AS SOON as a liquid comes into contact with a solid,

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1 IEEE TRANSACTIONS ON INDUSTRY APPLICATIONS, VOL. 45, NO. 2, MARCH/APRIL Electrical Double Layer s Development Analysis: Application to Flow Electrification in Power Transformers Juan Martin Cabaleiro, Thierry Paillat, Olivier Moreau, and Gérard Touchard, Member, IEEE Abstract A charge zone known as the electrical double layer exists at a solid liquid interface. The liquid flow induces a phenomenon called flow electrification: it generates a streaming current (caused by charge convection) and a rise in the solid s potential (if it is insulated from the ground). These potentials may reach values high enough to produce electrical discharges and cause accidents. Although this phenomenon was identified a long time ago, its physical description remains unknown (i.e., production and displacement of charges, equilibrium, etc.). We have modeled flow electrification phenomena occurring when transformer oil flows through a rectangular pressboard duct. The results of a parametric study made with this model are presented in this paper. The duct s geometry and the materials were selected to compare some of the numerical results to experimental ones. The facility used to obtain these experimental results was developed some years ago as a part of the research program of Electricité de France and the University of Poitiers. Another facility will be designed in the near future with the aim of reproducing surface electrical discharges. The results of this parametric study will be useful for its design. Index Terms Electrical double layer (EDL), flow electrification, power transformers. NOMENCLATURE As a general remark, the subscript + indicates that the respective quantity is dimensionless. a Duct s half height (in meters). D Duct s width (in meters). D 0 Liquid s mean diffusion coefficient (in meters per second). D x Displacement field in the x-direction (in coulombs per square meter). E x Electric field in the x-direction (in volts per meter). i l Linear leakage current density (in amperes per meter). Paper MSDAD-07-75, presented at the 2006 ESA/IEEE/IEJ/SFE Joint Conference on Electrostatics, Berkeley, CA, June 20 23, and approved for publication in the IEEE TRANSACTIONS ON INDUSTRY APPLICATIONS by the Electrostatic Processes Committee of the IEEE Industry Applications Society. Manuscript submitted for review October 1, 2006 and released for publication May 29, Current version published March 18, This work was supported in part by the Poitou Charentes region and in part by the University of Poitiers. J. M. Cabaleiro, T. Paillat, and G. Touchard are with the Laboratoire d Etudes Aérodynamiques, Unite Mixte de Recherche 6609, Centre National de la Recherche Scientifique, Groupe Electrofluidodynamique, Université de Poitiers, Poitiers, France ( jmcabaleiro@gmail.com). O. Moreau is with the Electrical Equipment Department, Research and Development Division, Electricité de France, Clamart, France. Digital Object Identifier /TIA i w Wall surface current density (in amperes per square meter). I acc Accumulation current (in amperes). I down Downstream leakage current (in amperes). I s Streaming current (in amperes). I up Upstream leakage current (in amperes). Kf, Kr Adsorption and desorption rates (in meters per second and units per second, respectively). L Duct s length (in meters). R surf Surface resistivity (in ohms per square meter). U Velocity (in meters per second). U m Mean velocity (in meters per second). V s Potential at the interface (in volts). w p Pressboard s thickness (in meters). w T PTFE s thickness (in meters). δ 0 Diffuse layer s thickness (also called the Debye length) (in meters). ε Liquid s dielectric constant (in farads per meter). ε p Pressboard s dielectric constant (in farads per meter). ε T PTFE s dielectric constant (in farads per meter). ρ Space charge density in the liquid (in coulombs per cubic meter). ρ w Space charge density near the wall (in coulombs per cubic meter). ρ wd Space charge density near the wall for a fully developed double layer (in coulombs per cubic meter). σ 0 Bulk liquid s conductivity (in siemens per meter). σ s Surface charge density (in coulombs per square meter). σ sd Surface charge density for a fully developed double layer (in coulombs per square meter). I. INTRODUCTION AS SOON as a liquid comes into contact with a solid, the solid liquid couple that was initially neutral becomes polarized under physicochemical reactions occurring at the interface. Such a phenomenon leads to a space charge in the liquid, and to a space charge in the solid that can accumulate according to leakage paths [1] [4]. The space charge distribution in the liquid is called an electrical double layer (EDL). Liquid convection creates a current called streaming current and leads to a continuous charge separation process at the interface. When the solid is insulated from ground, leakage impedances limit the accumulation of these charges /$ IEEE

2 598 IEEE TRANSACTIONS ON INDUSTRY APPLICATIONS, VOL. 45, NO. 2, MARCH/APRIL 2009 Fig. 2. Typical experimental results: temporal evolution of the measured currents. Fig. 3. Rectangular duct and associated coordinate system. Fig. 1. Sensor s diagram, measured currents, and equivalent electrical diagram. In our case, the liquid studied is transformer oil, and the solid is a rectangular pressboard duct, which is inserted in a polytetrafluoroethylene (PTFE) frame. This choice of materials and geometry is not arbitrary. In fact, a facility designed to study oil pressboard flow electrification phenomena was developed some years ago as a part of the research program of Electricité de France and the University of Poitiers. A complete description of this facility can be found in [3] and [4]. Basically, it consists of a sensor inserted in a forced convection loop, where several parameters like oil temperature, pressure, or flow rate can be controlled. In this sensor (Fig. 1), charge leakage takes place toward two stainless-steel couplings placed at both extremities of the duct and insulated from the rest of the loop by PTFE flange couplings. Two plane electrodes are placed facing the external surfaces of the pressboard duct, beyond 2 mm of PTFE, to measure a mainly capacitive current (I acc ) related to the charge trapped inside the pressboard (accumulation charges). Upstream and downstream leakage currents I up and I down, as well as the accumulation current, are measured by means of three picoammeters Keithley 610C. The acquisition frequency was 5 Hz. Typical experimental curves obtained are shown in Fig. 2. In this particular case, the mean flow velocity was 0.4 m/s, and flow was laminar (as in most of our experiments in this facility). Oil temperature was 20 C, and hydrostatic pressure was 0.2 bar (relative). In this paper, we model the processes taking place in the facility, and we present the results of a parametric study. II. MODEL The charge separation mechanism and the temporal evolution of space charge in the liquid are associated to current generators. At any time, their sum is equal to the sum of the accumulation current and both leakage currents (Fig. 1). The π-cell network of lumped resistances and capacitors (Fig. 1) represents the solid (pressboard PTFE) and the solid liquid interface. Equations and hypotheses used in this model are presented hereafter. Let us consider a rectangular duct of length L, whose height 2a is negligible relative to its width D (Fig. 3). Thus, the assumption of two infinite parallel plates is possible. The charge separation process at the interface has been modeled in the literature by preferential adsorption [5] and by redox-type chemical reactions [6]. In this paper, we have chosen to use a model that combines both. We will consider that a process of adsorption/desorption of ions takes place at the interface, followed by a redox reaction and, finally, a possible desorption of its products into the liquid [7]. In addition, we consider that our problem may be included among those of weak space charge density. Consequently, the liquid s conductivity near the walls does not show great

