection-diffusion problems. The calculated electron transport coefficients and rate coefficients are defined so as to ensure maximum consistency with the fluid equations. We discuss how these coefficients are best used in fluid models and illustrate the influence of some essential parameters and approximations.
This paper describes the influence of the switchgear geometry, the priming pressure of the SF6 switchgear and the magnitude of the short-circuit current on the dielectric recovery of the arc gap, using the example of a high-voltage circuit-breaker for a 145 kV network. the results of other tests document the influence of the arc-quenching gases nitrogen (N2), carbon dioxide (CO2) and a nitrogen/SF6 mixture on the arc gap recovery in comparison with SF6. the results show that the arc control capability of these gases is very limited compared with SF6. Consequently, it will not be possible totally to replace the SF6 in high-voltage switchgear in the short to medium-term.
SF6 gas has widely been used for high-voltage and large-capacity electric power equipment such as gas insulated switchgears (GIS) and gas circuit breakers (GCB) due to its excellent insulating and arc-quenching capability. Although SF6 gas strongly contributes to achieve compactness and high reliability of the equipment, it has been recognized as one of the potent greenhouse gases and was designated to reduce the emissions at COP3 at Kyoto in 1997. At present, strategic effort to reduce the emissions is being made, which actually pan out.1 Over the long term, however, it is certainly preferable to reduce the consumption itself, because its atmospheric life time is observed to be quite long, thus the amount of SF6 gas on the earth will inevitably get increasing in the future unless artificial destruction.
It is widely accepted that the simplified streamer breakdown criterion
(1)
where is the effective coefficient of ionization, x is a coordinate along an electric field line and K is a dimensionless number representing various secondary ionization process, can well be used to calculate breakdown voltages in many gases subjected to homogeneous or weakly inhomogeneous field distributions. For field distributions of this kind, x
c
is either identical with the gap distance ( g) or a critical electron avalanche length, which is defined by a position within the gap, where . Though K is often taken to be 18 for calculating onset of breakdown ( thus taken to be the natural logarithm of a critical number Ncrit of about 108, assumed as a number of electrons produced by ionization in a critical avalanche), it has been shown by A. Pedersen et. al.1 and W.S. Zaengl et. al.2 that K for SF6 and synthetic air is much lower.
The dielectric recovery in high-voltage circuit breakers after interruption of high-current amplitudes was investigated experimentally in a test device. Various current amplitudes were tested, which cover a typical range of practical interest. Simulations with computational fluid dynamics together with electric field simulations allowed one to deduce the physical parameters in the region where the breakdown was decided. A leader inception model using these parameters explains under which condition leader inception occurs; causing breakdown of the gap. Based on this model scaling laws for leader inception are given.
The development and optimization of circuit breakers is nowadays strongly influenced by computational fluid dynamics (CFD) simulations. The main reason is that the corresponding experiments are expensive and provide only limited amount of data, usually in integral form. On the other side, CFD allows analyzing the transient behavior of all quantities described in the models. This contribution collects a number of CFD related activities for circuit breaker research and development at ABB Corporate Research. In the simulations reported here, the plasma is treated as a one fluid model, i.e. the molecular processes such as dissociation and recombination are only reflected by pressure and temperature dependent material properties. The paper introduces the CFD model with radiation transport and the coupling to the electro- and magneto-static field equations. The predictive power of these simulations is demonstrated through comparison with results from a small scale test device (mixing of hot gas in a heating volume) and a full breaker (arc voltage and pressure rise).
It has been observed in our tests that the post arc current near the breaking limit of a CO2 circuit breaker is 10 A or more, and the post arc current of a SF6 circuit breaker is approximately 0.3 A. We explain this major difference in the post arc current with calculations using two serially-connected arc models. We prove that the arc characteristic of a relatively longer time domain up to the extinction peak for a CO2 circuit breaker and that of a short time domain from the extinction peak until the current zero point for a SF6 circuit breaker have great effects on breaking performance.
