importance of grounding in power systemssolarbaba.in/pdf/earthing system.pdf · manual on earthing...

Importance of Grounding in Power Systems

Objective of Earthing

Prime Object of Earthing is to Provide a Zero Potential Surface in and around and under the area where the electrical equipment is installed.

Earthing is essential at every stage of electricity generation, transmission and utilization

Importance of Earthing

Personal Safety

Protection of Equipment : Prevent or at least minimize damage to equipment as a result of heavy fault current and lightning thus improve the reliability of equipment

Protection of System : Improve the reliability of power supply.

Earthing Standards

IS: 3043 : 1966, 1987 reaffirmed 2006 Code of Practice for Earthing. Indian Electricity rules 1956 (as amended up to 2000) IS: 2309 1989 (reaffirmed 2005) Protection of Buildings and allied Structures

against lightning – Code of Practice. IS : 2689: 1989 (reaffirmed March 2010): Guide for Control of Undesirable

static Electricity. Manual on Earthing of AC Power Systems : CBIP Publication No.302 : 2007

and 311 BS: 7430 : 1998, Code of Practice for Earthing.( formerly CP 1013: 1965)

British Standard Institution London 1992 BS: 6651: 1992, Protection of Structures. Against Lightning. IEEE :80 : 2000( Revision of IEEE Std 80: 1986) Guide for Safety in AC

Substation Grounding IEEE :142 :2007(Revision of IEEE Std 142 :1991) Grounding of Industrial

and Commercial Power System. IEEE 1100 : 2005 (Revision of IEEE Std 1100 : 1999) Powering and

Grounding Electronic Equipment

Types of Earthing

Types of Earthing

Plate Earthing

Pipe/Rod earthing

Strip earthing

Mat earthing

Plate Earthing

Plate earthing: Standard 1.2 mtr X 1.2 mtr

Generally only 0.6 mtr X 0.6 mtr is used

References IS 3043 :1987 Clause 9.2.1 page 19 IEEE 80 : 2000 Clause 14.2 ( 50) Page. 64

Material Thickness Corrosion

Copper 3 mm 0.2 % / yr

GI 6 mm 0.5 % / yr

Cast Iron 12 mm 2.2 % / yr

Plate earthing - Calculations

Ground Resistance (Rg) can be calculated as below

Considering a plate of 600 mm X 600 mm

Considering a plate of 1200 mm X 1200 mm

A

Rg

4ρ = Resistivity of the soil (assumed uniform) in ohm-m A = Area of the Plate (both sides)

52.22 62.088856892572.04

100XRg

26.11 81.044428442588.24

100XRg

Pipe / Rod Earthing

Pipe / Rod Earthing: Standard 3 mtr long

References IS 3043: 1987 Clause 9.2.2 page 20

Pipe/Rod Earthing - Calculations

Ground Resistance (Rg) can be calculated as

Considering ρ = 100 Ω-m, l = 300 cm, d = 4 cm

d

ln

lRg

4log2

100

ρ = Resistivity of the soil (assumed uniform) in ohm-m l = Length of the pipe/rod buried in the earth (in cm) d = Diameter of the pipe/rod ( in cm)

30.26 55.70378247 x 5.3051647743004log

3002100100 X

nXX

XRg



Change in Resistance between 40 mm & 80 mm diameter pipe/rod is

= 30.26 – 26.58 x 100 = 12.16 % 30.26 Hence, doubling the diameter decreases the Ground

resistance by 10 to 12%

26.58 45.01063529 x 5.3051647783004log

3002100100 X

nXX

XRg




Change in resistance when the length is doubled = 73.29 – 42.16 = 42.47 % 73.29 Change in resistance when the length is increased to 3 mtr = 73.29 – 30.26 = 58.71 % 73.29

73.29 4.60517018 x 15.915494341004log

1002100100 X

nXX

XRg

42.16 5.29831736 x 7.9577471542004log

2002100100 X

nXX

XRg

Doubling the Length of burial decreases resistance by 40% and trebling the length of burial decreases the resistance by 60%

Pipe/Rod Electrode - Calculations

Calculation using BS 7430 IEEE 80 : 2000 clause 14.6 (59) page 71

Change in Rg between IS & BS/IEEE standards is = 30.26 – 28.63 = 5.39% 30.26

]1)8([log2 d

ln

lRg

ρ = Resistivity of the soil (assumed uniform) in ohm-m l = Length of the pipe/rod buried in the earth (in m) d = Diameter of the pipe/rod ( in m)

28.63 5.39692965 x 5.3051647

]1)04.0

38([log32

100 Xn

XRg

Strip Earthing

Reference IS 3043 :1987 Clause 9.2.3 page 21

The ground resistance is calculated using

Combinations between strip & pipe/rod earthing can be done

wt

ln

lRg

22log2

100

ρ = Resistivity of the soil (assumed uniform) in ohm-m l = Length of the strip buried in the earth (in cm) w = depth of the burial (in cm) t = width of the strip (in cm) (incase rod is used, t = 2d)

Mat earthing

Is the combination of Strip & Rod earthing

Reference IEEE 80 : 2000 Clause 14.2 ( 51) Page 64 (Laurent & Newmann) IEEE 80 : 2000 Clause 14.2 ( 52) Page 65 (Sverak)

Earth resistance can be calculated using Laurent & Niemann method as below

Earth resistance can be calculated using Sverak method as below

TT

glAlr

R

44

)]/201

11(2011[

AhAlR

Tg

ρ = Resistivity of the soil (in ohm-m ) A = area of the station (in sq mtr) lT = Total length of the conductor (both strips & rods)

Calculation of Ground resistance of Grid Electrode

With-out & with ground electrodes

Considering Building of 80 m X 40 m, 50 mm X 6 mm GI strips laid 0.5 mtr depth & 1 mtr around the building

