The document discusses the grounding design of the Kano Hydro Power Station in Nigeria. It provides background on the authors and Skipper Electrical. It then summarizes the key aspects of designing the grounding system, including measuring soil resistivity, calculating touch and step potentials, and following relevant safety standards and codes. The results of the initial grounding design are presented, but the final design had to be re-evaluated after excavation revealed much higher soil resistivity in some areas than initially measured. The final design ensures touch and step potentials are within safe limits across the power house and switchyard.

1. Grounding Design of Kano Hydro Power
Station(1x8MW+1x2MW) in Kano State of
Nigeria
AUTHOR
 PANKAJ SACHDEVA,JOINT GROUP PRESIDENT,SKIPPER ELECTRICAL(I) LIMITED.
 M.L.SACHDEVA,FORMER CE,CEA AND SR. CONSULTANT,SKIPPER ELECTRICAL(I) LIMITED
 S.L.NARASIMHAN,FORMER EE,K.P.C,BANGALORE AND DIRECTOR(ELECTRICAL),BHEC PVT. LTD
PRESENTED BY
 SOURAV GHOSH,ENGINEER AT SKIPPER ELECTRICAL(I) LIMITED

2. ABOUT M/S SKIPPER.
 PRESENCE IN 50 COUNTRIES,MOSTLY EXPORT ORIENTD
 MANUFACTURING PLANT :
 IN INDIA -3 NOS. BHIWADI
 IN NIGERIA – 2NOS LOGAS
 IN DUBAI - 1No
 RANGE OF PRODUCT PRESNTLY UPTO 220KV SYSTEM & UPGRADING TO 400KV.
 POWER TRANSFORMER- UPTO 65MVA,220KV S/S
 CT,PT,ISOLATORS,CBs
 C&R PANELS, CAPACITOR,LT PANELS ETC.
 PACKAGED S/S AND MOBILE SUBSTATION
 PLANNING, DESIGN, ERECTION, TESTING & COMMISSIONING OF AIS and GIS
 SCADA AND COMMUNICATION
 NEW TRANSFORMER PLANT - UPTO 800KV TR.( Under Building)
 Railway Electrification

3. SYNOPSIS
THIS PAPER DEALS WITH GROUND MAT DESIGN OF POWER
HOUSE AND SWITCHYARD WITH DIFFERENT SOIL RESISTIVITY
VALUES AND DIFFERENT CALCULATED TOUCH AND STEP
POTENTIALS WHICH IN SOME CASES EXCEED THE LIMIT
VALUES
SUGGESTIONS ON REVIEWING OF PROVISIONS OF THE
GROUND MAT DESIGN OF SMALL HYDRO POWER HOUSES.

4. INTRODUCTION
 GENERATING STATIONS AND SWITCHYARDS HAVE TO BE
EFFECTIVELY EARTHED FROM SAFETY CONSIDERATION
COVERED UNDER LEGAL PROVISIONS OF ELECTRICITY
REGULATIONS, ACTS, COMMISSIONS, ETC.
 GUIDANCE PROVIDED UNDER SAFETY CODES AND STANDARDS.
 EACH COUNTRY HAS HIS OWN GOVERNING REGULATIONS AND
STANDARDS / CODES FOR GROUNDING OF ELECTRICAL
INSTALLATIONS.

5. DESIGN CONCEPT
THE DESIGN OF GROUND MAT IS TAKEN UP CONSIDERING THE
FOLLOWING:
 PLOT LAY OUT OF S/S / LAYOUT OF A POWER HOUSE(L X B )
 SOIL RESISTIVITY (OHM-M)
 SURFACE RESISTIVITY -RIVER STONE/CRUSHED STONE/WASHED
GRANITE/ CONCRETE ( OHM-M)
 MAXIMUM PERMISSIBLE GROUND RESISTANCE OF SUBSTATION
/POWER HOUSE (OHM)
 SHORT CIRCUIT CURRENT (KA) AND ITS DURATION (SEC)
 DURATION OF SHOCK (SEC)
 DEPTH OF BURIAL OF GROUND MAT MEMBER (MM)
 MATERIAL OF GROUND MAT ( STEEL/COPPER)
 STEP POTENTIAL ( VOLTS)
 TOUCH POTENTIAL ( VOLTS)

