CYMGRD 6.3 for Windows
Chapter 6 Comparison with the IEEE80 Guide
6.1
Comparison with the IEEE80 Guide
We have used the following four IEEE cases in order to provide a comparison with the results obtained using CYMGRD. •
Example 1: Preliminary design stage IEEE80 GUIDE, 2000 Edition, Page 129. Square grid 70m x 70m, 100 meshes with no ground rods.
•
Example 2: Improved design IEEE80 GUIDE, 2000 Edition, Page 132. Square grid 70m x 70m, 100 meshes with ground rods placed along the perimeter.
•
Example 3: Finalized design IEEE80 GUIDE, 2000 Edition, Page 137.
Rectangular grid 63m x 84m, 108 meshes with ground rods placed along the perimeter and at selected places in the gird in an effort to further minimize surface touch potentials. •
Example 4: L-Shaped Grid with Ground Rods IEEE80 GUIDE, 2000 Edition, Page 139.
CYMGRD utilizes a finite element analysis algorithm, which is more accurate than the approximate formulas provided in the IEEE80 GUIDE. The finite element analysis algorithm enables CYMGRD to analyze grounding systems of either symmetrical or asymmetrical configuration of ground conductors and rods.
6.1.1
CASE NAME
: Example 1: Preliminary design stage.
REFERENCE
: IEEE80 GUIDE, 2000 Edition, Page 129.
SOIL MODEL
: Uniform. Soil resistivity = 400 ohm-meters.
Chapter 6 – Comparison with the IEEE80 Guide
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CYMGRD 6.3 for Windows
A. SAFETY CALCULATIONS: Input data: Body weight Crushed rock surface layer resistivity Crushed rock surface layer thickness Clearing time Uniform soil resistivity Max LG fault current, X/R (Local) LG fault current (Remote) Split factor Sf Conductor material Ambient temperature
70 Kg 2500 Ω-m 0.102 m 0.50 sec 400 Ω-m 6814 A, 16.2 3180 0.6 Copper hard-drawn 40 Celsius
Results: REFERENCE
Conductor Sizing
MAX. ALLOWABLE TOUCH
MAX. STEP
ALLOWABLE
CYMGRD IEEE Guide 80
2/0 AWG 2/0 AWG
840.55 Volts 838.20 Volts
2,696.10 Volts 2,686.00 Volts
REDUCTION FACTOR CS
0.740 0.740
B. GRID DESIGN ASPECTS: Input data: Square grid, 70m x 70m, 100 meshes with no ground rods as shown in the IEEE 80 EXAMPLE 1 STATION LAYOUT figure shown below. Square grid Grid conductor diameter Burial depth Remote contribution of the LG-fault current Split factor Uniform soil resistivity
70m x 70m, 100 meshes 0.01 m 0.5 m 3180 Amps 0.6 (User defined) 400 Ω-m
Results: In the table that follows ‘Rg’ and ‘GPR’ respectively mean the station resistance and the ground potential rise.
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REFERENCE
RG
GPR
CYMGRD IEEE Guide 80
2.675 Ohms 2.780 Ohms
5,105.61 Volts 5,304.00 Volts
Chapter 6 - Comparison with the IEEE80 Guide
CYMGRD 6.3 for Windows
Please note: For Example I, the RG calculated with the EPRI TR-10062 computer program, is 2.67 Ohms (see IEEE Guide 2000, page 134).
Chapter 6 – Comparison with the IEEE80 Guide
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CYMGRD 6.3 for Windows
6.1.2
CASE NAME
: Example 2: Improved design.
REFERENCE
: IEEE80 GUIDE, 2000 Edition, Page 134.
SOIL MODEL
: Uniform. Soil resistivity = 400 ohm-meters.
