IEEE TRANSACTIONS ON PLASMA SCIENCE, VOL. 40, NO. 8, AUGUST 2012 2035

Arc Movement Inside an AC/DC Circuit BreakerWorking With a Novel Method of Arc Guiding:

Part II—Optical Imaging Method andNumerical Analysis

Malik I. Al-Amayreh, Harald Hofmann, Ove Nilsson, Christian Weindl, and Antonio R. Delgado

Abstract—This paper aims at understanding the design conceptand behavior of the ionized gases inside a new electrical contactor.The switching device is designed for ac and dc operations up to3.5 kV and nominal currents up to 800 A. The contactor consists offive electrodes: two anodes, two cathodes, and a moving electrodeor bridge which works as an anode and a cathode simultaneously.In order to increase the safety, the electrical contactor includestwo contact points. The line current can be diverted into an arcbetween the electrode and the bridge and an arc between the run-ner electrodes. The movement of the ionized gases is controlled bytwo permanent magnets and two coils installed near the electrodes.The arc plasma itself feeds the coils with current. The arc plasmavelocity increases if more current is allocated in the arc plasma.The dynamics of ionized gases in the contactor is analyzed usingtwo optical methods, viz., optical imaging method and high-speedcamera (HSC). The optical imaging software has been developedto generate dynamic images of the high-speed ionized gases at arate of 50 000 frames/s. The results of this method have been com-pared with those obtained using an HSC. A transient numericalmodel has been developed to simulate the arc plasma inside themain runner for the case of dc current. The properties of the airplasma are considered variable with temperature and pressure.The calculation shows the position and temperature of the arcplasma as a function of time.

Index Terms—Arc plasma simulation, electrical contactor,optical imaging method.

NOMENCLATURE

�A Vector magnetic potential (in volt seconds permeter).

�B Magnetic flux density (in teslas).

Manuscript received December 22, 2011; revised March 12, 2012; acceptedMay 8, 2012. Date of publication June 18, 2012; date of current versionAugust 7, 2012. This work was supported by the Bayerische Forschungsstiftungunder project AZ 746-07.

M. I. Al-Amayreh and A. R. Delgado are with the Institute of FluidMechanics (LSTM), Friedrich-Alexander University of Erlangen–Nuremberg,D-91058 Erlangen, Germany (e-mail: malik.amayreh@lstm.uni-erlangen.de;Antonio.Delgado@lstm.uni-erlangen.de).

H. Hofmann and C. Weindl are with the Institute of Electrical PowerSystems, Friedrich-Alexander University of Erlangen–Nuremberg, 91058Erlangen, Germany (e-mail: hofmann@eev.eei.uni-erlangen.de; weindl@eev.eei.uni-erlangen.de).

O. Nilsson is with Schaltbau GmbH, D-81829 Munich, Germany (e-mail:nilsson@schaltbau.de).

Color versions of one or more of the figures in this paper are available onlineat http://ieeexplore.ieee.org.

Digital Object Identifier 10.1109/TPS.2012.2200698

cP Specific heat (in joules per kilogram kelvin) .�D Dielectric displacements (in ampere seconds per

square meter).�E Electrical field (in volts per meter).�F Lorentz force (in newtons).I Current (in amperes).�j Electric current density (in amperes per square

meter).H Magnetic field intensity (in amperes per meter).k Thermal conductivity (in watts per meter kelvin).N Number of turns.P Pressure (in pascals).P0 Atmospheric Pressure = 101.325 kPa.q Electric charge density (in coulombs per cubic

meter).R Electrical resistance (in ohms).Rspecific Specific gas constant (in joules per kilogram

kelvin).Rm Magnetic reluctance (in ampere-turns per weber).r Covered distance of the arc plasma (in millimeters).T Temperature (in kelvins).To Ambient temperature = 300 K.t Time (in seconds).Δt Time required for the arc plasma to move from a

point to another (in milliseconds).Ui Cartesian velocity components where i = 1, 2, 3.Varc Velocity of the arc plasma (in meters per second).xi Cartesian coordinates (x, y, z)Greek Symbolsρ Fluid density (in kilograms per cubic meter).α Stefan–Boltzmann constant (α = 5.67057 ∗

