Method of Moments in Electromagnectics 1

[nhiubong2006]

Hello everybody!
Could anyone show me the Method of Moments in Electromagnectics. How to apply this method to calculate touch voltage and step voltage????
Thank in advance!

 

[waross]

Review Ohms law,
IR=E
Current flowing in the ground = I
Effective resistance of three lineal feet of ground = R
Touch voltage = E

 

[jghrist]

See:

Melipoulos, A.P.S.; Xia, F.; Joy, E.B.; Cokkinides, G.J.
"An advanced computer model for grounding system analysis"
IEEE Transactions on Power Delivery, Jan. 1993, Volume: 8 , Issue: 1, pp 13 - 23
Abstract
An advanced methodology and a computer model for analysis of practical grounding systems based on the method of moments are presented. The practical methodology is applicable to both simple and complex grounding systems. The grounding system may consist of cylindrical conductors as well as rectangular earth conductors or metallic surfaces buried in earth or located on the surface of the earth. The method consists of computing an equivalent circuit model of the earth embedded electrodes and conductive soil. Uniform or two-layer soil can he accommodated. The problem of computational efficiency is addressed. Several innovations have been introduced to minimize execution time, including adaptive segmentation of grounding structures and adaptive computation of self and mutual impedances. The procedure enables accurate computation of touch and step voltages, body currents, grounding system impedance, voltage profile, etc. The method and computer program have been validated with actual system measurements

F. P. Dawalibi and D. Mukhedkar,
"Optimum Design of Substation Grounding in Two-Layer Earth Structure - Part II, Comparison Between Theoretical and Experimental Results,"
IEEE Transactions on Power Apparatus and Systems,Vol.PAS-94, No. 2, March/April 1975, pp. 262-266.

Ma, J. and Dawalibi, F.P.
"Modern computational methods for the design and analysis of power system grounding"
1998 International Conference on Power System Technology, 1998. Proceedings. POWERCON '98,18-21 Aug. 1998, Volume: 1
pp 122 - 126
Abstract
This paper examines a few methods used in power system grounding analysis and illustrates the advantages, limitations and the applicability of these methods. Computation results using these methods are presented and compared the various cases modeled in this paper include grounding networks of different sizes, grounding networks with buried metallic structures, such as steel pipes, and high frequency cases. The discussions and conclusions given in this paper can be used as a reference when deciding which method should be used to carry out an accurate and efficient grounding analysis

 

[cuky2000]

Here is a link with current method to determine the step and touch potentials based in IEEE Std 80.
Allowable Voltages:

http://cuky2000.250free.com/GND_Touch1.jpg

Max. Grid Voltage:

http://cuky2000.250free.com/GND-Ratio_Touch_Step_V_Calc.pdf

_{COMMENT:
I am not sure if the Method of Moments in Electromagnetic was considered in IEEE Std 80 or IEC Std 479-1 for calculating the touch and step voltages. Could you please share with us the source of your question?}

 

[jghrist]

Cuky,

The method of moments was not used in the simplified IEEE Std 80-2000 Section 16.5 equations for step and mesh voltages but is the method used in the computer analysis described in Section 16.8.