Total Length of Strip = 2 ( L + b ) = 2(81+41)= 244m

Soil Resistivity = 100 Ω–m

TT

glAlr

R

44


Using Laurent & Niemann method, Rg is calculated as below

With 24 nos of 3 mtr long 40 mm dia electrodes are connected to above mat at suitable places. The Ground resistance is

= 0.76891884 +100/(244+72)

= 0.768918845 + 0.316455696

= 1.085374541

178.10.40983606 0.76891884

244100

41814100

44

X

lAlrR

TTg


Using Sverak method, the earth resistance is calculated as below

With 24 nos of 3 mtr long 40 mm dia electrodes are connected to

above mat at suitable places. The Ground resistance is = 100 [ 1/(244+72) + 0.00761540 ]

= 100 [0.010779956]

= 1.0779956

1.1713762)0.01171376 ( 100

)0.00761540 0.00409836 (100

)]4181/205.01

11(418120

12441[100

)]/201

11(2011[

XXX

AhAlR

Tg

Comparison of Results

Ground Resistance

L&N Sverak Difference Difference (in %)

Without Ground Rods

1.178754911 Ω

1.1713762

0.00737871Ω

0.54%

With Ground Rods

1.085374541 Ω

1.0779956

0.00737894 Ω

0.68%

Note: Hence, in a large mat earthing system, ground rods plays no major role. Only area plays a major role.

Example: In Order to achieve the Ground Resistance of One Ohm for Substations ( Soil Resistivity 100 Ω – m ) of above 33 KV, r ( equivalent radius ) shall be not less

than 25 mtrs. Π r 2 (area of the substation ) shall be Π x 25 x 25 = 1963.5 m2 .

Ground resistance by Schwarz’s method

Reference IEEE 80:2000 Clause 14.3 (53) Page 66

Earth Resistance is calculated using the formula below

1221

21

2

2

12

RRR

RRRRg

R1 = Ground Resistance of gird conductors in Ω R 2 = Ground Resistance of all ground rod in Ω R12 = Mutual Ground Resistance between the group of gird conductors R1 & group of ground Rods R2 in Ω

Soil Resistivity Measurement

Type of Earth testers

Make Model

Megger DET 2/2 UK.

Fluke 1623 & 1625 USA / UK with current clamps.

Chauvin Arnoux 6460, 6462 & 6470 FRANCE / UK with current clamps.

Kew (Kyoritsu) 4106 JAPAN/ with current clamps.

Comparison of Analog & Digital Testers

Parameters Analog meter Digital meter

Accuracy

5% of full scale and shall be effective above 25% of full scale. At 25% of reading absolute error is 20%. Not accurate and low resolution

2% of reading in entire range hence very accurate and high resolution

Voltage 250V hand cranking Micro processor based 30 to 50 V automatic reading

Frequency Fixed (60 to 90 HZ) Variable. In auto mode it selects test frequency with least amount of noise

High Spike resistance Do not indicate Displays the high spike resistance.

Open circuit Do not indicate

Displays current circuit open/potential circuit open

Factors Affecting the Soil Resistivity

Type of the soil.

Moisture.

Dissolved salt in water.

Temperature.

Grain size and its distribution.

Seasonal variation.

Artificial treatment.

Effect of Earth Layers

The measured apparent Resistivity depends on the Resistivity of the various materials through which the current passes, it is an average of all those Resistivities.

As the electrode spacing is increased, the current flows through a great volume of material; both, horizontally and vertically, and the deeper materials will have an effect on the apparent Resistivity.

Thus, if the deeper material is of higher Resistance(lower Conductance), the current flow lines will be deflected up-wards, and the current density in the near surface volume element will be increased.

If the deeper material is of lower Resistivity (higher Conductance), the current flow lines will be deflected down-ward and the current density will be decreased.

Methods of measuring soil resistivity

Equally spaced or Dr F.Wenner arrangement Reference

Clause 36 Page 77 to 79 IS3043 : 1987

Clause 7 .2.4 (1) Page 14 & 15 IEEE 81: 1983

Clause 9.2.1 Page 113 &114 CBIP PP No: 302

Clause 9.2.1 Page 113 &114 CBIP PP No: 302

Page .6 LEM

Unequally spaced or Schelumberger – Palmer Arrangement Reference

Clause 7 .2.4 (2) Page 15 IEEE 81: 1983

Clause 9.2 Page 116 CBIP PP No: 302

Central Electrode Method Reference

Clause 9.4 Page 124,125 CBIP PP No: 302

Equally spaced (Dr F. Wenner arrangement)

ρ= 2 AR -M

Unequally spaced

(Schlumberger – Palmer Arrangement)

ρ = C ( C+d) * R / d -M

Procedure for measuring Soil resistivity

A. For measuring soil resistivity at the site of a sub-station, measurements of resistivity are made along a number of radials of different locations, in the station area such that the whole area in which the earth electrodes are to be laid is covered. There ought to be a minimum of two radials at one location.

B. Spacing between the probes, which are hammered into the soil, shall be varied from the smallest value of about 0.5m or 1.0m to large value depending on the extent of the earth electrode and the conditions on the ground. Typically, if the extent of the station is 100m – 150m in the direction of the radial, the reading of the resistivity may be taken for probe spacing of 1m, 2m, 5m, 10m, 20m and 35m depending on the available space. The largest spacing may even be increased to 100m or more.


c. In case the resistivity variation is large, at least five progressively increasing probe spacings are necessary to get good estimate of deeper layer parameters.

d. A few spoonfuls of water may be poured around the probe, which has been hammered into ground, to get good conductive connection between probe and soil around it.

e. The soil along the radials shall be free from buried conductive pipes, etc., and it shall not be recently filled and therefore not yet compacted.