10−8 W · m · K−4).μ Dynamic viscosity (in newton seconds per square

meter).μ0 Magnetic permeability of free space (μ0 = 4π ×

10−7 N · A−2).μm Magnetic permeability (in newtons per square

ampere).φ Electrical potential (in volts).ε Permittivity of free space (ε ≈ 8.8541× 10−1 F ·

m−1).σ Electrical conductivity (in siemens per meter).δij Kronecker’s delta (δij=1 if i=j and δij=0 if i �=j).

0093-3813/$31.00 © 2012 IEEE

2036 IEEE TRANSACTIONS ON PLASMA SCIENCE, VOL. 40, NO. 8, AUGUST 2012

Fig. 1. Illustration of the new contactor model.

Abbreviationsac Alternating current.CAD Computer-aided design.CV Control volume.dc Direct current.HSC High-speed camera.FFT Fast Fourier transform.

I. INTRODUCTION

THE OPTICAL imaging and numerical analysis are inves-tigated in this paper which is a follow-up to the experi-

mental work in Part I. The electrical contactor under discussionin this paper was designed for the use in ac and dc railwaynetworks. The possibility for both ac and dc operations is verymuch in demand for the interoperability, i.e., when the trainsgo through countries with different operating system, ac, or dc.This was accomplished using a new blowout technique combin-ing permanent magnets and electromagnetic blowout coils. Thesingle-pole contactor enables switching of both extremely lowand very high loads and can also be used in several industrialapplications. The breaker contacts are separated from eachother, thus allowing an electrical potential difference betweenthe contacts, which leads to the establishment of arc plasma[Part I]. The applied magnetic field forces the arc plasma tomove in a certain path or runner until it is finally divided bysplitting plates as shown in Fig. 1.

An effective electrical contactor should be able to decreasethe switching time as well as the thermal stresses of the arcplasma on the electrodes and the splitter plates. One techniquetoward achieving this goal is to elongate the arc plasma in thedivergence runners of the contactor [2]. Other methods involvestretching of the arc plasma between splitting plates [3], [4].Use of many splitter plates leads to a reduction of thermalstresses inside the body of the contactor [5]. The fast blowoutof the ionized gas can be achieved by using external magneticfield sources such as the magnets and the coils. The formercase was studied in detail by Lindmayer and Springstubbe [6],where a simple model of two parallel ferromagnetic materialsadhered to the arc chamber. The metallic vapor and gassingmaterial of the electrodes decrease the temperature and thermal

stresses of the arc plasma [7]. In this paper, the arc plasmafeeds the coils with current, which means that a part of the arcplasma energy dissipates into the coils as a magnetic energy andthermal energy. The desired magnetic field has been generatedusing the coils described in Fig. 1 and in the patent [8]. Themagnetic field accelerates the arc plasma, thus reducing thebreaking times.

As the contactor starts to switch, the bridge in the middle ofthe contactor moves downward. Consequently, the current flowsbetween these electrodes due to the arc plasmas establishedat contact points 1 and 2. The first arc moves along line 1between electrode A1 and the bridge and then between theelectrode B1 and the bridge until it finally elongates betweenB1 and B2 to continue its path to the splitter plates. It should benoted that there is no current in the coils, when the arc is onlyburning between electrodes A1/A2 and the bridge. During thearc motion between plates B1 and B2, a current passes throughthe coil 1 then the coil 2. This would induce a magnetic fieldnormal to the flow direction of the arc. The second arc plasmamoves along line 2, as shown in Fig. 1, and dies out as the bridgegets zero current.