3 CABALEIRO et al.: EDL s DEVELOPMENT ANALYSIS: FLOW ELECTRIFICATION IN POWER TRANSFORMERS 599 variations. Even if this hypothesis is usually not verified close to the interface, it has been shown that the error made is only a few percent [8], which is the same order of magnitude than the experiment s accuracy. As a result, wall current density may be expressed as [7] i w (z,t) =Kf [ζ ρ w (z,t)] + Kr σ s (z,t) (1) ζ = ρ wd Kr Kf σ sd (2) where Kf and Kr are the ions adsorption and desorption rates (in this paper, we consider that they remain constant). ρ w is the space charge density near the interface, ρ wd is the space charge density near the interface for a fully developed double layer, σ s is the surface charge density, and σ sd is the surface charge density for a fully developed double layer. We assume that the time needed for the charges to distribute in the x-direction (to form the diffuse layer profile) is much shorter than the time required for the development of space charge at the interface and also shorter than the residence time of a fluid particle in the duct during the convection. With these hypotheses, the space charge density in the liquid is given by [9] ρ(x, z, t) =ρ w (z,t) cosh(x/δ 0) cosh(a/δ 0 ), δ 0 = ε.d0 σ 0 (3) with δ 0 being the diffuse layer thickness (also called the Debye length): ε is the liquid s dielectric constant, σ 0 is its bulk conductivity, and D 0 is a mean diffusion coefficient. The velocity profile for the laminar oil flow is U(x) = 3 ) 2 U m (1 x2 (4) with U m being the mean flow velocity. The streaming current due to charge convection is I s (z,t) = D/2 a D/2 a a 2 ρ(x, z, t)u(x)dxdy. (5) Charge conservation in the liquid, considering axial current occurs only due to convection, leads to 1 I s (z,t) a ρ(x, z, t) 2i w (z,t) = dx. (6) D z a After replacing i w, ρ, and I s according to (1), (3), and (5) and integrating, (6) becomes C 1 ρ w (z,t) z ρ w (z,t) +C 2 =Kf[ζ ρ w (z,t)]+kr σ s (z,t) (7) where C 1 (in square meters per second) and C 2 (in meters) are constants given by C 2 = δ 0 tanh (a/δ 0 ) C 1 =3(δ 0 /a) 2 U m [a C 2 ]. (8) Leakage currents are considered to occur at the interface according to Ohm s law, i.e., i l (z,t) = 1 V s (z,t). (9) R surf z Here, i l is a linear leakage current density, R surf is the surface resistivity, and V s is the surface potential (at the interface). Charge conservation at the interface, neglecting the conduction current toward the pressboard PTFE couple, gives i w (z,t)+ i l(z,t) z + σ s(z,t) =0. (10) Assuming a quasi-static behavior of charges, with Gauss s law, one can obtain E x (a, z, t) = C a 2 ε ρ w(z,t)+ 0 2 V (x, z, t) z 2 dx. (11) Then, we continue to apply this law starting from the liquid just above the interface toward the outer PTFE s surface (ground). Assuming that there is no space charge neither in the pressboard nor in the PTFE, and that there is no surface charge between them, we find D x (z,t) =σ s (z,t)+e x (a, z, t) (12) where D x is the displacement field in the x-direction. Finally, we can integrate D x from the ground (taking into account both mediums dielectric constants) to obtain the following surface potential (at the interface): V s (z,t) =[εe x (a, z, t)+σ s (z,t)] C 3 = 1 C 3 ε T ε p ε T w p + ε p w T (13) where ε T and ε p are the PTFE and pressboard dielectric constants, and w T and w p are their thicknesses. C 3 represents the capacitance per unit surface. E x (a, z, t) is the component of the electric field normal to the interface. From geometrical considerations, we can assume that the second term in the righthand side of (11) is negligible with respect to the first one, and thus, we have σ s (z,t) =C 3 V s (z,t) C 2 ρ w (z,t). (14) Equations (1), (7), (9), (10), and (14) can be discretized to obtain the system of equations represented by the electrical diagram shown in Fig. 1. Furthermore, these equations can be condensed in a system of two coupled partial differential equations (PDEs) as ρ + C w (z,t) 2 = Kf [ζ ρ w (z,t)] + Kr [C 3 V s (z,t) C 2 ρ w (z,t)] ρ C w (z,t) 1 z ρ C w (z,t) 1 z 1 2 V s (z,t) R surf z 2 =0. + C 3 V s (z,t) (15) This system has to be solved to obtain ρ w and V s. A finitedifference code was developed in Scilab. Different numerical