6. MEASUREMENT OF SOIL RESISTIVITY
 A TYPICAL EARTH TESTER HAS FOUR (4)
TERMINALS.C1, P1, C2, P2 AND FOUR (4) ELECTRODES
SUPPLIED WITH THE INSTRUMENT ARE DRIVEN IN THE
GROUND AT SPECIFIED EQUAL DISTANCES THRU CABLE AND
CONNECTED TO THE INSTRUMENT IN THE ORDER OF C1, P1
AND P2, C2.
 SPECIFIC RESISTIVITY =2 Π.A. R

7. WENNER METHOD FOR CALCULATING
SOIL RESISTIVITY
ρ=2ΠaR

8. Notes
(i)DEPTH OF BURIED ELECTRODES ASSUMED
NEGLIGIBLE AS COMPARED TO SPACING BETWEEN
ELECTRODES.
ii)MORE THE DISTANCE BETWEEN ELECTRODES
MORE THE DEPTH AT WHICH SOIL RESISTIVITY IS
MEASURED.
iii) IF SOIL OF HIGH RESISTIVITY IS AT TOP
SURFACE AND SOIL RESISTIVITY AT DEEP LEVEL IS
TO BE MEASURED, TWO OR MORE RESONANCE
MODEL OF SOIL RESISTIVITY MEASUREMENT IS
ADOPTED.

9. STANDARDS AND CODES
 IS: 3043(4th Reprint June 2007 including Amendment No 1/
Jan 2007 and Amendment 2 / Jan 2010): Code of Practice for
Earthing Electrical Installations.
 CBI&P Publication No 223: Design of Earthing Mat of High
Voltage Substations
 IEEE 80-2000: Guide for Safety in AC Substation Grounding
 IEEE 665-1995: Guide for Generating Station Grounding.
 BS: 7430 -1998: Code of Practice for Earthing

10. Estimation OF EARTHHING MATERIAL
 PRELIMINARY SOIL RESISTIVITY ( INITIAL ESTIMATION)
 AS THE SWITCHYARD PLANNED TO BE ERECTED FIRST, THE SOIL RESISTIVITY WAS
MEASURED OVER A LEVEL PORTION OF LAND EARMARKED FOR POWER HOUSE.
 THE SOIL RESISTIVITY MEASSUREMENT MEASUREMENT= 80 OHM-M
 EARTHING MATERIAL ( COPPER ) ESTIMATED
 PROCUREMENT ACTION INITIATED
 FINAL SOIL RESISTIVITY (FINAL MEASUREMENT & ESTIMATION)
 THE EXCAVATION OF POWER HOUSE COMPLETED AND SWITCHYARD APPROX LEVELLED
 SOIL RESISTIVITY LEVELS MEASURED AS UNDER
 MAIN POWER HOUSE ( 8MW RBU) - 670 OHM-M
 CANAL BAY UNIT ( 2MW) - 120 OHM-M
 SWITCHGEAR ROOM & SERVICE BAY - 120 OHM-M
 OUT DOOR SWITCHYARD (ODY) - 120 OHM-M


11. POWER HOUSE
 THE SITE OF POWER HOUSE IS EXCAVATED FIRST TO THE DESIRED
GRADES AND SITE IS LEVELED.
 THE GROUND MAT MEMBERS ARE LAID ON THE SURFACE OF CLEANED
ROCK IN CASE OF ROCKY SURFACE OR BORROWS MADE AT SPECIFIED
DEPTH (650MM) IN FISSURED ROCK OR HARD SOIL.
 THE GROUND MEMBERS AND RISERS (WHERE REQUIRED) ARE JOINTED
AT CROSSING POINTS BY WELDING/ BRAZING/ EXOTHERMIC MOLD.
 THE CONCRETE FLOOR IS LAID DOWN. THE END MEMBERS (X AND Y
AXIS) OF GROUND MAT EXTENDED BEYOND CONCRETE LAYER ARE
LEFT FOR EXTENDING TO NEXT FLOOR ELEVATION FOR LAYING
 ANOTHER RING OF MAT AT THAT FLOOR FOR MAKING CONNECTIONS
TO EQUIPMENT AND SO ON.