f. In case the grid conductors have already been installed, resistivity measurements except those for small probe spacing in center of large meshes shall be affected. If soil is homogenous, measurements may be made outside the grid


g. In case the earth at the site of measurement is rocky, it may not be possible to hammer the probes into ground, if attempt is made to hammer a probe into ground, cracks may develop around the point of entry of the probe into ground. This results in high contact resistance in the current or the potential loop and shall result in erroneous results. A good digital earth tester shall have an indicator for high current loop resistance or high contact resistance at potential probes. If cracks develop around the probe, the hole shall be filled with wet mud and the probe shall be stood in the mud. In case probes cannot be hammered into ground, holes shall be drilled into ground and these may be filled with mud or cement or Bentonite slurry into which the probes are erected.

h. Test wires shall be insulated and shall not have joints in between. These shall be firmly connected to terminals of earth resistance meter and test electrodes.

i. As far as possible wires from potential terminals may not run parallel to and near those from current terminals.


j. Test electrode shall be clean and free from rust.

k. Hammering of electrodes shall not result in loosening of connection between electrode and its test leads and thereby an increase of contact resistance between test lead and electrode.

l. Local soil condition such as surface rock, loose soil, water logging, roadside, etc., at measurement point shall be recorded in measurement book for ease of interpretation of measured data.

m. Resistivity value shall be calculated after each observation. In case there is an abrupt variation in measured resistivity, measurement for that probe spacing shall be repeated after altering the probe location.

n. Accuracy of earth resistance meter shall be checked before and after the measurements as per procedure given under:

Alternative electrode connection

Electrode Arrangement Resistivity Formula

C P P C ρ = 2πaR1

P C C P

C C P P ρ = 6πaR2

P P C C

C P C P ρ = 3πaR3

P C P C

As long as the electrode spacing is kept constant, the above equation is independent of the positions of the electrodes and is not affected when the current & potential electrodes are interchanged

E.g CPPC to PCCP (or) CCPP to PPCC (or) CPCP to PCPC

Comparison of Wenner & Schlumberger Methods

Interpretation of the reading is more complicated. A more sensitive instrument is required for the

Schlumberger configuration than for the Wenner arrangement

The Wenner arrangement is probably more suitable for the non specialist and the occasional user of Resistivity surveys

Schlumberger method is more faster than Wenner’s method since only two electrodes position have to be changed. I.e, Current electrodes

Case Study 1

Consider ρ = 2 AR -m

A= Distance between adjacent electrode (m),

R = Earth tester reading

Sl No. A (mtr) R () Ρ (-m) 1 2 4.33 54.412

2 3 2.60 49.009(min)

3 4 2.35 59.062

4 5 1.986 62.392

5 6 1.652 62.279

6 7 1.462 64.301

7 8 1.305 65.593(max)

• ρ Average 59.579 • 130% of ρ Ave = 1.3 x 59.579 = 77.453 • 70% of ρ Ave = 0.7 x 59.579 = 41.705 • Minimum & Maximum value lies within 41.705 and 77.453 • The Soil is Homogeneous.

Case Study 2

Site of 120 MW Diesel Power Plant at Yelahanka, Bangalore

Location Yelahanka Site Size 92.12m x 73.15m

Date of Measurement

23.01.91

Type of soil Agriculture Land

Condition of Ground

Dry

Earth tester used ET3/2

A1 D1 B1 D2 C1 C2 B2 A2

Case Study 2 - calculations

Inner- Electrode Spacing

Megger Reading in ohms (Soil Resistivity = 2πaR in ohm-m)*

2.5m 5m 7.5 10m 15m

Location A1-A2 2.0 Ω

(31.42)

1.03 Ω

(32.36)

0.94 Ω

(44.30)

0.72 Ω

(45.32)

0.52 Ω

(49.02)

Location B1-B2 1.74 Ω

(27.33)

0.94 Ω

(29.53)

0.83 Ω

(39.11)

0.62 Ω

(38.96)

0.52 Ω

(49.02)

Location C1-C2 1.03 Ω

(32.36)

0.61 Ω

(28.74)

0.61 Ω

(38.33)

0.51 Ω

(48.07)

0.51 Ω

(48.07)

Average of the above 37.99 ohm-meters Minimum Resistivity Encountered 27.33 ohm-meters Maximum Resistivity Encountered 49.02 ohm-meters Conclusion: since the maximum and minimum resistivity lies within 30% of the average value the soil is a homogeneous one The soil is said to be homogenous when the average valuof ‘ρ’ lies within 30 percent

Comparison between Wenner & Schelumberger methods

Distance

Between

adjacent

Electrodes (m)

Earth Tester

reading (Ω)

Soil resistivity

(Ω -m)

ρ = 2πAR

1m 12.29 77.220

2m 7.65 96.130

3m 4.54 85.577

4m 3.68 92.488

5m 3.10 97.389

6m 2.34 89.347

7m 2.22 97.640

8m 2.10 106.060

Average 92.731

Wenner Method

130% of 92.731 = 120.50 70% of 92.731 = 64.912

Lowest value is 77.220Ω-m which is above 64.912Ω-m

Highest value is 106.060Ω-m

which is lower than 120.550Ω-m

Hence the soil is homogenous with soil resistivity of 92.73Ω -m

Comparison between Wenner & Schelumberger methods

Schelumberger Method Distance between potential & Current electrode (P1 to C1 & P2 to C2)CMtrs

Earth tester reading Ω Soil resistivity ρ = πc (c+d) x R d Ω-m

1 12.30 77.283

2 4.65 87.650 3 2.76 104.049

4 1.396 87.714

5 0.967 91.138 6 0.714 94.210

7 0.538 94.650

8 0.432 97.716 9 0.345 97.456

10 0.266 91.923

Average 92.388Ω-m

Central Electrode Method

c

b

a

s s s

Earth Tester

ground

d p P 1 P2 C2

C1

Central Electrode Method

In this method, two current electrodes are buried a large distance apart. The two potential electrodes are placed at distances ‘a’m and ‘b’m from one of the

current electrodes as shown in previous slide. The distance ‘c’ between current electrodes shall be about 10 times the distance ‘b’

or more. ρ = 2π ab R (b-a) Where ‘R’ is the meggar reading in ohms. In this method only the current electrode and the two potential electrodes buried

near it are to be in a straight line, the far current electrode is buried at a radial distance ‘c’ from the first current electrode and need not be in a straight line with the other three electrodes. The soil resistivity is obtained to a depth of approximately (a+b) / 2 m from the surface where the first three electrodes are buried.

