Etep calculation

[kanjanathep]

I have been calculation ground grid system by ETEP 4.0.0 version Given:Area 90*68mm^2
surface material is crushed rock;10 cm
top layer 100 ohm/m
low layer 20ohm/m
fault current 31.5 kA,X=6
fault duration time 1 sec
grid current factor 100%
conductor is commercial Hard-Drawn
Rods are copper-clad steel rods...
So...I want to know total of rods,and grund grid....what are other factor should we consider...

thank you

jack

 

[jghrist]

See IEEE Std 80-2000, IEEE guide for safety in AC substation grounding.

Abstract
Outdoor ac substations, either conventional or gas-insulated, are covered in this guide. Distribution, transmission, and generating plant substations are also included. With proper caution, the methods described herein are also applicable to indoor portions of such substations, or to sub-stations that are wholly indoors. No attempt is made to cover the grounding problems peculiar to dc substations. A quantitative analysis of the effects of lightning surges is also beyond the scope of this guide.

 

[7anoter4]

See also [if Power Generation Station is involved only!]:
IEEE Std-665-1995[(reaffirmed 2001)
IEEE STANDARD FOR GENERATING STATION GROUNDING
CONTENTS
1-OVERVIEW
2-REFERENCES
3-DEFINITIONS
4-DESIGN OBJECTIVES
4.1-NEUTRAL GROUND,EQUIP.GRND.AND SAFETY GROUND
4.2-STATION GROUNDING SYSTEM
4.3-PREVENTING THE TRANSFER OF HIGH GROUND VOLTAGES
4.4-DESIGN OBJECTIVES
5-DETAILED DESIGN CONSIDERATIONS
5.1-GROUNDING PRINCIPLES
5.2-GROUNDING GRID DESIGN
5.3-GENERATOR AND ISOLATED PHASE BUS GROUNDING
5.4-GROUNDING OF BUILDINGS,FENCES,AND STRUCTURES
5.5-GROUNDING OF GENERATING STATION AUXILIARIES
5.6-LIGHTNING PROTECTION FOR GENERATING STATION STRUCTURES
5.7-GROUNDING OF BURIED STRUCTURES
5.8-SIZING OF GROUNDING CONDUCTORS
6-BIBLIOGRAPHY
ANNEXES
A-K FACTOR
B-CORROSION
C-DIVISION OF CURRENT FOR SMALL INTERIOR GRIDS
C.1-PURPOSE
C.2-CALCULATION
C.3-SUMMARY OF RESULTS

 

[7anoter4]

Calculated according to IEEE 80/2000 [as jghrist indicated] :
The Vrise [Potential Rise] will be still elevated [3.5 kV]
But you can reduce the Touch and Step Potential as required for 50 Kg body.
The Grid then would be:
1)Bare stranded copper 120 sqr.mm[250 MCM] total length 3.116 km[approx. 10000 ft]
The distance between parallel cables 4m[13.4 ft]*3.8 m[12.4 ft]
2) 120 vertical rods of 15 m length[50 ft] of 3/4"diameter[17 mm]
Touch Potential 1125 V admissible[crushed rock resistance 2000 ohm.m] actually = 99.5%
Step Potential 4152 V admissible and actually will be 21%
Rmat =0.109 ohm
Regards