4 600 IEEE TRANSACTIONS ON INDUSTRY APPLICATIONS, VOL. 45, NO. 2, MARCH/APRIL 2009 schemes were tested. Results presented hereafter were obtained with a first-order upwind difference scheme in space and the three-time-level method in time. This numerical scheme suited our problem the best from a numerical point of view. The variables in this code are the number of nodes n, which indicates the spatial discretization degree, and the time pass dt, which indicates the temporal discretization degree. The oil parameters (σ 0 and ε were measured, and D 0 was estimated) and the mean flow velocity needed to be introduced as well. The wall current density coefficients Kf and Kr and the parameter ρ wd were obtained by fitting the model and experimental results. Discretization error was estimated for this grid to be lower than 10%. Using a finer grid would have given smaller errors, but computational time becomes very long. The simulation always starts with a static fully developed EDL. As a result, at the beginning, ρ w is equal to ρ wd and the surface potential V s is null, all along the duct. Then, laminar flow is imposed, and at a determinate time, flow can be stopped to simulate the discharge. A positive peak is observed on the experimental downstream leakage current (Fig. 2) at the beginning of the flow. It is related to an influence of the streaming current development over the downstream leakage current measurement: positive charges, convected by the flow, are detected by the downstream stainless-steel coupling, connected to the downstream picoammeter. This is an experimental issue and, therefore, has not been modeled in this paper. TABLE I SIMULATION PARAMETERS III. RESULTS All results presented from this point on are numerical results. First, we present a series of results in dimensional form, to be compared with experimental ones. These calculations helped us find the order of magnitude of some unknown parameters like adsorption/desorption rates. Then, we performed a parametric study in a dimensionless form (in order to generalize the results). Fig. 4. Simulated currents: upstream and downstream leakage currents, accumulation current, and streaming current. Surface resistivity is supposed to be constant. A. Dimensional Results With the parameters presented in Table I, we obtained the numerical results shown in Figs In Fig. 4, we present the leakage currents, accumulation current, and streaming current (I up, I down, I acc, and I streaming ). These currents were compared to experimental ones: the model reproduces the experimental results qualitatively well. Fig. 5 shows the evolution of space charge at the interface; at t =0s, we observe a constant value along the duct, but as time passes, the space charge evolves to the dynamic equilibrium distribution. We can see in Fig. 6 that surface potential evolves toward an almost symmetrical distribution with respect to the center of the duct. B. Nondimensional Results: A Parametric Study A parametric study was made to understand the influence of each parameter on the model. Fig. 5. Temporal evolution of the spatial distribution of the space charge at the interface (ρ w). In order to generalize these results, we rendered the system (15) of PDEs nondimensional. Choosing the following reference quantities: 1) conductivity (σ 0 ); 2) dielectric constant (ε);

5 CABALEIRO et al.: EDL s DEVELOPMENT ANALYSIS: FLOW ELECTRIFICATION IN POWER TRANSFORMERS 601 Fig. 6. Surface potential (V s) development. Fig. 7. Dimensionless streaming current as a function of dimensionless time for different duct heights. 3) mean diffusion coefficient (D 0 ); 4) space charge at the wall for a fully developed double layer (ρ wd ) and using the Buckingham π theorem, the system (15) becomes 3U m+ a 2 + [a + tanh(a + )] ρ w+ z + + tanh(a + ) ρ w+ ] + = Kf + [1 + tanh(a + ) Kr + Kf + ρ w+ +Kr + [C 3+ V s+ tanh(a + )ρ w+ ] 3U m+ a 2 + [a + tanh(a + )] ρ w+ z + 1 =0 where z + t + 2 V s+ R surf+ z+ 2 +C 3+ V s+ + (16) =(z/δ 0 ) dimensionless axial coordinate; =(t/τ r )=t(σ 0 /ε) dimensionless time (τ r is the diffuse layer s relaxation time); ρ w+ =(ρ w /ρ wd ) dimensionless space charge at the wall; V s+ = V s (σ 0 /(D 0 ρ wd )) dimensionless surface potential; a + U m+ Kf + Kr + R surf+ C 3+ =(a/δ 0 ) dimensionless duct s half height; = U m (τ r /δ 0 ) dimensionless mean velocity; = Kf(τ r /δ 0 ) dimensionless adsorption