If any observed soil resistivity for a probe spacing is found to be too high or too low

compared with resistivity for the next larger probe spacing along that radial, it may be judiciously ignored when determining the soil model

Case Study 1

Conducted in Nainital on 02/06/2010

Consideiring A = 1m, B = 2m, C = 20m

5 m

5 m 5 m

65.0

65.7

65.5

65.2

65.4 C

2π (1 x 2 ) x 65 = 816.814 Ω - m 2 - 1 Depth = (1+2) = 1.5 m 2

Measurement of Ground Resistance

Factors impacting grounding system

Water table variations will occur due to seasonality.

Corrosion of the grounding conductors and materials.

Contamination of the soil and surroundings from spillage such as chemicals, oils (1500 x 10¹² for new oil and 45 to 100 x 10¹² for old oil), acid, etc.

Mechanical Integrity

Electrical Integrity

Improper Maintenance.

Measurement Pre-requisites

Clean the electrode thoroughly and check the continuity to the opposite side of the electrode

Measure the voltage between C1P1 and P2 or C1P1 and C2. The voltage should not exceed the limit mentioned in the catalogue of the Earth Tester

The thumb rule is; the remote electrode shall be 10 times the depth of the burial of the electrode or 10 times the longest distance in the earth-mat or any configuration

Precautions to be taken for Measuring Ground Resistance

Avoid taking measurement during cloudy day There is a possibility of lethal potential existing between a station

ground & a remote Ground. If a system fault involving the station ground occurs while ground

resistance is being measured. The use of Rubber gloves is advisable while making connections to the test electrode.

Under no circumstances should the two hands or other part of the body of the testing personal should be allowed to complete the circuit between the points of possible high potential difference.

An isolated lightning arrester ground should never be tested with the arrester in service , because of the possible high potential gradients around the ground connection.

Since the resistivity of the upper soil layers is greatly influenced by weather , a day test should be chosen which is free from extreme weather conditions.

Methods of measuring Ground Resistance

Fall of potential method

Clause 37.1 Page 79 IS3043 : 1987

Clause 8.2.1.5 Page 20 & 21 IEEE 81: 1983

Clause 10.4 Page 140 &141 CBIP PP No: 302

Page.7 LEM

Selective Method using current clamp page.8 LEM

Stakeless Method using current clamps

Page. 10 of LEM

Clause 8.2.1.1, & 8.2.1.2 Page 19 of IEEE STD 81 – 1983.

E. B. Curdt’s method

Clause 8.2.1.6 Page 22 IEEE 81: 1983

Clause 10.4.7 Page 141 & 142 CBIP PP No: 302

Slope method

G.F. TAGG Resistance measurement of Large grounding system

IEE.VOL.77 No11 Nov.1979

IS: 3043 Alternate method:

Clause 37.2 Page 79 IS3043: 1987

Fall of Potential Method

Common Sources of Errors in Fall of Potential Method

a. Inadequate separation of the unknown and auxiliary electrodes. b. Operation of Instrumentation at inadequate sensitivity level. c. Location of auxiliary current electrodes or potential probes in the

vicinity of buried metallic structures. d. Inductive coupling between voltage and current leads. e. Excessively high current probe resistance which can lead to

parasitic capacitance and resistance errors f. Incorrect interpretation of fall-of-potential data. g. Un-calibrated instrumentation. e. As experience is gained, short cuts or simplifications can be made

where it is known that the accuracy of the results will not be significantly affected.

f. It is usually useful to take readings at relatively large potential probe intervals initially and then to take intermediate readings where an apparent knee or “FLAT SPOT” in the curve has been observed.

Earth Resistivity Curve

Resistance

Arbitrary Position of E electrode 0.2 EC 0.4EC 0.6EC Position of

C electrode

Position of P electrode measured from E.

Earth Resistance Curve

Slope Method

Was established by Dr. G.F. Tagg. The following is the summary of the paper published in IEE 1970.(Vol. No. 177, No. 11)

This technique shall be used when testing earth electrode systems which covers a large area.

This method is useful when the position of the centre of the earthing system is either unknown or inaccessible (e.g. if the system is beneath the floor of a building). This method yields results of greater accuracy than those detailed above.

Slope Method - Procedure

The procedure is as follows: A) The terminals C1 & P1 on the instruments are connected to the earth

electrode. B) Connect terminal C2 to a current electrode inserted in the ground 50m

more or away. The distance from the earth electrode to the current electrode is EC.

c) The potential electrode connected to terminal P2, is inserted at several positions between the earth and current electrodes, starting from near the earth electrode. (The electrodes must be in a straight line). At each position the resistance is measured and the earth resistance curve is plotted from the results e.g., (as shown in fig) at least 6 readings are needed. Drawing the curve will show up any incorrect points which may be either rechecked or ignored

D) From the curve the equivalent reading to potential electrode position 0.2EC, 0.4EC & 0.6EC can be found. These becomes R1, R2 & R3 respectively.

E) Calculate the slope co-efficient µ. Where µ= R3-R2 R2-R1

Slope Method - Procedure

F) µ is the measure of the change of slope of the earth resistance curve. From the table shown in the next page, obtain the value of PT /EC for this value of µ. PT is the distance to the potential electrode at the position where the true resistance

would be measured.

G) Multiply the value of PT /EC by EC to obtain the distance P2. H) From the curve, again read off the value of resistance that

correspond to this value of PT. The value obtained is earth system resistance.

It is important to note that: If the value of µ obtained is not covered in the table, then the current

electrode will have to be moved further away from the earthing system. If it is required, further sets of test results can be obtained with

different values of EC, or different directions of the line of EC. From the results obtained of resistance for various values of the

distance EC a curve may be plotted.