We investigated the fundamental characteristic of CF3I as a substitute gas for SF6. CF3I has lower global warming potential. The use of pure CF3I in gas-insulated switchgear and gas circuit breakers is difficult because liquid CF3I has a high boiling point. We therefore mixed CF3I with CO2 or N2. In short line fault (SLF, 1 kApeak) and breaker terminal fault (BTF, 3 kApeak) interruption, the performance of CF3I¿CO2 approximated that of pure CF3I when the proportion of CF3I exceeded 30%. However, for BTF (20 kApeak) interruption, the performance of CF3I¿CO2 remarkably decreased. In loop current interruption for disconnecting switches, CF3I¿CO2 (30%/70%) was successfully used 200 times for 4000 A. We also measured CF3I spectra. Investigation of the decomposed gas density after current interruption revealed that fluorine release from CF3I was less than that from SF6. Iodine density released from CF3I-CO2 (30%/70%) was approximately one-third of that released from pure CF3I. In addition, iodine could be removed using an adsorbent.
Power system engineering largely focuses on steady state analysis. The main areas of power system engineering are power flow studies and fault studies - both steady state technologies. But the world is largely transient, and power systems are always subject to time varying and short lived signals. This technical report concerns several important topics in transient analyses of power systems. The leading chapter deals with a new analytical tool-wavelets-for power system transients. Flicker and electric are furnace transients are discussed in Chapters I1 and IV. Chapter 111 deals with transients from shunt capacitor switching. The concluding chapters deal with transformer inrush current and non simultaneous pole closures of circuit breakers. This report was prepared by the students in EE532 at Purdue University. When I first came to Purdue in 1965, Professor El-Abiad was asking for student term projects which were turned into technical reports. I have 'borrowed' this idea and for many years we have produced technical reports from the power systems courses. The students get practice in writing reports, and the reader is able to get an idea of the coverage of our courses. I think that the students have done a good job on the subject of transients in power systems.
An accurate and robust method for radiative heat transfer simulation for arc applications was presented in the previous paper (part I). In this paper a self-consistent mathematical model based on computational fluid dynamics and a rigorous radiative heat transfer model is described. The model is applied to simulate switching arcs in high voltage gas circuit breakers. The accuracy of the model is proven by comparison with experimental data for all arc modes. The ablation-controlled arc model is used to simulate high current PTFE arcs burning in cylindrical tubes. Model accuracy for the lower current arcs is evaluated using experimental data on the axially blown SF6 arc in steady state and arc resistance measurements close to current zero. The complete switching process with the arc going through all three phases is also simulated and compared with the experimental data from an industrial circuit breaker switching test.
The average surface ablation of poly-tetra-fluro-ethylene (PTFE) nozzles in high voltage circuit-breakers was investigated experimentally by means of the specific ablation. Experiments were done with a test device in the current and arcing time range of 2–40 kArms and 5–17 ms, respectively. This allowed determining the dependences of the specific PTFE ablation on current and arcing time. Additionally, the specific PTFE nozzle ablation in commercial high voltage circuit-breakers was analysed in a broad range of current amplitudes and arcing times. For understanding the results more in detail, experiments with a small scale test device were performed. The different experiments yielded consistent values for the PTFE ablation. The ablation depends mainly on the total arc energy. The total ablation is given by the ablation of walls surrounding the arc and by the ablation in regions where plasma from the arc cools down. Different specific ablation values can be observed for the axial blown arc mode and the ablation controlled arc mode.
A model for the axially blown cylindrical arc is derived. In contrast to earlier theories, the model is gauge invariant with respect to energy, which is crucial for investigating current interruption. We determine from our model the dependence of the maximum interruptible current rate, (dI/dt)L , on the pressure, on the parallel capacitance, and on the line impedance for an SF 6 arc. (dI/dt)L scales, approximately independent of the gas type, with the square root of the pressure. The arc resistance, at current zero with current rate equal to (dI/dt)L , is pressure independent. As a consequence, the arc resistance at current zero can serve as a figure of merit for the interruption performance of gas circuit breakers.
