IEEE DRAFT 80 : D14 JUN 99

1 Overview
2 References
3 Definitions
4 Safety in Grounding
5 Range of tolerable current
6 Tolerable body current limit
7 Accidental ground circuit
8 Criteria of tolerable voltage
9 Principal design considerations
10 Special considerations for gas-insulated substations (GIS)
11 Selection of conductors and connections
12 Soil characteristics
13 Soil structure and selection of soil model
14 Evaluation of ground resistance
15 Determination of maximum grid current
16 Design of grounding system
17 Special areas of concern
18 Notes on the construction of a grounding system
19 Field measurements of a constructed grounding system
20 Physical scale models
Annex A Bibliography (informative)
Annex B Sample calculations (informative)
Annex C Graphical and approximate analysis of current
          division (informative)
ANNEX D Simplified step and mesh equations (informative)
Annex E Equivalent uniform soil model for non-uniform
          soils (informative)
Annex F Parametric analysis of grounding systems
          (informative)
Index
Figures
3-1 Relationship between actual values of fault current
        and values of IF, If and Df for fault duration tf
4-1 Typical faulted substation with and without
        multiple return ground paths
4-2 Equipotential contours of a typical grounding grid
        with and without ground rods
6-1 Fibrillating current versus body weight for various
        animals based on a three second duration of the
        electrical shock
6-2 Body current versus time
7-1 Exposure to touch voltage
7-2 Impedance in touch voltage circuit
7-3 Touch voltage circuit
7-4 Exposure to step voltage
7-5 Step voltage circuit
7-6 Cs versus h
8-1 Basic shock situations
8-2 Typical situation of extended transferred potential
8-3 Typical metal-to-metal touch situations in GIS
8-4 Touch voltage limits for metal-to metal contact and
        a typical range of enclosure voltage to ground
10-1 Typical faults in GISt
12-1 Soil model
12-2 Effects of moisture, temperature and salt upon soil
        resistivity
13-1 Wenner four pin method
13-2 Circuit diagram for three pin or driven rod method
13-3 Sunde's graphical method
13-4 Resistivity plot of data from soil type 2, table E2
13-5 Example of Sunde's graphical method
14-1 Coefficient k1 and k2 of Schwarz's formula
14-2 Short-time current loading capability of concrete-
        encased ground electrodes
14-3 Grid with encased vertical electrodes
15-1 Fault within local substation; local neutral grounded
15-2 Fault within local substation; neutral grounded at
        remote location
15-3 Fault in substation; system grounded at local
        substation and also at other points
15-4 Typical current division for a fault on high side of
        distribution substation
15-5 Example system for computation of current division
        factor Sf
16-1 Design procedure block diagram
17-1 Typical switch shaft grounding practice
17-2 Typical braided switch shaft grounding device
        Figure 8-1 Basic shock situations
17-3 Typical braidless switch shaft grounding device
17-4 Case 1 - plot 1
17-5 Case 1 - plot 2
17-6 Case 2 - plot 1
17-7 Case 2 - plot 2
17-8 Case 3 - plot 1
17-9 Case 3 - plot 2
17-10 Case 4 - plot 1
17-11 Case 4 - plot 2
17-12 Case 5 - plot 1
17-13 Case 5 - plot 2
17-14 Fence insulating section
17-15 Transfer potential on fence
19-1 Fall-of-potential method and earth surface
        potentials for various spacings "X"
TABLES
11-1 Material constants
11-2 Material constants
11-3 Ultimate current carrying capabilities of copper
        ground cables, X/R = 40
11-4 Ultimate current carrying capabilities of copper
        ground cables, X/R = 20
11-5 Ultimate current carrying capabilities of copper
        ground cables, X/R = 10
11-6 Ultimate current carrying capabilities of copper
        ground cables, X/R - 0
12-1 Typical surface material resistivities
13-1 Range of earth resistivity
14-1 Typical grid resistances
15-1 Typical values of Df
16-1 Typical ratio of corner-to-corner mesh voltage
16-2 Index of design parameters
ANNEX FIGURES
B1 Square grid without ground rods
B2 Square grid with twenty 7.5 m ground rods
B3 Rectangular grid with thirty-eight 10 m ground
        rods
B4 L-shaped grid with twenty-four 7.5 m ground rods
B5 Equally spaced square grid with nine rods in two-
        layer soil
B6 Diagonal voltage profile for the grid of figure
        B5 in two-layer soil
B7 Unequally spaced square grid with twenty-five 9.144 m
        rods
B8 Diagonal voltage profile for an unequally spaced
        grid in figure B7
C1-22 Curve to approximate split factor Sf
C23 System and configuration data for example 1 of C3
C24 System and configuration data for example 2 of C3
F1 One mesh current density
F2 Sixteeen mesh grid current density
F3 Four mesh grid resistance
F4 Sixteen mesh grid resistance
F5 Grid resistance versus grid depth
F6 Four mesh grid touch voltage
F7 Sixteen mesh grid touch voltages
F8 Four mesh grid step voltages
F9 Sixteen mesh grid step voltages
F10 Touch voltage versus grid depth
F11 Step voltage versus grid depth
F12 Single rod current density
F13 Multiple driven rod current density
F14 Current densities in multiple driven rods in
        two-layer soil
F15 Grid current densities - rods and grid in uniform
        soil
F16 Rod current densities - rods and grid in uniform
        soil
F17 Rod and grid current density - 9 rods and grid in
        two-layer soil
F18 Rod and grid current density - 9 rods and grid in
        two-layer soil
G1 Circuit for obtaining potential distribution
G2 Measured potential distribution for various ground
        mats
G3 Measured potential distribution for various ground
        mats
G4 Measured potential distribution for various ground
        mats
G5 Measured potential distribution for various ground
        mats
G6 Measured distribution for a ground mat with various
        mesh densities
G7 Potential distribution for ground mats with fine
        meshes in portions
G8 Square grid with twenty 7.5 m rods
G9 Potential distribution in a ground mat with ramp
        (curve 1) and without ramp (curve 2)
G10 Potential distribution around a mast footing in the
        direction A-B for a mast with ramp (curve b) and
        without ramp (curve a)
E1 Ground parameters compute with two-layer soil compared
        with those computed with equivalent uniform soil
        model
E2 Resistance & apparent resistivity data for soil
        type-1 and 2 of table E1, measured with four
        pin method
F1 Touch voltages for multiple driven rods
F2 Touch voltages for grid and ground rod combination
        in two-layer soil

 

Advises on safe outdoor ac substations, both conventional or gas-insulated. Includes distribution, transmission and generating plant substations. Applies also to indoor portions of substations, or those being entirely indoors. Does not describe grounding problems specific to dc substations or the effects of lightning surges.