12. DESIGN STEPS
 AREA OF CONDUCTOR,
𝐼 𝑆𝐶
𝐴
=
𝐾
𝑡 𝑐
𝐴 =
𝐼 𝑆𝐶× 𝑡 𝑐
𝐾
(AS PER IS: 3043 CL. NO 12.2.2.1)
 SPACING FACTOR FOR MESH VOLTAGE = Km
𝐾𝑚 =
1
2𝜋
ln
𝐷2
16ℎ𝑑
+
𝐷 + 2ℎ 2
8𝐷𝑑
−
ℎ
4𝑑
+
𝐾||
𝐾ℎ
ln
8
𝜋 2𝑛 − 1
 CHECK FOR ADEQUACY OF (L) FOR E STEP AND E MESH
 ESTEP (TOLERABLE) = ( RK +6CS X PS)… (AS PER EQ -30 OF
IEEE-80)

13. DESIGN STEPS
IK = CURRENT RMS FLOWING THRU BODY
WEIGHT 70KG= 0.157 / √ TS
RK IS THE RESISTANCE OF BODY IN OHMS = 1000 OHMS
 𝐸𝑆𝑡𝑒𝑝𝑐𝑎𝑙𝑐𝑢𝑙𝑎𝑡𝑒𝑑 =
𝐾𝑠 𝐾 𝐼 𝐼 𝑆𝐶 𝜌
𝐿
(As per Eq -33 of IEEE-80)
 𝐸 𝑇𝑜𝑢𝑐ℎ(𝑡𝑜𝑙𝑒𝑟𝑎𝑏𝑙𝑒) =
𝑅 𝐾+1.5𝐶𝑠 𝜌𝑠 0.157
𝑡𝑠
(As per Eq -80 of IEEE-80)
 CALCULATION OF GRID RESISTANCE (As per IS 3043 Cl No
9.2.3 )

𝑹 𝑮 =
𝟏𝟎𝟎𝝆
𝟐𝝅𝑳
𝒍𝒏 𝟒𝑳
𝒕
𝛀

14. S,No Details of Earthing System Resistance Symbols
1 Single Earth Electrode
𝑅 =
100𝜌
2𝜋
𝑙𝑛
4𝑙
𝑑
𝜌=Soil Res()
l=Length of strip(cm)
d= Dia of rod (cm)
2 Multiple Earth Electrode 𝑎 =
𝜌
2𝜋𝑅𝑖 𝑆
𝑅 = 𝑅𝑖
1 + 𝜆𝑎
𝑛
Ri=Resis of one rod in isol
𝜌=Soil Res()
n= Nos of rods
S=Dist between rods (m)
= Factor as per Table
3 Strip Conductor Earthing
𝑅 =
100𝜌
2𝜋
ln
2𝑙2
𝑤𝑡
𝜌=Soil Res()
l=Length of strip(cm)
W= depth of burial of
electrode (cm)
t=width (cm)
4 Earthing Plate
𝑅 =
𝜌
4
𝜋
𝐴
𝜌=Soil Res()
A= Area of both side of
Plate(m2)

15. Factor for Parallel Electrodes
No of Electrodes Factor
2 1.00
3 1.65
4 2.15
5 2.54
6 2.87
7 3.15
8 3.39
9 3.61
10 3.81

16. GROUND MAT IN POWER HOUSE
THE GROUNDING SYSTEM IN A POWER HOUSE
COMPRISES OF:
 GROUNDING SYSTEM FOR POWER HOUSE (PH)
 GROUNDING SYSTEM FOR SWITCHYARD (SY)

17. DESIGN ASPECT OF GROUND MAT
 LIMIT THE OVERALL POTENTIAL RISE.
 PROTECT PERSONNEL & DEVICES FROM OVER VOLTAGES.
 LOW IMPEDANCE PATH TO FAULT CURRENT FOR RELIABLE &
PROMPT OPERATION OF PROTECTIVE DEVICES DURING
GROUND FAULT.
 STEP POTENTIAL WITHIN THE PERMISSIBLE LIMIT.
 TOUCH POTENTIAL WITHIN THE PERMISSBLE LIMIT.