Slope Method

This shows how the resistance is decreasing asymptotically as the distance chosen for EC is increased.

The curve indicated that the distances chosen for EC in tests(1) and (2) were not large enough; and that those chosen in tests(3) and (4) were preferable because they would give the more correct value of the earth resistance.

It is unreasonable to expect an accuracy of readings of more than 5%, 10% is often adequate bearing in mind that this sort of variation could easily occur with varying soil moisture conditions or non-homogeneous soils.

Chart for use with slope method is in Annexure II (next slides).

0 1 2 3 4 5 6 7 8 9

0.40

0.41

0.42

0.43

0.44

0.45

0.46

0.47

0.48

0.49

0.6432

0.6418

0.6403

0.6389

0.6374

0.6360

0.6346

0.6331

0.6317

0.6302

6431

6416

6402

6387

6373

6359

6344

6330

6315

6301

6429

6415

6400

6386

6372

6357

6343

6328

6314

6300

6428

6413

6399

6384

6370

6358

6342

6327

6312

6298

6426

6412

6397

6383

6369

6354

6340

6325

6311

6297

6425

6410

6396

6382

6367

6353

6338

6324

6310

6295

6423

6409

6395

6380

6366

6351

6337

6323

6308

6294

6422

6408

6393

6379

6364

6350

6336

6321

6307

6292

6420

6406

6392

6377

6363

6348

6334

6320

6305

6291

6419

6405

6390

6376

6361

6347

6333

6318

6304

6289

0.50

0.51

0.52

0.53

0.54

0.55

0.56

0.57

0.58

0.59

0.6288

0.6273

0.6258

0.6242

0.6227

0.6212

0.6197

0.6182

0.6166

0.6151

6286

6271

6256

6241

6226

6210

6195

6180

6165

6150

6258

6210

6255

6239

6224

6209

6194

6179

6163

6148

6283

6268

6253

6238

6223

6207

6192

6177

6162

6147

6282

6267

6252

6236

6221

6208

6191

6176

6160

6145

6280

6265

6252

6235

6220

6204

6189

6174

6159

6144

6279

6264

6248

6233

6218

6203

6188

6172

6157

6142

6277

6262

6247

6232

6217

6201

6186

6171

6156

6141

6276

6261

6245

6230

6215

6200

6185

6169

6154

6139

6274

6259

6244

6229

6214

6198

6183

6168

6153

6138

0.60

0.61

0.62

0.63

0.64

0.65

0.66

0.67

0.68

0.69

0.70

0.71

0.72

0.6136

0.6120

0.6104

0.6087

0.6071

0.6055

0.6039

0.6023

0.6006

0.5990

0.5974

0.5957

0.5940

6134

6118

6102

6086

6070

6053

6037

6021

6005

5989

5973

5955

5938

6133

6117

6100

6084

6068

6052

6036

6019

6003

5987

5971

5953

5936

6131

6115

6099

6083

6066

6050

6034

6018

6002

5985

5969

5952

5935

6130

6113

6097

6081

6065

6049

6032

6016

6000

5984

5967

5950

5933

6128

6112

6096

6079

6063

6047

6031

6015

5998

5982

5964

5948

5931

6126

6110

6094

6076

6061

6045

6029

6013

5997

5980

5964

5947

5930

6125

6108

6092

6076

6060

6044

6027

6011

5995

5979

5962

5945

5928

6123

6107

6091

6074

6058

6042

6026

6010

5993

5977

5960

5943

5926

6121

6105

6089

6073

6057

6040

6024

6008

5992

5976

5959

5942

5924

0.73

0.74

0.75

0.76

0.77

0.78

0.79

0.5923

0.5906

0.5889

0.5871

0.5854

0.5837

0.5820

5921

5904

5887

5870

5853

5835

5818

5920

5902

5885

5868

5851

5834

5817

5918

5900

5883

5866

5849

5832

5815

5916

5899

5882

5865

5847

5830

5813

5914

5897

5880

5863

5846

5829

5812

5912

5895

5878

5861

5844

5827

5810

5911

5894

5877

5859

5842

5825

5808

5909

5892

5875

5858

5841

5824

5806

5907

5890

5873

5858

5839

5822

5805

0.80

0.81

0.82

0.83

0.84

0.85

0.86

0.87

0.88

0.89

0.5803

0.5785

0.5766

0.5748

0.5729

0.5711

0.5692

0.5674

0.5655

0.5637

5801

5783

5764

5746

5727

5709

5690

5672

5653

5635

5799

5781

5762

5744

5725

5707

5688

5670

5851

5633

5797

5779

5760

5742

5723

5705

5686

5668

5650

5631

5796

5777

5759

5740

5722

5703

5685

5666

5648

5629

5794

5775

5757

5738

5720

5701

5683

5664

5646

5627

5792

5773

5755

5736

5718

5699

5681

5662

5644

5625

5790

5772

5753

5735

5716

5698

5679

5661

5642

5624

5788

5770

5751

5733

5714

5696

5677

5659

5640

5622

5786

5768

5749

5731

5712

5694

5675

5657

5638

5820

0.90

0.91

0.92

0.93

0.94

0.95

0.96

0.97

0.98

0.99

0.5618

0.5598

0.5578

0.5557

0.5537

0.5517

0.5497

0.5477

0.5456

0.5436

5616

5596

5578

5555

5535

5515

5495

5475

5454

5434

5614

5594

5574

5553

5533

5513

5493

5473

5452

5432

5612

5592

5572

5551

5531

5511

5491

5471

5450

5430

5610

5590

5570

5549

5529

5509

5489

5469

5448

5428

5608

5588

5588

5547

5527

5507

5487

5467

5446

5426

5606

5586

5565

5545

5525

5505

5485

5464

5444

5424

5604

5584

5563

5543

5523

5503

5483

5462

5442

5422

5602

5582

5561

5541