Recently, many methods have been developed to study themovement of ionized gases. Optoelectronic devices were usedto study the movement and structure of the arc plasma insidethe divergence region of the electrical breaker [2] or insidenarrow insulating channels [4]. The root of the arc plasma inlow-voltage electrical contactors was successfully visualizedusing this method [9]. Measuring the electric arc inductionusing Hall-effect probes is another option to study the dynamicbehavior of the arc [5]. Similarly, HSCs are another optical di-agnostic method used by many authors [10]–[12]. In the presentstudy, an optical imaging method has been used in additionto the HSC to visualize the movement of the ionized gasesbetween the five electrodes inside the body of the contactor.

The thermal arc plasma heats the contact material after manyshots with a high repetition rate that produces a microscopicdamage of the contact surfaces. Sometimes, the contacts weld,thus causing damage to the contactor [13]. The design of theelectrical contactor incorporates the use of two contact points.In case that one of the contacts welds, the electrical contactorstill continues to work.

II. OPTICAL IMAGING METHOD

With the purpose to study the movement of the arc plasma inthe body of the contactor, 112 holes were drilled into one side ofthe contactor. Fig. 2(a) shows a map of the holes and the fiber-optic heads, whereas Fig. 2(b) shows these fiber-optic headsembedded in the body of the contactor. The light is convertedinto an electrical signal using a photodetector amplifier circuitexplained and shown in Fig. 3. The illumination of the siliconphotodiode causes a current to flow through the amplifier’scircuit. Resistance R3 prevents the photodetector amplifier’scircuit from overload in the case of high-energy plasma arcs.The photodiode circuit in Fig. 3 was calibrated by supplyinga fixed-amplitude light pulse to the photodiode. The outputvoltage was adjusted using the variable resistance R1 to seta level equal to the amplitude of the inlet light pulse. This

AL-AMAYREH et al.: ARC MOVEMENT INSIDE AN AC/DC CIRCUIT BREAKER—PART II 2037

Fig. 2. Map of the hole numbers and the fiber-optic heads inside the body of the contactor. (a) Shaded holes filled with fiber-optic heads. (b) Thirty-two fiber-opticheads embedded inside the contactor.

Fig. 3. Fiber-optic head through the walls of the contactor connected to the photodiode circuit. r = 4 mm, R2 = 2 kΩ, R3 = 5 kΩ, R4 = 1 kΩ, R5 = 2 kΩ,C2 = 100 nF, and C1 = 100 μF.

procedure was repeated for all the photodiodes. The photodiodesignals are recorded by a National Instruments data acquisitiondevice at a sample rate of 50 kHz. A LabVIEW program hasbeen developed to control the work of all the sensors and thestorage of the data. A C++ software has been developed topostprocess the optical readings which yield the positions andlight emissions of the ionized gases. The HSC is capable ofcapturing 10 000 frames/s and fixed in front of the contactor(for more details refer to Part I).

III. RESULTS OF THE OPTICAL METHODS

The optical imaging and the HSC results are shown inFigs. 4–7 for the case 280 A ac and 3.5 kV. The curves of thebreaking current and voltage as a function of time alongsidethe calculation of the arc speed for this example were discussedin Part 1. The optical imaging results present the strength ofthe signals measured by the photodiodes, and the HSC resultsshow the light from the arc shining through the drilled holes.Fig. 4(b) shows that the right and left arc plasmas are ignitednear to the holes 144 and 190, respectively. The gray-scale barshows that the light emission ranges from black shades (no

emission) to white shades (high emission). The magnetic fieldin this contactor base arises due to the magnets. The magneticfield is applied perpendicular to the plasma field and is shownin the simplified model [Fig. 4(a)]. The right arc plasma movestoward the vertical runner, whereas the left arc plasma movesout of the contactor. As the right arc plasma in Fig. 5 reaches thebeginning of the vertical runner (i.e., when the right arc appearsbetween the bridge and the electrode B1), the current appearsin coil 1. In addition, the arc plasma shows an oscillation inthis region. Then, the right arc plasma, which appears in Fig. 6between the electrodes B1/B2, carries the current between theseelectrodes. Consequently, the current passes between the twocoils. The crescent arc plasma in Fig. 7 shows an elongationbefore reaching the splitter plates.