18.  SECURITY AND SAFETY FENCE AROUND SWITCHYARD.
 MANDATORY CONNECTING ALL THE METALLIC PARTS
OR STATIC PARTS OF ELECTRICAL EQUIPMENT
MINIMUM AT TWO POINTS.
 EARTHING OF LIGHTNING PROTECTIVE DEVICES.

19. DESIGN ASPECT OF GROUND MAT
 SOIL AND SURFACE RESISTIVITY
 SIZE( DEPENDING ON AREA) AND TYPE OF EARTH SYSTEM
 DEPTH OF BURIAL OF ELECTRODE
 MATERIAL OF GROUND MAT
 MOISTURE CONTENT OF THE SOIL.
 SHORT CIRCUIT RATING AND DURATION OF SHORT CIRCUIT
 DURATION OF SHOCK
 PERMISSIBLE GROUNDING RESISTANCE
 PERMISSIBLE TOUCH AND STEP POTENTIALS

20. DATA AND DESIGN
 THE FAULT LEVEL AT 33KV LEVEL (STEP UP VOLTAGE) HAS
BEEN CONSIDERED AS 31.5KA
 THE DESIGN OF EARTH MAT 60% OF 31.5 KA HAS BEEN
CONSIDERED IN ACCORDANCE WITH BS-7354-CLAUSE NO
7.3.2
 THE MATERIAL OF EARTH MAT HAS BEEN CONSIDERED AS
“COPPER FLAT” AND COPPER CLAD STEEL RODS

21. BASED ON THE AVAILABLE INPUTS,THE FOLLOWING PARAMETERS
HAVE BEEN CONSIDERED FOR PRELIMINARY DESIGN IN
ACCORDANCE WITH IEEE-80
INPUT DATA (Tiga Power House)
Sl. no Symbol Descriptions Values PH Values ODY Units
1 Isc Fault current (60% of 31.5kA) 18900 18900 Amps
2 ρ
Soil resistivity (average of P1 & P2
is 75.45Ω & 81.02Ω) 80 80 Ω-m
3 ρs Surface layer resistivity 3000 3000 Ω-m
4 D
Spacing between parallel
conductor 4 1.6 Metre
5 LPH Length of PH and ODY 36 41.6 Metre
6 BPH Breadth of PH and ODY 28 22.4 Metre

22. SUMMARY OF THE RESULT
Tolerable Calculated
Power House Step voltage
(ESTEP)
3938.839 V > 653.24 V
Touch
voltage(ETOUCH)
1151.23 V EMESH
calculated >
801.17 V
Switch Yard Step voltage
(ESTEP)
3938.83 V > 2204.41 V
Touch voltage
(ETOUCH)
1151.23 V EMESH
calculated >
685.02V
Grid resistance 0.117Ω

23. DESIGN AND ITS RESULTS OF GROUND MAT OF POWER HOUSE AFTER
EXCAVATION COMPLETED
INPUT DATA
Sl. no
Symbol Descriptions
Values PH
8MW & TRL
Values
PH-2MW
Values
ODY
Values SB &
SG room
Units
1 Isc Fault current (60% of 31.5kA) 18900 18900 18900 18900 Amps
2 Ρ Soil resistivity 670.5 112 112 112 Ω-m
3 ρs Surface layer resistivity 5000 5000 5000 5000 Ω-m
4 D
Equivalent Diameter of the grid
conductor 0.020 0.020 0.020 0.020 Metre
5 D
Spacing between parallel
conductor
1.5 3 4 4 Metre
6
L Length of PH, ODY & Service bay
including switch gear room
16.7 12 53.5
28
Metre
7
B Breadth of PH, ODY & Service bay
including switch gear room
23.4 23.4 38.75
23.4
Metre

24. SUMMARY OF THE RESULT
Location Particulars Tolerable Calculated Limits
Power House 8MW Step voltage (ESTEP ) 6483.32 V < 12590.27 V Unsafe
Touch voltage (ETOUCH ) 1787.35V < EMESH calculated 1952.42 V Unsafe
Grid resistance RG 0.364 Ω Safe
Power House 2MW Step voltage (ESTEP ) 6416.71V > 492.07 V Safe
Touch voltage (ETOUCH ) 1770.70V > EMESH calculated 396.784 V Safe
Grid resistance RG 0.061Ω Safe
Switch yard Step voltage (ESTEP ) 6416.71V > 715.70 V Safe
Touch voltage (ETOUCH ) 1770.70V > EMESH calculated 579.43 V Safe
Grid resistance RG 0.061 Ω Safe
Service bay & Switch
gear room
Step voltage (ESTEP ) 6416.71 V > 774.68 V Safe
Touch voltage (ETOUCH ) 1770.70V > EMESH calculated 540.62 V Safe
Grid resistance RG 0.061 Ω Safe

25. TO LIMIT THE STEP AND TOUCH POTENTIAL
WITH IN POWER HOUSE
 IN CASE OF HIGH RESISTIVITY SOIL, IT HAS BEEN REVEALED THAT IT
IS DIFFICULT TO MEET THE SAFETY CRITERIA OF TOUCH AND STEP
POTENTIALS.
 IT HAS BEEN FOUND THAT LARGE LAND AREA IS REQUIRED FOR
MEETING THE REQUIREMENT.
 FOR CONSIDERING THE COST EFFECTIVE SOLUTION, IT HAS BEEN
NECESSARY TO RE-EXAMINE THE REQUIREMENT

26. IEEE-665,GUIDE FOR GENERATING STATION
GROUNDING
 CL NO 5.1: GROUNDING PRINCIPLE STIPULATES THAT
TOUCH AND STEP POTENTIAL SHALL MEET THE
PERMISSIBLE LIMITS
 CL NO 5.2.7 STIPULATES THAT “THE MAXIMUM
ALLOWABLE TOUCH AND STEP VOLTAGES ARE THE
CRITERIA THAT SHOULD BE MET TO ENSURE A SAFE
DESIGN. IF THE TOUCH AND STEP VOLTAGES OF THE
GRID DESIGN ARE BELOW THE MAXIMUM VALUES, THEN
THE DESIGN IS CONSIDERED ADEQUATE.”

27. IEEE-665,GUIDE FOR GENERATING
STATION GROUNDING
 CL NO 5.2.2 STATES THAT GENERATING STATIONS DIFFER FROM
SUBSTATIONS IN THAT THE PERSONNEL TO BE PROTECTED ARE
GENERALLY WORKING INDOORS. BECAUSE THEY ARE NOT IN DIRECT
CONTACT WITH THE EARTH OR WITH A LAYER OF CRUSHED ROCK
COVERING THE EARTH, THEY ARE NOT EXPOSED TO MANY OF THE
STEP AND TOUCH VOLTAGE CONDITIONS THAT PERSONNEL IN
SUBSTATIONS ARE EXPOSED.
 THE CEA NOTIFICATION NO-211 DATED 20TH AUG 2010 ALSO STATES
THAT TOUCH AND STEP POTENTIAL SHALL BE MAINTAINED WITHIN
ACCEPTABLE LIMITS.

28. DELIBERATION
 ACCORDINGLY, TAKING COGNIZANCE OF
PRACTICES IN VOGUE IN VARIOUS HYDRO POWER
STATIONS, THE CRITERIA FOR STEP AND TOUCH
POTENTIAL HAS NOT BEEN IGNORED AND
ADOPTED AS CRITERIA FOR SAFE DESIGN BUT
THIS NEEDS TO BE DELIBERATED IN THE
CONFERENCE.