This document is the user`s manual for the third-generation CHEMKIN package. CHEMKIN is a software package whose purpose is to facilitate the formation, solution, and interpretation of problems involving elementary gas-phase chemical kinetics. It provides a flexible and powerful tool for incorporating complex chemical kinetics into simulations of fluid dynamics. The package consists of two major software components: an Interpreter and a Gas-Phase Subroutine Library. The Interpreter is a program that reads a symbolic description of an elementary, user-specified chemical reaction mechanism. One output from the Interpreter is a data file that forms a link to the Gas-Phase Subroutine Library. This library is a collection of about 100 highly modular FORTRAN subroutines that may be called to return information on equations of state, thermodynamic properties, and chemical production rates. CHEMKIN-III includes capabilities for treating multi-fluid plasma systems, that are not in thermal equilibrium. These new capabilities allow researchers to describe chemistry systems that are characterized by more than one temperature, in which reactions may depend on temperatures associated with different species; i.e. reactions may be driven by collisions with electrons, ions, or charge-neutral species. These new features have been implemented in such a way as to require little or no changes to CHEMKIN implementation for systems in thermal equilibrium, where all species share the same gas temperature. CHEMKIN-III now has the capability to handle weakly ionized plasma chemistry, especially for application related to advanced semiconductor processing.
Proper combination of fast, high-resolution analogue to digital converters, optical signal transfer and digital signal processing tools with advanced current and voltage measurement sensors has led to the development of a compact current zero measurement system for application in high-power laboratories as an aid in testing SF6 circuit breakers. The application of this system in the renovated high-power laboratory of Toshiba Co is described, including the results of short-line fault tests in the range 16-70 kA on a 300 kV single break model circuit breaker. Three levels of information on the 'quality of interruption', obtained from current zero measurements are discussed: (1) direct observation of post-arc current, arc voltage collapse phenomena, commutation process of arc current into (stray-) capacitance etc.; (2) the arc conductivity very shortly (200 ns) before current zero, an indicator of the performance of the breaker under test. A new quantitative method of electrical endurance mapping is presented; and (3) arc model parameters are extracted out of every individual test, that enable prediction of the performance under other conditions than those tested (e.g. with an internal capacitor).
One important requirement for circuit breakers when interrupting, short line fault currents is their ability to withstand the initial rise of the recovery voltage immediately after current zero. For gas flow breakers this capability is limited by the thermal recovery speed oI tne gas. The measured relative thermal recovery performance of various gases and their mixtures are reported. They differ by more than four orders of magnitude. Some of the gases have been selected because of their possible candidacy for application. Others because of the expeotid effect of their ditterent gas parameters on interruption performance. An attempt has been made to correlate specific mass dependent thermodynamic and kinetic parameters of the gases to their thermal interruption performance.
SF6 gas has excellent dielectric strength and interrupting capability and is used in various applications such as gas insulated switchgear (GIS) in substations. However, since SF6 has a high global warming potential (GWP), it is imperative to reduce its use and develop recovery technology for its reuse. This paper examined the potential of alternative insulating gases for GIS, determining experimentally the ac and lightning impulse breakdown characteristics of CO2 and N2 gases, which have little environmental impact, in a quasi-uniform electric field. The effect of electrode surface roughness is greater in N2 than in CO2. The impulse ratio in a quasi-uniform electric field was smaller in N2 than in CO2 at low pressure, but this reversed when the pressure reached 1.2 MPa. The dielectric strength of an electrode with a dielectric coating was approximately equal to that of a specular-finish bare electrode in either CO2 or N2 when an ac voltage was applied. When lightning impulse voltage was applied, a significant improvement of dielectric strength was observed if a dielectric coating was applied to the electrode considered to be the initial electron source.
SF6 gas has been widely used in arc interruption applications for the past 20 years. Reported here is a systematic, comprehensive effort to search for and evaluate gases and gas mixtures suitable as an arc interruption medium potentially superior to SF6. The search began with several hundred gases, narrowed down to about forty, and finally fifteen gases and gas mixtures were evaluated in a full size puffer-type interrupter under 60-Hz high-power conditions. The results showed SF6 stood out as having the best interruption ability with several mixtures having ~80 percent of SF6' s performance.