5521

5501

5481

5460

5440

5420

5600

5580

5559

5539

5519

5499

5479

5458

5438

5418

1.00

1.01

1.02

1.03

1.04

1.05

1.06

1.07

1.08

1.09

0.5416

0.5394

0.5371

0.5349

0.5327

0.5305

0.5282

0.5260

0.5238

0.5215

5414

5391

5369

5347

5325

5303

5280

5258

5235

5213

5412

5389

5367

5345

5322

5300

5278

5255

5233

5211

5409

5387

5365

5344

5320

5298

5276

5253

5231

5209

5407

5385

5362

5340

5318

5296

5273

5251

5229

5206

5405

5383

5360

5338

5316

5293

5271

5249

5229

5204

5403

5380

5358

5336

5313

5291

5269

5247

5224

5202

5400

5378

5356

5333

5311

5289

5267

5244

5222

5200

5398

5376

5354

5331

5309

5287

5264

5242

5219

5297

5396

5374

5351

5329

5307

5284

5262

5240

5217

5295

1.10

1.11

1.12

1.13

1.14

1.15

1.16

1.17

1.18

1.19

0.5193

0.5168

0.5143

0.5118

0.5093

0.5068

0.5042

0.5017

0.4992

0.4967

5190

5165

5140

5115

5090

5065

5040

5015

4990

4965

5188

5163

5137

5113

5088

5062

5037

5012

4987

4962

5185

5160

5135

5110

5085

5060

5035

5010

4985

4960

5183

5158

5132

5108

5083

5057

5032

5007

4982

4957

5180

5155

5130

5105

5080

5055

5030

5005

4980

4955

5178

5153

5127

5103

5078

5052

5027

5002

4977

4952

5175

5150

5125

5100

5075

5050

5025

5000

4975

4950

5173

5148

5122

5098

5073

5047

5022

4997

4972

4947

5170

5145

5120

5095

5070

5045

5020

4995

4970

4945

1.20

1.21

1.22

1.23

1.24

1.25

1.26

1.27

1.28

1.29

0.4942

0.4913

0.4884

0.4855

0.4826

0.4797

0.4768

0.4739

0.4710

0.4681

4939

4910

4881

4852

4823

4794

4765

4736

4707

4678

4936

4907

4878

4849

4820

4791

4762

4733

4704

4675

4933

4904

4875

4846

4817

4788

4759

4730

4701

4672

4930

4901

4872

4843

4814

4785

4756

4727

4698

4669

4928

4899

4870

4841

4812

4783

4754

4725

4696

4667

4925

4896

4867

4838

4809

4780

4751

4722

4693

4664

4922

4893

4864

4835

4808

4777

4748

4719

4690

4661

4919

4890

4861

4832

4803

4774

4745

4718

4687

4658

4916

4887

4858

4829

4800

4771

4742

4713

4684

4655

1.30

1.31

1.32

1.33

1.34

1.35

1.36

1.37

1.38

1.39

0.4652

0.4618

0.4583

0.4549

0.4515

0.4481

0.4446

0.4412

0.4378

0.4343

4649

4614

4580

4546

4511

4477

4443

4408

4374

4340

4645

4611

4577

4542

4508

4474

4439

4405

4371

4336

4642

4607

4573

4539

4505

4470

4436

4402

4367

4333

4638

4604

4570

4535

4501

4467

4432

4398

4364

4330

4635

4601

4566

4532

4498

4463

4429

4395

4360

4326

4631

4597

4563

4529

4494

4460

4426

4391

4357

4323

4628

4594

4559

4525

4491

4457

4422

4388

4354

4319

4625

4590

4556

4522

4487

4453

4419

4384

4350

4316

4621

4586

4553

4518

4484

4450

4415

4381

4347

4312

1.40

1.41

1.42

1.43

1.44

1.45

1.46

1.47

1.48

1.49

0.4309

0.4267

0.4225

0.4183

0.4141

0.4099

0.4056

0.4014

0.3972

0.3930

4305

4263

4221

4178

4136

4094

4052

4010

3968

3926

4301

4258

4216

4174

4132

4090

4048

4005

3964

3921

4296

4254

4212

4170

4128

4086

4044

4001

3959

3917

4292

4250

4208

4166

4124

4082

4040

3997

3955

3913

4288

4246

4204

4162

4120

4077

4035

3993

3951

3909

4284

4242

4200

4157

4115

4073

4031

3989

3947

3905

4280

4237

4195

4153

4111

4069

4027

3985

3943

3900

4275

4233

4191

4149

4107

4065

4023

3980

3938

3896

4271

4229

4187

4145

4103

4061

4018

3976

3934

3892

1.50

1.51

1.52

1.53

1.54

1.55

1.56

1.57

1.58

1.59

0.3888

0.3840

0.3791

0.3740

0.3688

0.3635

0.3580

0.3523

0.3465

0.3405

3883

3835

3786

3735

3683

3630

3574

3517

3459

3399

3878

3830

3781

3730

3677

3624

3569

3511

3453

3393

3874

3825

3778

3724

3672

3619

3563

3506

3447

3386

3869

3820

3771

3719

3667

3613

3557

3500

3441

3380

3864

3818

3766

3714

3662

3608

3552

3494

3435

3374

3859

3811

3760

3709

3656

3602

3546

3488

3429

3368

3854

3808

3755

3704

3651

3597

3540

3482

3423

3362

3850

3801

3750

3698

3646

3591

3534

3477

3417

3355

3845

3796

3745

3693

3640

3586

3528

3471

3411

3349

IS: 3043 Alternative Method

IS:3043 Alternative method Procedure

Two suitable direction at 90 degree apart at one corner of the fence are first selected.

The potential electrode and current electrode are placed in these direction 250 to 300 meters away from the fence at the same distance.

A reading is taken under these conditions.

The current electrode is then moved in 30m steps until the same readings are obtained for three consecutive locations.