29. SURFACE LAYER RESISTIVITY
 IN THE PRELIMINARY DESIGN CALCULATIONS, THE SURFACE LAYER
RESISTIVITY WAS CONSIDERED AS 5000 Ω- M.
 THE VALUES INDICATED FOR DRY AND WET CONDITIONS FOR THE
VARIOUS SURFACE MATERIALS ARE WIDELY VARYING VIZ: FOR
CONCRETE UNDER DRY CONDITION IT IS 1X106 TO 1X109OHM-M AND
21 TO 100 OHM-M FOR WET CONDITIONS.
 IT IS ALSO INDICATES THAT 1X109 IS USED FOR OVEN DRIED
CONCRETE.
 THE VALUE OF 10,000 Ω M WAS CONSIDERED AS CONCRETE MAY NOT
BE FULLY DRIED AT MIV FLOOR LEVEL.

30. FINAL DESIGN OF GROUND MAT OF POWER HOUSE
 MAIN PURPOSE OF THIS REWORK HAS BEEN TO UNDERTAKE SAFE
DESIGNING AND COST EFFECTIVE GROUNDING SYSTEMS FOR TIGA HEP.
 TO ADOPT SAFE LIMITS OF TOUCH AND STEP POTENTIAL INSIDE THE
POWER HOUSE WITHOUT SATELLITE GRID STATION AND SAVE COST.
 TO CONSIDER SURFACE RESISTIVITY VALUE OF CONCRETE AS 10,000 Ω
INSIDE THE POWER HOUSE AND THAT OF WASHED QUARTZ AS 5,000 Ω IN
SWITCH YARD. WITH THE CHANGE IN THE SURFACE RESISTIVITY VALUES,
THE SAFE LIMITS OF E TOUCH AND E STEP OF EARTH MAT WERE ALSO
ACHIEVED IN 8MW PORTION OF POWER HOUSE AND THIS ALSO
RESULTED IN REDUCTION IN THE MATERIAL REQUIRED FOR EARTH MAT.

31. FINAL DESIGN OF GROUND MAT
INPUT DATA
Sl. no Symbol Descriptions Values
PH 8MW
& TRP
Values
PH-
2MW
Values
ODY
Values SB &
SG room
Units
1 Isc
Fault current (60% of
31.5kA) 18900 18900 18900 18900 Amps
2 ρ Soil resistiviy 670.5 112 112 112 Ω-m
3 ρs Surface layer resistivity 10000 10000 5000 10000 Ω-m
4 D
Spacing between parallel
conductor
1.5 3 4 4 Metre
5
L
Length of PH, ODY &
Service bay including
switch gear room as per
excavated profile
82.3 12.8 53.5 28.5 Metre
6
B
Breadth of PH, ODY &
Service bay including
switch gear room
22.5 22.5 38.75
22.5
Metre

32. SUMMARY OF THE RESULT
Location Particulars Tolerable Calculated Limits
Power house 8MW Step voltage (ESTEP ) 12619.39
V
> 7886.36 Safe
Touch voltage (ETOUCH ) 3319.37 > EMESH
calculated
1692.44 Safe
Grid resistance RG 0.42 Ω Safe
Power house 2MW Step voltage (ESTEP ) 12611.39V > 351.90 Safe
Touch voltage (ETOUCH ) 3319.37 > EMESH
calculated
340.97 V Safe
Grid resistance RG 0.053Ω Safe
Switch yard Step voltage (ESTEP ) 6466.71 > 488.51V Safe
Touch voltage (ETOUCH ) 1170.78V > EMESH
calculated
501.60 V Safe
Grid resistance RG 0.053 Ω Safe
Service bay & Switch
gear room
Step voltage (ESTEP ) 12611.39
V
> 346.56 V Safe
Touch voltage (ETOUCH ) 3319.37 > EMESH
calculated
414.18 Safe

33. ISSUES FOR DELIBERATION OF CONFERENCE
 THE DESIGN OF GROUNDING MAT OF POWER HOUSES AND EHV
SUBSTATIONS IS CARRIED OUT LARGELY BASED ON IEEE80-2000
INCLUDING POWER HOUSE PROVISIONS OF IEEE 665-1997. THE
DESIGN OF GROUND MAT ATTAINS CRITICALITY WHEN SOIL
RESISTIVITY IS HIGH AND INHERITED SMALL GROUND AREA IN
CASE OF SMALL POWER HOUSES (SPH). THE FOLLOWING TOPICS
ARE LISTED FOR CONSIDERATION OF THE INTERNATIONAL
CONFERENCE