The previous example shows that the contactor can be usedfor ac currents. Next paragraphs illustrate an example for casedc current to show the calculation of arc speed. Later in thispaper, these results will be compared with the numerical results.The curves of the arc current and arc voltage for this exampleappear in Fig. 8 for an operating current of 750 A and voltage of400 Vdc. The ignition occurs at the time 41 ms, and the currentappears in the first coil then in the second coil.

2038 IEEE TRANSACTIONS ON PLASMA SCIENCE, VOL. 40, NO. 8, AUGUST 2012

Fig. 4. Ignition of the arcs for case line current of 280 A ac and 3.5 kV at t = 78.1 ms. (a) Arc plasma in the contactor base. (b) Optical imaging results.(c) HSC results.

Fig. 5. Movement of the right arc plasma from the contactor base to the vertical runner for case line current of 280-A ac and 3.5 kV at t = 82.2 ms. (a) Deflectionof the right arc. (b) Optical imaging results. (c) HSC results.

Fig. 6. Right arc plasma runs between the electrodes B1/B2 for case line current of 280 A ac and 3.5 kV at t = 82.6 ms. (a) Right arc between electrodes B1/B2.(b) Optical imaging results. (c) HSC results.

Fig. 7. Elongation of the right arc plasma for case line current of 280 A ac and 3.5 kV at t = 82.9 ms. (a) Arc lengthening. (b) Optical imaging results. (c) HSCresults.

The signals of four photodiodes measured along the center-line of the contactor are shown in Fig. 9. It should be noted thatthese results display the first arc ignition within this switchingprocess. Also, all curves are filtered with FFT low-pass filter todecrease the noise. The arc speed can be calculated as

Varc =r

Δt(1)

where r is the covered distance by the arc plasma; in thisexample, r is the distance between the two fiber-optic heads.Δt is the shift time between the peaks of the curves thatare marked in Fig. 9. The arc speed calculation results inTable I show an acceleration of the arc plasma along thecenterline.

The velocity of the arc plasma increases if more current isallocated in the arc plasma and the coils, since the Lorentz force

AL-AMAYREH et al.: ARC MOVEMENT INSIDE AN AC/DC CIRCUIT BREAKER—PART II 2039

Fig. 8. Measured currents in the coils, arc plasma, and the arc voltage for750 A/400 Vdc.

Fig. 9. Example used to show the calculation of the arc plasma speed betweenselected fiber-optic heads for 750 A and 400 Vdc.

TABLE ICALCULATION OF THE ARC PLASMA SPEED FOR CASE LINE CURRENT

750 DC AT 400 Vdc

is proportional to the current. The results for different currentloads are shown in Table II, where the velocity of the arc plasmaVarc_152,153 was measured between the two fiber-optic heads152 and 153.

IV. MODELING AND DISCRETIZATION

The flow of ionized gases and heat transfer inside the verticalrunner of the contactor are governed by Maxwell’s equationsand the compressible Navier–Stokes equations [14]–[17], [23].Some simplifications were considered in order to simulate theplasma. The mathematical model does not consider the ablationof the contact material, and the air plasma is assumed to be in alocal thermodynamic equilibrium. The governing equations canbe represented in differential form as

ζ

[∂(ρΦ)

∂t+

∂(ρUiΦ)

∂xi

]=

∂

∂xi

(ΓΦ

∂Φ

∂xi

)+QΦ (2)

where ζ and Φ represent the transported quantities in eachequation, ΓΦ is a diffusion coefficient, QΦ is a distributed

source, and i, j, k = 1, 2, 3. The values of these variables ineach equation are summarized in Table III, where Fj is theLorentz force �j × �B.