This procedure is termed as locating the remote current electrode distance.

Case Study

Positioning of Current electrode

The current electrode is then left in the last foregoing position and the potential electrode is moved out in 30m. Step until three consecutive reading are obtained without a change in value. The last reading then corresponds to the true value of earth resistance

Sl No. Spacing In Meters

P2

Spacing In Meters

C2

Earth Tester Reading(Ω)

1 270 270 0.026

2 270 300 0.039

3 270 330 0.039

4 270 360 0.039

Case Study

Positioning of Potential electrode

Resistance of the Grounding System = 0.040Ω i.e. 40 milliohms.

Sl No. Spacing In Meters

P2

Spacing In Meters

C2

Earth Tester Reading(Ω)

1 270 360 0.039

2 300 360 0.040

3 330 360 0.040

4 360 360 0.040

Interval of Measurement

IS: 3043: 1987. Clause 34.42 (page76): Normally annual measurement of earth resistance of substations shall be carried out but local circumstances in the light of experience may justify increase or decrease in this interval but it should not be less than once in two years. This shall be compared with the internal record.

Although resistance to ground will change seasonally and over time any increase of the resistance > 20% or more should be investigated and corrective action taken to lower the resistance.

Case Study comparing All three methods

Distance between station earth (P1C1) and potential electrode (P2) mtrs

Earthing tester reading Ω

Earth Pit No 1 Earth Pit No:2 Earth Pit No3

3 5.59 4.46 14.92

6(20% R1) 7.04 5.00 16.12

9 7.64 5.43 16.68

12(40%R2) 8.06 5.77 17.09

15 8.34 6.10 17.19

18(60%R3) 8.69 6.40 17.37

18.54(61.8%of30) 8.78 6.47 17.40

21 9.00 6.73 17.60

24 10.08 7.02 17.93

27 11.14 7.84 18.56

Remote Electrode(C2) from station

ground (C1P1) 30m 30m

30m

Distance between station earth (P1C1) and potential electrode (P2) mtrs

Earthing tester reading Ω

Fall of Potential Method

Ave. Of

8.06+8.34+8.78+

9.00= 8.545

Ave. Of 5.43+5.77+

6.10+6.40+

6.73+7.02

=6.242

Average of

17.09+17.19+17.3

7

+17.60=17.46

8.545 6.242 17.46

E.B Curd’s Method 8.78 6.47 17.40

Slope Method µ= (R3-R2)

(R2-R1)

(R3-R2)

(R2-R1)

(R3-R2)

(R2-R1)

8.69-8.06

8.06-7.04

6.40-5.77

5.77-5.00

17.37-17.09

17.09-16.12

0.69

1.02

0.63

0.77

0.28

0.97

0.6765 0.8102 0.28

From the chart Value = 0.6013 0.5785 -

Remote electrode (RE)30m = 60.13% of RE(30) 57.85% of RE(30) -

18.039m 17.355m

Value = 8.69Ω 6.40Ω

Results

Analysis of Results

Method Earth pit 1 Earth pit 2 Earth pit 3

Fall of Potential 8.545Ω 6.242Ω 17.46Ω

E.B Curd’ts 8.780Ω 6.470Ω 17.40Ω

Slope Method 8.690Ω 6.400Ω -

Remote electrode (C2) at 30 mtr from earth pit (C1P1). Earth Pits are conventional type back filled 2Ft all around the electrodes. Earth Pit No1: Located at A & B colony 50mm dia 3mtrs Long GI Pipe. Earth Pit No2: Located in 33KV Substation 100mm dia 3mts Long GI Pipe. Earth Pit No3: Near DG Set New 60mm dia 2mtrs Long GI pipe.

Calculation of Earth resistance of Multiple Electrodes

Multiple electrodes in parallel yield lower resistance to ground than a single electrode.

Multiple rods are commonly used to provide the low grounding resistance required by high capacity installations.

Adding a second rod does not however provide a total resistance of half that of a single rod, unless the two are several rod length apart.

A useful rule is that grounding systems of 2-24 rods placed one rod length apart in a line, hollow triangle, circle or square will provide a grounding resistance divided by number of rods and multiplied by the factor F

Multiplication Factor For Multiple Rods

No. of Rods F

2 1.16

3 1.29

4 1.36

8 1.68

12 1.80

16 1.92

20 2.00

24 2.16

Calculation of ground resistance of pipe / rod for various

length and dia (Asper IS 3043 : 1987 ) Leng

th (a) (b) © (d) (e) (f) (g) (h) (i) (j)

in

Mtrs 100 ρ

d=40

mm

d=50

mm

d=80

mm d=126mm a x b a x c a x d a x e

%

change

2ΠL

log 4L /

d

log 4L /

d

log 4L /

d log 4L / d R in Ohms

R in

Ohms

R in

Ohms

R in

Ohms b & d

1 15.9155 4.6052 4.3820 3.9120 3.4578 73.2941 69.7417 62.2614 55.0326 15.05

2 07.9578 5.2983 5.0752 4.6052 4.1509 42.1628 40.3874 36.6473 33.032 13.08

3 05.3052 5.7038 5.4806 5.0106 4.5564 30.2598 29.0757 26.5822 24.1726 12.15

4 03.9789 5.9915 5.7683 5.2983 4.8441 23.8396 22.9515 21.0814 19.2742 11.57

5 03.1831 6.2146 5.9915 5.5215 5.0672 19.7817 19.0715 17.5755 16.1294 11.15

6 02.6526 6.3969 6.1738 5.7038 5.2495 16.9684 16.3766 15.1299 13.9248 10.83

7 02.2736 6.5511 6.3279 5.8579 5.4037 14.8946 14.3871 13.3185 12.2859 10.58

8 01.9894 6.6846 6.4615 5.9915 5.5372 13.2983 12.8545 11.9195 11.0157 10.37

9 01.7684 6.8024 6.5793 6.1092 5.6550 12.0294 11.6348 10.8035 10.0003 10.19

10 01.5915 6.9078 6.6846 6.2146 5.7604 10.9938 10.6385 09.8905 09.1677 10.04

11 01.4469 7.0031 6.7799 6.3099 5.8557 10.1328 09.8098 09.1298 08.4726 09.90

12 01.3263 7.0901 6.8669 6.3969 5.9427 09.4036 09.1076 08.4842 07.8818 08.50

Note

Calculations are based on uniform Soli resistivity of 100 Ohm Mtrs.

