baltoche

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Posts posted by baltoche


Gents,
Thanks for your contributions. By fall of potential method, I meant this using 3 électrodes:
 E, which is the electrode to be measured
 P, which is the potential electrode
 C, the current electrode
The testing current is impressed in E and returns through C. See attached for illustration.
Regards.
0 
Dear All,
Suppose I have two parallel conductors of different lengths in a homogeneous soil of resistivity Rho, and separated by a height of H. Is there any existing formula to calculate the mutual resistance (in DC) between them ?
With my thanks.
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Dear All,
I’d like to share an experience with the fall of potential method: if I call E the electrode under measurement (in a square arrangement of approx. 20m), P the inner Potential electrode and C the outer current electrode, I could get a flat curve of the E resistance whilst C was away from E by a distance corresponding roughly to the side of E. I was quite surprised since I thought this distance was too short and I expected a non flat resistance curve since E and C were supposed to couple with each other. Hence a question: can you theoretically get a flat curve when E and C voltage gradients still significantly overlap and, if so, does it necessarily mean that the resistance corresponding to the middle of this curve correspond to the real resistance of E to earth ?
Thanks for your lights.
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Dear All,
Thank you for your respective contributions. I do appreciate ! the reason why I need this function is because I need to integrate it in function of x.
Have your codes been typed on Matlab ? Do I need module "Symbolic Math Toolbox" to try your code ?
Thanks again and Regards,
Cédric
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Dear All,
I'm trying to find function J(x) shown in attached file. Could somebody help me ? It seems that I don't have the right tool to solve it
Thanks and Regards.
0 
Well caught, thank you very much for your support from the beginning. I'll not be involved myself into finite elements, but an engineering student will dot it for me. I've got a licence of CST, do you know this tool ?
One last question please : have you got any opinion on the resistor value of my cube edges ?
Kind Regards.
0 
Do you know if Comsol also deals with electrical fields ? Is it a freeware software ?
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Oh I see, thanks !
Do you personally use these tools, and especially the circuit simulation one ?
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I'll try this, thanks. But is OctaveForge somehow related to Matlab or not ?
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Thanks for your reply. Is there any special module to access to this functionality ? I have the basic licence only.
Regards.
0 
Dear All,
Suppose I've got a medium (like a soil) of a homogeneous and constant resistivity Rho (in Ohm.km). This medium is put into a big cube of 1km side, then giving a km3 of my medium.
Now suppose I want to model my cube by an electrical circuit with resistors at each side of the cube. May I state that each resistor will be Rhox4 then ?
No suppose I divide my km3 into equal 8 cubes of 500m side each and suppose I still want to model this arrangement by electrical resistors. What should be the value of each resistor/side then if I need that the whole set still corresponds to a resistivity of Rho ? I propose Rhox9/2. Am I right ?
For these who know Matlab, can Matlab simulate this kind of 3D electric circuit with cubes whose sides are resistors ? Is there any special module to perform this function ?
Thanks to All.
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Dear All,
Does somewhat know this software well ? I'm trying to get potentials in the ground but below the surface of the soil, and what I only managed to get so far are potentials on the soil surface. This does not surprise me since this software is intended to calculate step and touch potential for people staying or walking ON the soil, and not for dead people buried in the ground...
If Cymegrid cannot achieve this, would CDEGS do the job ?
Thanks.
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Hello Studiot,
Please find attached a sketch, where 3 soil layers have been represented. A current is impressed in P and the goal is to determine the potential of points M1, M2 and M3 with respect to far earth.
If my purposes are not clear, please get back to me.
Kind Regards.
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Hello Studiot,
Thanks for your kind contribution. Ideally, I'm after a function of A in order to plot it, knowing that I know between what values (O and Pi) I need to integrate this function. Actually, I asked for the primitive in order to calculate the integral, which is also a function of A, and this is the one I'd like to plot.
For your information, this primitive/integral is needed too solve Bessel's equation and function.
I'm sorry for the poor quality of my English.
Kind Regards.
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I know the values between whom I need to integrate this function, but it does not solve my issue... Regarding numerical methods (calculating a rough surface for instance), I cannot do it since my final integral will be a function of A.
If the answer is not an elementary function, is there a way to approach it ?
Thanks in advance.
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Good evening,
To Studiot : As fas as electrodes are concerned, my current is impressed by several voltage sources located at different places on a conductor that is laid down the soil. Currents leak from this conductor. Therefore, there are several electrodes. I'll put a sketch later on.
To RiceAway : thanks for your contribution. My purpose is not to measure the soil resistivity, but to assume several layers (with their respective resistivity's and thicknesses) of soil and from this assumption, calculate the potential of a point P in the soil depending on its relative location with respect to the injection, and of course depending on the characteristics of the soil layers that are mentioned above. With border conditions, I've come to Bessel equation and functions, but I'm not sure it is the best way to proceed...