The heat radiation Qradiation defined by Karetta andLindmayer [16] is given as

Qradiation = 4αk̃(T 4 − T 4

o

)(3)

where k̃ = 13 [m−1] · p · p−10 is the absorption coefficient. The

viscous dissipation Qdissipation is given by

Qdissipation = μ

(∂Uj

∂xi+

∂Ui

∂xj− 2

3δij

∂UK

∂xK

)∂Ui

∂xj. (4)

The resistive heating or ohmic heating is the energy spentthrough the arc written as

Qohmic = �j • �E. (5)

The equations governing the electric and magnetic fields arethe Maxwell’s equations which are

∇× �E = − ∂ �B

∂t(Faraday’s law) (6)

∇× �H =�j +∂ �D

∂t(Ampere’s law) (7)

∇ • �D = q (Poisson’s law) (8)

∇ • �B =0 (9)

where

�D = ε �E and �B = μ �H.

In this mathematical model, the displacement current in Am-pere’s law ∂ �D/∂t and the electric charge density q in Poisson’slaw are neglected [18]. These simplifications in Maxwell’sequations often are considered for describing a low-frequencyphenomenon [19]. Ohm’s law can be used to calculate thecurrent density inside the ionized gas fluid flow

�j = σ( �E + �U × �B). (10)

The relation between the electrical potential φ and the elec-trical field �E is written as

�E = gradφ. (11)

The current continuity is the divergence of the current density

div�j = 0. (12)

The vector magnetic potential �A correlates with the magneticinduction flux �B as follows:

�B = curl �A. (13)

2040 IEEE TRANSACTIONS ON PLASMA SCIENCE, VOL. 40, NO. 8, AUGUST 2012

TABLE IISPEED OF THE ARC PLASMA BETWEEN THE OPTICS 152 AND 153 ALONG THE CENTERLINE

FOR DIFFERENT DC CURRENTS AND A VOLTAGE OF 400 Vdc

TABLE IIIDESCRIPTION OF THE QUANTITIES AND SOURCES USED IN (2)

Fig. 10. Mathematical model. (a) Structural grid and the coordinates. [(b)–(f)] Boundary conditions used in the mathematical model.

The magnetic field �H and the magnetic vector potentialrelation can be written as

curl �H = curl

[1

μocurl �A

]= σ grad φ+ σ(�U + �B). (14)

The resistance of the arc is Rarc = h/∫Sa

σds, where h isthe separation distance between the electrodes B1/B2 and Sa

is the section corresponding to the conducting zone [17]. Theequation of state is given in the form

P = ρRspecificT. (15)

The thermodynamic coefficients of thermal plasma arevery sensitive to the temperature and pressure. In this paper,the thermodynamic and transport properties are defined as afunction of temperature and pressure and obtained from [1]and [20].

Fig. 11. Average arc voltage drop and average currents in the coils are takenfrom the experiments as input data for the numerical model.

The mathematical model described earlier has been solvedusing the finite volume method. This method transforms thepartial differential equations into linear continuous equations

AL-AMAYREH et al.: ARC MOVEMENT INSIDE AN AC/DC CIRCUIT BREAKER—PART II 2041

Fig. 12. Simplified magnetic circuit. (a) Description of the magnetic circuit. (b) Magnetic field calculated from the magnetic circuit for case 750 A at 400 Vdc.

and enables to solve even complex geometries. The geometryof the calculation domain was generated in the CAD programProEngineer. Fig. 11 shows the calculation domain which isdivided into about 350 000 structured hexahedral cells; each cellrepresents a CV, and all the cells describe the geometry of thecontactor. The complex geometry in the base of the contactorhas not been included. The 3-D domain has been discretizedusing the program ANSYS ICEM. The computational model isdivided into 22 blocks to handle the geometry. The commercialCFD program ANSYS CFX [21] has been used to solve the sys-tem of partial differential equations with Fortran subroutines toimplement the sources. The shear stress transport k − ω-basedmodel was used to simulate the turbulent flow and near walls[21], [22]. The high-resolution advection scheme is applied inthe computations.