A. SAFETY CALCULATIONS: Input data: Body weight Crushed rock surface layer resistivity Crushed rock surface layer thickness Clearing time Uniform Soil Resistivity
70 Kg 2500 Ω-m 0.102 m 0.50 sec 400 Ω-m
Results: REFERENCE
MAX. TOUCH
ALLOWABLE
CYMGRD IEEE Guide 80
840.55 Volts 838.20 Volts
MAX. ALLOWABLE STEP
REDUCTION FACTOR CS
2,696.10 Volts 2,686.00 Volts
0.740 0.740
B. GRID DESIGN ASPECTS: Input data: Square grid 70m x 70m, 100 meshes with ground rods placed along the perimeter as shown in the IEEE 80 EXAMPLE 2 STATION LAYOUT figure shown below. Square Grid Grid conductor diameter Length of Ground rods Ground rod diameter Burial Depth Injected ground current Uniform soil resistivity
70m x 70m, 100 meshes 0.01 m 7.50 m 0.01 m 0.5 m 1,908 Amps 400 Ω-m
Results: In the table that follows ‘Rg’ and ‘GPR’ respectively mean the station resistance and the ground potential rise.
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REFERENCE
RG
GPR
CYMGRD IEEE Guide 80
2.500 2.750
4,780.00 Volts 5,247.00 Volts
Chapter 6 - Comparison with the IEEE80 Guide
CYMGRD 6.3 for Windows
Please note: For Example II, the RG calculated with the EPRI TR-10062 computer program, is 2.52 Ohms (see IEEE Guide 2000, page 137).
Chapter 6 – Comparison with the IEEE80 Guide
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CYMGRD 6.3 for Windows
6.1.3
CASE NAME
: Example 3: Finalized design.
REFERENCE
: IEEE80 GUIDE, 2000 Edition, Page 137.
SOIL MODEL
: Uniform. Soil resistivity = 400 ohm-meters.
A. SAFETY CALCULATIONS: Input data: Body weight Crushed rock surface layer resistivity Crushed rock surface layer thickness Clearing time Uniform Soil Resistivity
70 Kg 2500 Ω-m 0.102 m 0.50 sec 400 Ω-m
Results: REFERENCE
MAX. TOUCH
ALLOWABLE
CYMGRD IEEE Guide 80
840.55 Volts 838.20 Volts
MAX. ALLOWABLE STEP
REDUCTION FACTOR CS
2,696.10 Volts 2,686.00 Volts
0.740 0.740
B. GRID DESIGN ASPECTS: Input data: Rectangular grid 63m x 84m, 108 meshes with ground rods placed along the perimeter and at selected places in the gird in an effort to further minimize surface touch potentials, as shown in the IEEE 80 EXAMPLE 3 STATION LAYOUT figure shown below. Rectangular Grid Grid conductor diameter Length of Ground rods Ground rod diameter Burial Depth Injected ground current Uniform soil resistivity
70m x 70m, 100 meshes 0.01 m 10.0 m 0.01 m 0.5 m 1,908 Amps 400 Ω-m
Results: In the table that follows ‘Rg’ and ‘GPR’ respectively mean the station resistance and the ground potential rise.
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REFERENCE
RG
GPR
CYMGRD IEEE Guide 80
2.278 Ohms 2.620 Ohms
4,348.00 Volts 4,998.96 Volts
Chapter 6 - Comparison with the IEEE80 Guide
CYMGRD 6.3 for Windows
Please note: For Example III, the RG calculated with the EPRI TR-10062 computer program, is 2.28 Ohms (see IEEE Guide 2000, page 138).
CASE NAME
: Example 4: L-Shaped with rods.
REFERENCE
: IEEE80 GUIDE, 2000 Edition, Page 139.
SOIL MODEL
: Uniform. Soil resistivity = 400 ohm-meters.
SAFETY CALCULATIONS: Same as Example 3. A. GRID DESIGN ASPECTS: L-Shaped Grid, with the same effective grounding area as before, as shown in IEEE Std 2000, page 140.
Chapter 6 – Comparison with the IEEE80 Guide
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CYMGRD 6.3 for Windows
Results: In the table that follows ‘Rg’ and ‘GPR’ respectively mean the station resistance and the ground potential rise. REFERENCE
RG
GPR
CYMGRD IEEE Guide 80
2.330 Ohms 2.740 Ohms
4,562.49 Volts 5,227.92 Volts
Please note: For Example IV, the RG calculated with the EPRI TR-10062 computer program, is 2.34 Ohms (see IEEE Guide 2000, page 142). The 12 IEEE samples study files included in the above analysis cases are available upon request. Please contact CYME International T&D and ask for the “CYMGRD Benchmark cases.”
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Chapter 6 - Comparison with the IEEE80 Guide
