Ieee 80 2013 Guide For Safety In Ac Substation Grounding.pdf

IEEE Std 80-2013 IEEE Gulde for Safety In AC Substatlon Grounding

Schwarz used the following equation introduced by Sunde [B134] and Rüdenberg [B131] to combine the resistance ofthe grid, rods, and mutual ground resistance to calculate the total system resistance, Rg. (58)

where R1

R2 Rm

ground resistance ofgrid conductors inQ ground resistance ofall ground rods inQ mutual ground resistance between the group ofgrid conductors, R1, and group ofground rods, R2 inQ

Ground resistance ofthe grid (59)

where p

Le a' a' 2a A k1, k2

is the soil resistivity in íl-m is the total length ofall connected grid conductors in m is .../a x 2h for conductors buried at depth h in m, or is a for conductor on earth surface in m is the diameter ofconductor in m is the area covered by conductors in m2 are the coefficients (see Figure 24(a) and (b))

Ground resistance ofthe rod bed (60)

where L,

is the length ofeach rod in m

2b

is the diameter ofrod in m number ofrods placed in area A

nR

Mutual ground resistance between the grid and the rod bed (61)

The combined ground resistance of the grid and the rod bed will be lower than the ground resistance of either component alone, but still higher than that ofa parallel combination.

68

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IEEE Std 80-2013 IEEE Guida for Safety in AC Substation Grounding

Schwarz compared the results of his equations to previously published theoretical work and to model tests to verify the accuracy of his equations. Since they were published in 1954, Schwarz's equations have been modified by Kercel [B95] to provide equations for constants k1 and k2 and further expanded to include the use of equations in two-layer soil (Nahman and Salamon [Bl 16][Bl 17]). 1.40 1.35 1.30 § 1.25

"E a,

1

o

ü

1.20

1.15 1.10

1.05 1.00

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',,"

'

"-... .....

.........

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0.95 0.90 0.85

2

4

3

5

6

7

8

LENGTH-TO-WIDTH RATIO CURVE A - FOR DEPTH h = O YA = -0.04x+1.41 CURVE B- FOR DEPTH h = 1/10 JAREA Ye = -0.05x + 1.20 CURVE C- FOR DEPTH h = 1/6 JAREA = -0.05x+ .13 1 Ye 7.0

-

·¡:;

6.5 6.0 5.5 5.0 4.5 4.0

�

-�

-

i..---

�

ec

3.5 6 5 4 2 3 LENGTH-TO-WIDTH RATIO

7

8

CURVE A - FOR DEPTH h = O YA = 0.15x + 5.50 CURVE B- FOR DEPTH h = 1/10 JAREA Ye = 0.10x + 4.68 CURVE C - FOR DEPTH h = 1/6 AREA = -0.05x + 4.40 Ye

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Figure 24-Coefficients k1 and k2 of Schwarz's formula: (a) coefficient k1, (b) coefficient k2 69

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IEEE Std 80-2013 IEEE Guide for Safety in AC Substation Grounding

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r-

------+---------- r; c 1

1

◄

=0

Figure 27 -Fault within local substation; local neutral grounded

Figure 28-Fault within local substation; neutral grounded at remote location

-1F 2

GROUNOEO STA1100 STRUCTURE

-1F OlHER SYSTEII GROUNOS

2

Figure 29-Fault In substation; system grounded at local substation and also at other polnts

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