As shown in Fig. 10, adiabatic and no-slip conditions areassumed at the walls. Zero static pressure and the average of thetemperature are considered in the case of opening conditions,whereas a zero electric field flux is defined at the nonmetallicwall. Furthermore, it is assumed that the ignition position isat the lower point between the electrodes B1/B2. A voltagedrop is given between the electrodes B1/B2 to treat the transferof current [23]. The arc voltage drop and currents in the coilsare taken from the experiments as input data for the numericalmodel. In order to smoothen the experimental data, about16 experimental results are averaged for a current of 750 Adc and a voltage of 400 V. These curves are shown in Fig. 11.The external magnetic field is applied in the z-direction andperpendicular to the symmetry plane.

All computations involved in this study were performed byusing 16 parallel processors. To start with, the task was solvedas a steady-state calculation with zero external magnetic fields.This steady-state case was, in turn, used as an initial conditionfor the unsteady case. The computing time for the unsteadysolution was 11 h.

The external magnetic field imposed in the plasma domain isgenerated by the permanent magnets and the two coils. With theaim of generating a more homogeneous magnetic field whichis acting perpendicular to the plasma domain, the coils andthe magnets were connected with pole plates [see Fig. 12(a)].Without operational current, a constant magnetic field fromthe permanent magnets was measured with a Gauss meter to

Fig. 13. Numerical calculation of the temperature profiles along the centerlineat different times.

Fig. 14. Comparison between the numerical and experimental results of thearc speed along the centerline for 750 A and 400 Vdc.

be 12 mT at contact points 1 and 2, as shown in Fig. 1. Themagnetic fields from the coils change with the coil current.Fig. 12(a) shows a coil of 200 turns and a magnetic core ofmean length L = 44 mm and diameter D = 16 mm. The coreof the coil is connected to two pole plates. The distance betweenthe pole plates is the length of the coil core. This system canbe modeled as a simplified magnetic circuit. Assuming that thesize of the device and the operation frequency are such thatthe displacement current in Maxwell’s equations is negligible,the magnetic flux in webers can be written as

φm = BgapAgap =NI

2Rm plate +Rm coil +Rm Gap. (16)

2042 IEEE TRANSACTIONS ON PLASMA SCIENCE, VOL. 40, NO. 8, AUGUST 2012

Fig. 15. Temperature and speed contours in the contactor for a line current of 750 A and a voltage of 400 Vdc.

The magnetic reluctance Rm can be calculated from theequation

Rm =L

μmA. (17)

The materials of the plates and the core of the coils are steel.The values of the magnetic permeability μm can be calculatedfrom the magnetic induction current equation

μm =ΔB

ΔH. (18)

The relation between the magnetic field B and the magneticfield intensity H for steel becomes nonlinear for H > 500 A/mas described by the B–H curve in the manufacturer’s datasheet.Fig. 12(b) shows the results of (16) obtained by using thefitting of the coil current in Fig. 11. First, the magnetic fieldis generated by the magnetic circuit of the first coil, and themagnetic field from the magnetic circuit of the second coil isdelayed.

V. RESULTS

A. Mathematical Model Verification

To verify the mathematical model, the arc voltage drop andcurrents in the coils were taken from Fig. 8 as input data forthe numerical model. Fig. 13 shows the temperature profilein the centerline of the contactor which changes with time dueto the propagation of the arc plasma and the decrease of the arccurrent. Assuming that the position of the arc plasma coincideswith the peak of the temperature profile, the velocity of thearc can be calculated from the shift of the peak temperatureposition r in time. It should be noted that the amplitude ofthe temperature profile decreases as the arc plasma moves

along the centerline. The comparison between the numericaland experimental results is shown in Fig. 14, which showsthe speed of the arc plasma at different times for a current of750 A and a voltage of 400 Vdc. The numerical results agreewell with the measurements. These results show that the arcplasma accelerates due to the rise of the magnetic forces.However, the acceleration or the slope of the curve decreaseswith time due to the reduction of the arc current.