rate; = Krτ r dimensionless desorption rate; = R surf σ 0 δ 0 dimensionless surface resistivity; = C 3 (δ 0 /ε) dimensionless capacitance per unit surface. The dimensionless space charge and surface potential are the system s unknowns. The dimensionless axial coordinate and time are the problem variables. Finally, the last six parameters in the list above are the ones that govern the problem. We present hereafter the results of this parametric study. In a no desorption scenario (i.e., Kr =0), the PDEs of (15) are decoupled so that any variation in surface potential would have no effect on wall space charge. In order to have a more complete vision of the problem, we decided to use significant Kr coefficient for this parametric study. Even though the streaming current is not one of the system s unknowns, it is measured in almost every experiment. Therefore, we have Fig. 8. Space charge at the interface as a function of position for different duct heights at t + =0.5. included its simulated value among the results. Of course, we present its dimensionless value as I s+ = I s δ 0 D 0 ρ wd. 1) Influence of the Duct s Height: In Fig. 7, we present the streaming current s temporal evolution for four ducts of different heights. As a first observation, we can say that for a given mean velocity, streaming current will be smaller the bigger the duct s height is. Observing Fig. 8, one can see that for a given mean flow velocity, a duct with a bigger interplate distance will allow a more important development of the double layer. This occurs because the velocity near the wall is smaller, and therefore, the contact time increases. Fig. 9 shows the surface potential distribution for the four duct heights. At electric equilibrium, surface potential s peak is practically proportional to the streaming (available) current. Consequently, surface potential s peak is smaller (in absolute value) the bigger the duct s height is. Another observation might be that the dynamics of the streaming current are slower, and so is the development of surface potential. 2) Influence of Mean Flow Velocity: Fig. 10 shows that the streaming current s peak value increases almost proportionally

6 602 IEEE TRANSACTIONS ON INDUSTRY APPLICATIONS, VOL. 45, NO. 2, MARCH/APRIL 2009 Fig. 9. Surface potential as a function of position for different duct heights at t + =0.5. Fig. 12. Surface potential as a function of position for different flow velocities at t + =0.5. Fig. 10. Streaming current as a function of time for different mean flow velocities. Fig. 13. Space charge at the interface as a function of position for different Kf coefficients at t + =0.5. Fig. 14. Streaming current as a function of time for different Kf coefficients. Fig. 11. Space charge at the interface as a function of position for different flow velocities at t + =0.5. with velocity, but the dynamic equilibrium value reached increases less and less. At the beginning (flow start), the EDL is considered to be fully developed, and therefore, the convection of the charges gives a current almost proportional to mean velocity. However, an increase in velocity will produce a less developed double layer (Fig. 11), and therefore, the increase in stationary streaming current will be less important. This behavior is typical for a non-fully developed double layer. Surface potential distribution is presented in Fig. 12, and we can observe that the increase in its extremum is less and less important. 3) Influence of the Kf Coefficient: A bigger Kf coefficient will produce a greater wall current i w and, thus, a more developed double layer (Fig. 13) and a greater stationary streaming current (Fig. 14). Accordingly, the surface potential will increase. 4) Influence of the Kr Coefficient: An increase in the value of the Kr coefficient has a complex effect on the EDL. Big Kr coefficients mean high desorption and, therefore, less