34. SOIL RESISTIVITY
 UNIFORM SURFACE RESISTIVITY MEASURED AT THE SURFACE OF
POWER HOUSE AND SWITCH YARD WITH CONVENTIONAL METHOD OF
MEASUREMENT (80 OHM-M)]
 AS THE EXCAVATION AT HIGHER LEVEL FOR 2MW GEN UNIT AND 8MW
GEN UNIT WAS COMPLETED AND SOIL RESISTIVITY WAS MEASURED AT
BOTH THE GEN UNITS LEVELS, SWITCHGEAR CONTROL & SERVICE
BAY AND ODY
 THE SOIL RESISTIVITY AT ALL LOCATIONS EXCEPT 8MW UNIT WAS
MEASURED AS 120 OHM-M WHEREAS SOIL RESISTIVITY AT 8MW UNIT
WAS MEASURED AS 670 OHM-M.
THIS WAS COMPARATIVELY HIGH SOIL RESISTIVITY AND SMALL POWER
HOUSE SURROUNDED AREA

35. DESIGN OF GROUND MAT
 IN IEEE 665, THE SAID STANDARD DOES NOT INSIST FOR
MEETING TOUCH AND STEP POTENTIAL REQUIREMENT INSIDE
POWER HOUSE.
 OPERATORS DURING WORKING IN THE POWER HOUSE DONOT
STEP OUT OF POWER HOUSE AND DANGER OF DIFFERENT
VOLTAGE GRADIENT CAN BE AVOIDED BY PROVIDING SOME
ROUNDS OF GROUNDING MATERIAL (COPPER) AROUND THE
POWER HOUSE.
 THIS IS SIMILAR TO EXTENDING THE GROUND MAT OF S/S
OUTSIDE THE FENCE TO PROTECT FROM DANGEROUS VOLTAGES
WHEN UN-AUTHORIZED PERSONNEL TOUCH THE FENCE FROM
OUTSIDE.

36.  IT WAS CONSIDER TO USE SURFACE RESISTIVITY OF CONCRETE AS
10,000 OHM-M INSTEAD OF 5000 OHM-M. ON REVISION OF
CALCULATION IT HAS BEEN OBSERVED THAT TOUCH AND STEP
POTENTIAL AT ALL THE LOCATIONS MEET THE SAFE REQUIREMENT.
 IT IS CONVENIENT FOR DESIGNER TO ADOPT 5000, 10,000OHM-M OR
MORE AS THE SURFACE RESISTIVITY OF CONCRETE TO ACHIEVE TOUCH
AND STEP POTENTIAL LIMITS THOUGH CONCRETE IS PROVIDED IN
EVERY POWER HOUSE
 GROUND RESISTANCE VALUE WHEN CALCULATED FOR EACH PORTION
OF POWER HOUSE AND SWITCHYARD ARE WITHIN PERMISSIBLE LEVEL.
WHEN CONNECTED TOGETHER AND RESISTANCE MEASURED, THE
AVERAGE VALUE MAY BE FURTHER LESS.

37. REFERENCE
 IEEE 80-2000: GUIDE FOR SAFETY IN AC SUBSTATIONS GROUNDING
 IEEE 665-1995 : GIDE FOR GENERATING STATIONS GROUNDING
 BS 7430-1998 : CODE OF PRACTICE FOR EARTHING
 IS 3043 AS AMENDED : CODE OF PRACTICE FOR EARTHING COVERING
ELECTRICAL INSTALLATIONS
 CBI&P PUBLICATION NO 223 : DESIGN OF EARTHING MAT OF HIGH VOLTAGE
SUBSTATIONS
 NATIONAL ELECTRICAL SAFETY CODE ( NESC) -1990, 1997,2002 AND 2012
 IE RULES 1956 AND ELECTRICITY ACT 2003
 IACSIT International Journal of Engg Techn. Vol 4 No.3, June 2012,
Earthing System Design of Small Hydro Power (SHP) Stn – A Rewiew
By M.K.Singhal, S.N Singh