B. Arc Plasma Propagation

A visualization of the arc plasma propagation is made inFig. 15, which shows the variation of the temperature contoursat the symmetry plane. The right side of Fig. 15 shows thevelocity distribution at the midplane at different times. Thehighest temperature is seen in the lower point of the verticalrunner at time 43.5 ms with a value of more than 12 500 K.At this particular time, the external magnetic field from thecoils is very low, and the source of external magnetic field isonly from the magnets in the contactor base. The arc plasmatemperature decreases with time due to the decrease of the arccurrent, stretching of the arc, and the cooling by radiant heat.

The transient response of the arc root position to theimposed magnetic field is shown in Fig. 16. The position ofthe arc plasma root is defined by the center of the highesttemperature at the surface of the runners using the followingequation:

ya =

∫∫surface

y • Tdydz∫∫surface

T • dydz . (19)

The magnetic force from the first coil is greater, because thecurrent first appears in that coil. As a result, the vertical position

AL-AMAYREH et al.: ARC MOVEMENT INSIDE AN AC/DC CIRCUIT BREAKER—PART II 2043

Fig. 16. Calculated vertical position of the arc plasma root determined atthe highest temperature at cathode (electrode B2) and anode (electrode B1),respectively.

of the arc root in the anode is higher than that of the arc root inthe cathode. Consequently, the curvature and stretching of thearc plasma increase with time due to the unbalanced appliedmagnetic fields as well as the shape of the electrode runners.

VI. CONCLUSION

Optical imaging software has been developed to generate50 000 frames/s to study the movements of the ionized gases in-side a new electrical contactor. The optical results show that theposition of the plasma arcs inside the body of the contactor canbe controlled by using two coils and two magnets. The resultsclearly indicate that the ionized gases accelerate in the verticalrunner. In addition, the velocity of the arc plasma increases withthe increase of the total current. The optical imaging resultshave been compared with the results of the HSC.

Furthermore, a 3-D numerical study of an industrial electricalcontactor has been carried out. Here, the arc plasma itself feedstwo coils beside the runner with electrical current in orderto generate a magnetic pressure. This pressure moves the arcplasma from the contactor base to the splitter plates. The arcplasma accelerates inside the runner due to the magnetic field ofthe coils. The magnetic field from the first coil is higher than themagnetic field from the second coil, which leads to a curvatureof the arc plasma.

However, the results of the numerical simulations should betaken with caution. Apart from the simplifications assumed inSection IV, the numerical model has neglected the influence ofthe bridge inside the contactor base which works as anode andcathode at the same time. The simulations of the arc plasmacan be improved by studying the ablation and evaporation ofthe contacts. Further experimental and numerical investigationsneed to be carried out in order to examine the factors underlyingthese phenomena. This would lead to a better understanding inthe future.

ACKNOWLEDGMENT

The authors would like to thank H. Weber for the technicalassistance as well as design engineers at Schaltbau GmbH,R. Kralik and A. Ignatov, for help and advice.

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2044 IEEE TRANSACTIONS ON PLASMA SCIENCE, VOL. 40, NO. 8, AUGUST 2012

Malik I. Al-Amayreh was born in Erlangen,Germany, on October 09, 1981. He received theB.S. degree and M.S. degree (with honors) fromthe Department of Mechanical Engineering, Uni-versity of Jordan, Amman, Jordan, in 2004 and2007, respectively. He is currently working towardthe Ph.D. degree at the Institute of Fluid Me-chanics (LSTM), Friedrich-Alexander University ofErlangen–Nuremberg, Erlangen.

In 2007–2008, he was a Lecturer with the En-gineering Technology College, Al-Balqa’ Applied

University, Amman, Jordan. In 2008–2010, he was a Researcher with theLSTM, University of Erlangen–Nuremberg. His research interests include theapplications of the flow-field-ionized gases and gasification of oil shale usingplasma.

Mr. Al-Amayreh is a member of the European Mechanics Society. He was arecipient of the Alexander Mayer scholarship.

Harald Hofmann was born in Nuremberg,Germany, in 1968. He received the Dipl.-Ing.degree in electrical engineering from the Friedrich-Alexander University of Erlangen–Nuremberg,Erlangen, Germany, in 2002.