An experimental and theoretical study on ablation controlled arcs in cylindrical tubes is presented. Measuring techniques for stagnation pressure, electric field strength, mass ablation rate, and arc cross section are described with which a comprehensive set of experimental data is obtained for blackened PTFE as a reference material. These data are interpreted with an isothermal two-zone model that consistently accounts for the balance of mass and axial momentum and yields simple scaling laws for the arc characteristics. Consistent agreement with the experimental data is found for an arc temperature TA = 19 000 ± 2000 K, a vapor layer temperature Tv = 3400 ± 200 K, and a transparently radiated fraction of the arc power of v = 0.32 ± 0.03. The vapor temperature can be explained with a photoablation mechanism. The ablation arc model allows quantifying of the phenomena related to nozzle clogging in gas-blast circuit breakers, namely flow blocking and reverse flow heating. How these phenomena determine the pressure rise in self-blast circuit breakers is shown.
The results are presented of a model experiment to investigate the dielectric recovery of an axially blown sulphur hexafluoride (SF6) arc after current zero. With the aid of Schlieren pictures and interferometry, the temperature decay after current zero is observed up to the point of complete recovery of the gap. The dielectric recovery is directly measured by applying voltage pulses across the gap which causes breakdown at different times after current zero. Residual charges, which play a role in the early recovery phases, are detected using a specialiy developed technique. Variations of the shape of the voltage pulses and the geometry cause characteristic changes of the recovery, which support the interpretation of the experimental data.
This paper describes a consistent set of thermodynamic properties and transport coefficients for different gases and gas mixtures depending on temperature and pressure. The species thermochemical properties have been computed directly from their partition functions. Atomic and molecular energy levels have been incorporated up to 50.000 K avoiding extrapolation of the JANAF data. Equlibrium particle densities are shown for pure PTFE (C 2 F 4 ) and selected gas mixtures of PTFE, SF 6 and N 2 . From the equilibrium calculations, the system thermodynamic properties (Gibbs and Helmholtz energies, specific enthalpy and internal energy) are obtained directly. The derivatives of these quantities (c p , c v , velocity of sound and adiabatic coefficient) have been calculated using an essentially exact numerical calculation of both the frozen and reaction parts, avoiding numerical differentiation. The calculation of the transport properties like viscosity, electrical and thermal conductivity is b...
Evaluation of interruption capability on various gases
- K Mochizuki
- T Ueno
- H Mizoguchi
- S Yanabu
- S Yuasa
- S Okabe
K. Mochizuki, T. Ueno, H. Mizoguchi, S. Yanabu, S. Yuasa, and
S. Okabe, "Evaluation of interruption capability on various gases,"
in Gaseous Dielectrics X. New York, NY, USA: Springer-Verlag, 2004,
pp. 265-272.
Alternating-Current Circuit-Breakers, IEC Standard 62271-100
- High-Voltage
- Switchgear
- Controlgear
High-Voltage Switchgear and Controlgear-Part 100: Alternating-Current Circuit-Breakers, IEC Standard 62271-100, Apr. 2008.
Compilation of Electron Cross-Sections
- A V Phelps
A. V. Phelps. (2008). Compilation of Electron Cross-Sections
[Online]. Available: http://jila.colorado.edu/~avp/collision_data/ele
ctronneutral/electron.txt
degrees in engineering-applied science from Lawrence Livermore National Laboratory
- C Patrick
- T X Austin
- M S D Ph
Patrick C. Stoller received the B.S. degree in
physics from the University of Texas at Austin,
Austin, TX, USA, and the M.S. and Ph.D. degrees
in engineering-applied science from Lawrence Livermore National Laboratory, University of California,
Davis, CA, USA, in 1997, 2000, and 2002, respectively.
He has been with ABB Switzerland, Ltd., ABB
Corporate Research Center, Baden-Dättwil, Switzerland, since 2008.
Since 2000, he has been with ABB Corporate Research, Baden-Dättwil, Switzerland. Dr. Seeger has been a member of CIGRE WG 13.04 and the Swiss IEC TC 42. He is member of the Current Zero Club
- Martin Seeger
Martin Seeger (M'04-SM'07) received the
Diploma and Ph.D. degrees in physics from the
University of Heidelberg, Heidelberg, Germany, in
1987 and 1990, respectively.
He has been with ABB Switzerland, Ltd.,
since 1993, in different positions in high voltage
switchgear. Since 2000, he has been with ABB
Corporate Research, Baden-Dättwil, Switzerland.
Dr. Seeger has been a member of CIGRE WG
13.04 and the Swiss IEC TC 42. He is member of
the Current Zero Club, where he is a Chairman of
the Gas Inner Circle.