7 CABALEIRO et al.: EDL s DEVELOPMENT ANALYSIS: FLOW ELECTRIFICATION IN POWER TRANSFORMERS 603 Fig. 15. Surface potential as a function of position for different Kr coefficients at t + =0.5. Fig. 17. Streaming current as a function of time for different Kr coefficients. L =0.3m. Fig. 18. Surface potential as a function of position for different surface resistivities at t + =0.5. Fig. 16. Space charge at the interface as a function of position for different Kr coefficients at t + =0.5. accumulation (lower surface potentials: Fig. 15). In addition to that, they generate flatter surface potentials and wall space charge distributions. At the entry and exit of the duct, there is a pronounced wall space charge increase (Fig. 16). In those regions, the surface potential becomes very low [V s (z =0,L)= 0] and so does desorption. An increase in wall space charge compensates in part this effect; nevertheless, wall current increases in both regions. As a result, bigger streaming currents are produced (Fig. 17). 5) Influence of the Surface Resistivity: As it was stated earlier in this paper, in a no desorption scenario, any variation in surface resistivity would have no effect on wall space charge nor on the streaming current. An increase in surface resistivity would only increase the electric time constant and the surface potential reached at equilibrium. If the desorption rate coefficient is significant, an increase in surface potential due to higher surface resistivities (Fig. 18) produces higher desorption. In this case, this causes lower wall space charges (Fig. 19) and streaming currents (Fig. 20). 6) Influence of the Capacitance Per Unit Surface: Variations in the capacitance per unit surface (C 3+ ) can be presented in the same way. In the no desorption case, an increased capacitance produces quite the same surface potential at electric Fig. 19. Space charge at the interface as a function of position for different surface resistivities at t + =0.5. equilibrium. The surface charge density σ s, however, will be more important. In the plots presented hereafter, the desorption coefficient is significant. In that case, an increased surface charge density (due to higher capacitances) produces higher desorption. As a result, we obtain lower wall space charge distributions (Fig. 21) and lower streaming currents (Fig. 22). The surface potential distribution at equilibrium will be a bit smaller due to lower streaming currents, but it will take longer to reach that equilibrium (Fig. 23).

8 604 IEEE TRANSACTIONS ON INDUSTRY APPLICATIONS, VOL. 45, NO. 2, MARCH/APRIL 2009 Fig. 20. Streaming current as a function of time for different surface resistivities. Fig. 23. Surface potential as a function of position for different capacitances per unit surface at t + =0.5. very short compared to the interfacial reactions time constants and to the residence time of a particle due to convection. The second one concerns the adsorption and desorption rates. They were considered to remain constant and to be independent of mean flow velocity for instance. The results of a parametric study have been presented and discussed: they show typical behavior of flow electrification produced by a non-fully developed EDL. These results will help us on the choice of materials and geometrical aspects of a facility that is being designed in our laboratory, in which we intend to reproduce surface electrical discharges observed in power transformers. Fig. 21. Space charge at the interface as a function of position for different capacitances per unit surface at t + =0.5. Fig. 22. Streaming current as a function of time for different capacitances per unit surface. IV. DISCUSSION We have presented a model for flow electrification phenomena produced by oil flowing in a pressboard rectangular duct. This model allows us to study the EDL development including the transient state. It reproduces fairly well the experimental data; however, two strong hypotheses need to be confirmed. The first one concerns the formation time of the EDL profile in the direction normal to the walls. This time was considered to be REFERENCES [1] J. C. Gibbings and G. S. Saluja, Electrostatic streaming current and potential in a liquid flowing through insulating pipes, Dechema. Monog., vol. 72, pp , [2] H. L. Walmsley, The electrostatic fields and potentials generated by the flow of liquid through plastic pipes, J. Electrostat., vol. 38, no. 3, pp , Nov [3] O. Moreau, T. Paillat, and G. Touchard, Flow electrification in transformers: Sensor prototype for electrostatic hazard, Electrostatics, pp , Mar [4] T. Paillat, O. Moreau, J. M. Cabaleiro, F. Perisse, and G. Touchard, Electrisation par écoulement: Modélisation electrique, J. Electrostat. Special Issue SFE, vol. 64, no. 7 9, pp , Jul [5] H. Walmsley and G. Woodford, The generation of electric currents by laminar flow of dielectric liquids, J. Phys. D, Appl. Phys., vol.14,no.10, pp , Oct [6] G. Touchard, T. W. Patzek, and C. J. Radke, A physicochemical explanation for flow electrification in low-conductivity liquids in contact with a corroding wall, IEEE Trans. Ind. Appl., vol. 32, no. 5, pp , Sep./Oct [7] A. P. Washabaugh and M. Zhan, A chemical reaction-based boundary condition for flow electrification, IEEE Trans. Dielectr. Electr. Insul., vol. 4, no. 6, pp , Dec [8] G. Touchard, H. Romat, P. O. Grimaud, and S. Watanabe, Solutions for the electrical interfacial problem between a dielectric liquid and a metallic wall: Applications to industry, in Proc. 4th Int. Conf. Properties Appl. Dielectric Mater., Jul. 1994, pp [9] G. Touchard and P. Dumargue, Transport de charges electriques par convection d un liquide dielectrique dans une conduite cylindrique metallique: La couche diffuse dans une conduite circulaire et entre deux plans paralleles, Electrichim. Acta, vol. 20, pp , [10] G. Touchard, Flow electrification of liquids, J. Electrostat., vol. 51/52, pp , May [11] E. Moreau, T. Paillat, and G. Touchard, Space charge density in dielectric and conductive liquids flowing through a glass pipe, J. Electrostat., vol. 51/52, pp , May 2001.

9 CABALEIRO et al.: EDL s DEVELOPMENT ANALYSIS: FLOW ELECTRIFICATION IN POWER TRANSFORMERS 605 Juan Martin Cabaleiro was born in He received the Mechanical Engineering degree from the University of Buenos Aires, Buenos Aires, Argentina, in 2004, and the Ph.D. degree from the Université de Poitiers, Poitiers, France, in He is currently with the Laboratoire d Etudes Aérodynamiques, Unite Mixte de Recherche 6609, Centre National de la Recherche Scientifique, Groupe Electrofluidodynamique, Université de Poitiers, Poitiers. His research interests include electrostatic hazards and liquid flow control by electrohydrodynamic actuators. Olivier Moreau was born in Nantes, France, on June 2, He received the Diploma in electrical engineering from the Polytechnic Institute of Grenoble (INPG), Grenoble, France, in In 1992, he joined the Electrical Equipment Department, Research and Development Division, Electricité de France, Clamart, France, as a Research Engineer, mainly involved in static electrification phenomena and high-frequency modeling in power transformers. He is the author of about 20 published conference proceedings and journal papers. Mr. Moreau is a member of the Society of Electrical and Electronics Engineers (SEE) of France. the electric double layer. Thierry Paillat was born in He received the B.S. degree in physics and electrical engineering and the Ph.D. degree from the Université de Poitiers, Poitiers, France, in Since 1998, he has been an Assistant Professor with the Laboratoire d Etudes Aérodynamiques, Unite Mixte de Recherche 6609, Centre National de la Recherche Scientifique, Groupe Electrofluidodynamique, Université de Poitiers. His research interests include electrostatic hazards by flow electrification of fluids and the fundamental aspects of Gérard Touchard (M 93) was born in France in He received the Ph.D. degree from the Université de Poitiers, Poitiers, France, in In 1977, he established the Groupe Electrofluidodynamique at the Université de Poitiers and has remained its Head. He became a Full Professor in During , he was a Visiting Researcher at the Massachusetts Institute of Technology, Cambridge. During , he was a Visiting Professor in the Department of Chemical Engineering, University of California, Berkeley. He is the author or coauthor of more than 300 papers. His research interests include interactions between flows and electrical phenomena. Dr. Touchard is a member of the Russian Academy of Engineers. In 1997, he established the Société Française d Electrostatique and has remained its Chairman. He has organized several international conferences on electrostatics.