In the same year, he was recruited by the ModernDrive Technology GmbH as a Design Engineer andbecame the Head of Development in 2005. Since2008, he has been with the Institute of ElectricalPower Systems, Friedrich-Alexander University ofErlangen–Nuremberg. His primary research interests

are electrical measurement engineering, switching behavior of ac/dc circuitbreakers, and novel measurement methods for the estimation of the remaininglifetime of electrical distribution systems.

Ove Nilsson was born in Tavelsjö, Sweden, in 1956. He received the B.Sc.degree in material physics from Umeå University, Umeå, Sweden, in 1980and the Ph.D. degree from the Department of Experimental Physics, UmeåUniversity, in 1986, with a thesis on developing a new hot-wire method for thedetermination of thermal conductivity and heat capacity under high pressure.

From 1987 to 1991, he was a Postdoctoral Researcher with the Universityof Würzburg, Würzburg, Germany, where he continued in the field of thermalphysics. In 1992, he joined the newly founded Bavarian Center of AppliedEnergy Research, Würzburg, where he was an Administration Manager anda Scientist until 1998. After a period as a Sales Manager for Vitec GmbH,Würzburg, he joined Schaltbau GmbH, Munich, in 2001, where he is a ResearchEngineer. The company produces contactors, snap-action switches, connectors,and master controllers.

Christian Weindl was born in Nuremberg,Germany, in 1965. He received the Dipl.-Ing.degree in electrical engineering and the Dr.-Ing.degree (cum laude) from the Friedrich-AlexanderUniversity of Erlangen–Nuremberg, Germany, in1993 and 1999/2000, respectively.

From 1993 to 1995, he was with the High-VoltageTransmission and Distribution Department (GroupSystem Planning), Siemens AG, Erlangen, and since1994, he has been with the Institute of ElectricalPower Systems, Friedrich-Alexander University of

Erlangen–Nuremberg. Since 2005, he has headed an international project inthe field of the artificial aging of power cables and estimation of the remain-ing lifetime of electrical distribution systems. His primary research interestsare harmonic stability, control of converters and FACTS equipment, and theinteractions of these devices with the surrounding network.

Dr. Weindl was a recipient of the Literature Award of ETG/VDE in 1999, andin 2002, his Ph.D. work was a recipient of a research price by a major Germanutility (E-ON Bayern AG).

Antonio R. Delgado was born in Sevilla, Spain,on April 17, 1956. He received the Diploma (withhonors) in process technology and the Dr.-Ing. de-gree (1986) from the University of Duisburg–Essen,Essen, Germany.

In 1987–1992, he was the Head of “Fluid Mechan-ics and Exploitation of Microgravity” with the Cen-ter of Applied Space Technology and Microgravity(University of Bremen, Bremen, Germany), in whichhe also achieved the postdoctoral lecture qualifica-tion (1993). Then, he became the Head of Prede-

velopment in industry (1992–1996) and got offered two chair professorships(1994) for thermofluid dynamics (University of Stuttgart, Stuttgart, Germany)and for fluid mechanics and process automation (Technical University Munich,Munich, Germany). In the latter, he was a Full Professor Chair (1995–2006)as well as the Head of the Information Technology Group, the Study Dean,the First Pro Dean, and the Director of the Department of Food and NutritionSciences. Since 2006, he has been a Full Professor with the Institute of FluidMechanics (LSTM), Friedrich-Alexander University of Erlangen–Nuremberg,Erlangen, Germany. His research interests in different areas include those thatare connected to particle technology, nucleation of nanoparticles in supercriticalgases, and the fluid mechanical transport of particulate drugs in the human body.He has a track record of more than 120 publications in peer-reviewed journalsand books and is the holder of more than 30 patents. He is a Member of theEditorial Board of the “Journal of Fluid Mechanics” and a Peer Reviewer inmore than ten scientific journals and cooperates with leading research groups inthe fields of fluid mechanics and critical phenomena. Twenty Ph.D. candidatesfinished their thesis under his guidance. He supervises 18 Ph.D. students and13 postdoctoral students.