Aspix Validation

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IEEE 80 Aspix Validation

IEEE 80-2013 standard has several sample calculations, which serve to validate the grounding software. Annex B has five examples of calculation of grounding grids in uniform soils and one example of calculation in two-layer soil. Annex F has the results of different arrangements of grounding systems in two-layer soils, for various reflection indexes. To test the Aspix program, the Example 2 of Appendix B (page 135) and the SR9 case of Appendix F (see table F.2, page 186) have been chosen.

1. UNIFORM SOIL VALIDATION

Figure 1 shows a plan view of the grounding grid of Example 2 of Annex B. This grounding grid is a 70 m x 70 m grid with 20 vertical rods, each 7.5 m long, around the perimeter of the grid.

Figure 1. Example 2 - Annex B – Plan view

The design data are shown in Table 1. The calculated GPR for this case is 5247 V.

Table 1. Input data for Example 2 - Annex B

The grounding grid resistance is calculated as follows:

The program of EPRI TR-100622 gives a result of 2.52 for the grid resistance.

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The step voltage is calculated as follows:

The program of EPRI TR-100622 gives a result of 459.1 V for the step voltage.

The touch voltage is calculated as follows:

The program of EPRI TR-100622 gives a result of 756.2 V for the touch voltage.

Figure 2 shows the plan view of the grounding grid simulated in Aspix.

Figure 2. Example 2 - Annex B - Aspix grounding grid plan view

Table 2 shows the simulation results. Aspix gives results of 2.488 , 784.63 V and 462.56 V for the grid resistance, touch voltage, and step voltage, respectively.

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Table 2. Example 2 - Annex B - Aspix results

Table 3 shows the comparison between IEEE 80 (using equations), the EPRI TR-100622 program and Aspix results and Table 4 shows the percentage deviations.

Table 3. IEEE 80 and Aspix results comparison

IEEE 80 EPRI TR-100622 Aspix

Resistance 2,75 2,52 2,488

Touch voltage 747,4 756,2 784,63

Step voltage 548,9 459,1 462,56

Table 4. Percentage deviation of the Aspix results

Deviation IEEE 80 Deviation EPRI TR-100622

Resistance 9,5 % 1,2 %

Touch voltage 5 % 3,8 %

Step voltage 15,7 % 0,63 %

As shown, the deviations are very low except for step voltage, in which the deviation of Aspix results respect to IEEE 80 is 15.7%; however, in this case the deviation of Aspix respect to EPRI TR-100622 program is very low 0.63%, so the Aspix results are considered valid.

2. TWO-LAYER SOIL VALIDATION

Figure 3 shows a plan view of the grounding grid of SR9 case of Annex F. This grounding grid is a 20 m x 20 m grid with 9 vertical rods, each 10 m long. The asterisk symbol (*) shown in the figure indicates the point where the maximum touch voltage is obtained.

Figure 3. SR9 Case, Annex F – Plan view

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The top layer has a resistivity of 100 m and the resistivity of the lower layer depends on the reflection factor K. In this case, the touch voltages are given as a percentage of GPR. Table 5 shows the results given by the IEEE 80.

Table 5. SR9 Case, Annex F

Figure 4 shows the plan view of the grounding grid simulated in Aspix.

Figure 4. Grounding grid plan view - SR9 Case, Annex F - IEEE 80

The reflection factor k is given by the expression:

12

12

k

Where 1 and 2 are resistivity of the upper layer and lower layer respectively. Table 6 shows the cases

simulated in Aspix.

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Table 6. Case SR9 Annex F - Simulated cases

Reflection factor k Upper layer resistivity 1 Lower layer resistivity 2

0 100 m 100 m

0,5 100 m 300 m

-0,9 100 m 5,26 m

Table 7, Table 8 and Table 9 show the Aspix results for the cases simulated.

Table 7. Case SR9 Annex F - Aspix results, k = 0

Table 8. Case SR9 Annex F - Aspix results, k = 0,5

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Table 9. Case SR9 Annex F - Aspix results, k = -0,9

Table 10 shows the comparison between IEEE 80 and Aspix results and Table 11 shows the percentage deviations.

Table 10. IEEE 80 and Aspix results comparison

k = 0 k = 0,5 k = -0,9

IEEE 80 Aspix IEEE 80 Aspix IEEE 80 Aspix

Resistance 1,81 1,768 3,5 3,48 0,164 0,162

Touch voltage 21% 21,18% 13,4% 13,69% 35% 37%

Table 11. Percentage deviation of the Aspix results

k = 0 k = 0,5 k = -0,9

Resistance 2,3% 0,6% 1,2%

Touch voltage 0.9% 2,2% 5,4%

As shown, the deviations are always less than 6%, so the Aspix results are considered valid.