Regards.
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Dear All,
I'm trying to find a primitive of f(x)=cos(Asin(x)) where A is a constant number.
I've tried Wolfram but unsuccessfully. An approximate function of this primitive would also be welcome.
Thanks for your help !
Kind Regards.
0 
Dear All,
I would enjoy your help on electrical geophysics .
Suppose a soil divided into 3 layers, each of them having a different electrical resistivity (Rho1, Rho2 and Rho3, starting from the top to the bottom)
Now suppose a dc current injection from a point M located at the top surface of the soil. This injection is vertical, going from the top (surface of the soil) to the bottom. My purpose is to assess the electrical potential (with respect to far earth) of a point P (coordinates : x, y and z with respect to point M) depending on the injected dc current, the coordinates of P, and the 3 soil resistivities.
I've come to Bessel equations and functions, but there may be a more simple way to proceed.
Any light on my concern please ?
Thanks and Regards.
0 
I indeed assumed that a grid consisted of a loop (with intermediate crossbonds) of round copper or steel buried in the ground and occupying a given surface (Lxl). During an MV fault, part of the fault current will be dissipated in the ground through this grid (called A). At the same time, another part of the fault current will dissipate in the same ground through another nearby grid (called B). I guess that my influence zone related to grid A depends on the fault current dissipated through A besides the geometry of the grid itself. Same case for grid B.
Is there a way to assess the respective influence zones of grids A and B from a geographical point of view so as to assess the overlap between them ?
Thanks and Regards.
0 
You've perfectly understood the context of my issue. I'm just adding that there is a conductor C (like a gas or water pipe, conductor B more being a slab steel reinforcement) that also behaves as a victim. Another variation is the soil resistivity along the line, as well as the rail insulation. This makes the circuit a bit more complex, hence the need of Matlab if I divide my line into short sections.
Having said that, I read carefully your model. What do you mean by "computed resistance" please ?
The ground resistivity and the rail insulation are assumed.
With these three conductors (A, B and C), is your model still applicable ?
Good night.
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Dear electician friends,
Suppose I have got two horizontal ground grids laid at the same depth and separated by a distance "d". How to calculate "d" so that my grids are independant from each other, meaning that I can bond them together and calculate an equivalent resistance by 1/(1/R1+1/R2) ?
With my thanks !
0 
My conductor is around 10 mOhm/km and my ground could be down to 30 Ohm.m. My conductor B corresponds to steel reinforcement and may be of the order of my conductor A resistance per length.
As far as my injection is concerned, it is not intentional. This currents comes from a transverse voltage between conductors A and B, knowing that the insulation resistance between A and B is far to be perfect, thus generating a current whose part reaches my ground.
My goal by sectionalising my conductor A is to get a network of resistors, that I'd like to resolve with Matlab.
I found a paper on Internet, slightly describing the environment of my model. I attached it for you. Section 2 is the most appropriate to my concern. The authors apply EMC model to a dc model in 3D arrangement. Section 2.2 is easy to understand. However, Section 2.3 (longitudinal model) is less easy for me. Nodes seem to be bonded to each other through a resistor but I cannot seize the formula. Maybe it is a classic formula for capacitive coupling on transmission lines in parallel, who knows... I'm far to be an EMC man and this may explain my lacks... Maybe it will more ring a bell to you.
Kind Regards.
PS : I have an issue in cutting and pasting text and figures on the forum. Is there a clue to achieve this ?
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Hello Enthalpy,
You got me, I'm indeed from a French speaking country .
I also hope that nobody feels excluded. anyway, everybody is welcome to join us !
Yes, I can confirm that conductors are very long compared to their depth.
The current finally returns to conductor A, but as I divided this conductor into N sections, I've got approx. N nodes where this current can partly return. My real problem is to model my soil (both between nodes and between a given node and far earth) into a network of resistors, and to give a value to these resistors. It calls coupling notions that I don't have.
Thanks and Regards.
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To Enthalpy...
Thanks for your return. I agree with you on that the long wire A should be modelled by half a cylinder whilst B should be modelled by half a cylinder.
As a start, could we work with a common resistivity (rho). If you forget conductor C for the moment, are you able to model the ground with resistances ?
To answer your latest question, all currents leaving conductor A goes back to the negative of a rectifier somewhere
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Mutual resistance of two conductors in the ground
in Classical Physics
Posted
Dear All,
If I have two conductors in a homogeneous ground (constant resistivity), parallel to each other and of the same length. each of them has got a transverse resistance to earth. I'd like to find an electrical model to represent the mutual resistance between these two conductors. Is it possible to do this by an analytic approach (and not only by finite elements) ?
I was thinking of splitting each conductors into a given number of segments.
Thanks for your support.
Regards.