Ground resistance of pipe / rod as per clause 9.2.2 of IS 3043 : 1987 (Reaffirmed 2001) Code of practice for earthing

Since ground resistance is directly proportional to the soil resistivity, for any other soil resistivity, the above value shall be multiplied

Calculation of ground resistance of pipe / rod for various length and diameter as per IEEE STD 80 : 2000

Length (a) (b) © (d) (e) (f) (g) (h)

in Mtrs. 100 ρ d=40 mm d=50 mm d=80 mm a x b a x c a x d % change

2ΠL log (8L / d) - 1 R in Ohms R in Ohms R in Ohms b & d

1 15.9155 4.2983 4.0752 3.6052 68.4096 64.8588 57.3786 16.12

2 07.9578 4.9915 4.7683 4.2983 39.7214 37.9452 34.2050 13.89

3 05.3052 5.3969 5.1738 4.7038 28.6316 27.4480 24.9546 12.84

4 03.9789 5.6846 5.4615 4.9915 22.6185 21.7308 19.8607 12.19

5 03.1831 5.9078 5.6846 5.2146 18.8051 18.0947 16.5986 11.73

6 02.6526 6.0901 5.8670 5.3969 16.1546 15.5628 14.3158 11.38

7 02.2736 6.2442 6.0211 5.5511 14.1968 13.6896 12.6210 11.10

8 01.9894 6.3778 6.1546 5.6846 12.6880 12.2440 11.3090 10.87

9 01.7684 6.4955 6.2724 5.8024 11.4866 11.0921 10.2610 10.67

10 01.5915 6.6001 6.3778 5.9078 10.5041 10.1503 09.4023 10.49

11 01.4469 6.6962 6.4731 6.0031 09.6887 09.3660 08.6859 10.35

12 01.3263 6.7832 6.5601 6.0901 08.9966 08.7007 08.0773 10.22

Note

Calculation based on ρ (uniform soil resistivity) = 100 ohm mtr

Ground resistance of pipe / rod as per clause 13.3 of IEEE STD 80: 2000 AC Substation Grounding

Since ground resistance is directly proportional to the soil resistivity, for any other soil resistivity, the above value shall be multiplied

Current Carrying Capacity of Earth Electrode

Current caring capacity of an earth electrode depends on the total surface area of the electrode in contact with earth, resistivity of the soil and duration of fault in seconds

The formula for current caring capacity (Current density) is:

Current density = 7.57 X 10³ Amp / Sq-m

√ρt

ρ = Resistivity of the soil (assumed uniform) in ohm-m.

t = Duration of fault in seconds.

Geometry & Number of Electrodes required

The total surface area coming in contact with earth is the criteria. To calculate the number of earth electrodes required for any

particular application depends on the fault level. The calculation is as follows:

Calculation of No.of Plates required: For Example: The total surface area = 0.6 x 0.6 x 2 sq.m = 0.72 sq.m Fault current = 6 kilo amperes Duration of Fault = 1 sec. Soil Resistivity = 100 ohm - m Current density = 7.57 X 10³ Amp / Sq-m

√ρt = 7.57 X 10³ = 757 Amp /Sq-m √100X1 One Plate will carry 757 X 0.72 = 545.04 Amperes

Geometry & Number of Electrodes required

To carry 6 kilo amperes, No.of plates required = 6000 / 545.04 = 11 Nos.

Calculation of No.of Pipes required: For Example: The total surface area of a 3 mtr long 80 mm dia = π x 0.08 x 3 sq.m = 0.754 sq.m Fault current = 6 kilo amperes Duration of Fault = 1 sec. Soil Resisitivity = 100 ohm - m Current density = 7.57 X 10³ Amp / Sq-m

√ρt = 7.57 X 10³ = 757 Amp /Sq-m √100X1 One Pipe will carry 757 X 0.754 = 570.778 Amperes To carry 6 kilo amperes No.of plates required = 6000 / 570.8 = 10.5 = 11 nos

Note: The total surface area of one pipe electrode of 80 mm dia, 3 mtr long is more

than one plate electrode of 0.6 mtr X 0.6 mtr

Conductor Sizing

The fast acting circuit breakers operates in 0.2 secs and the fault clearing time of back up protection system ensures greater safety margin of 0.5 secs. In general for safety 1 sec duration is considered in India. The current caring capacity of the material is as follows:

Conducting

Material

Current rating 1

sec

Current rating

3 secs

Copper 205 amp / mm2 118 amp / mm2

Aluminium 126 amp / mm2 073 amp / mm2

Iron (GI) 080 amp / mm2 046 amp / mm2

For any other duration rating is: 1 sec rating amperes. √t Where t = Duration of fault in secs.

Maximum Accepted Earth Resistance

•References •US AID INDIA Book

•Page 92 – Modernisation of power distributions

• The earth resistance shall be as low as possible and shall not exceed the following limits •Power stations (generating station) 0.5 ohms •EHT Sub-station 1.0 ohms •33 KV Stations 2.0 ohms •DT(Distribution Transformer) Structure 5.0 ohms

•Tower Foot resistance 10.0 ohms

Maximum Accepted Earth Resistance

IEEE standard 142-2007 chapter 4 page 164 – Resistance in the 1 ohm to 5 ohms range are generally found suitable for industrial plant sub-station and buildings and large commercial installations.

Lightning arrestors ground resistance for protection of buildings and allied structures – Less than 10 ohms …… Clause 12.3.1 Page 32 IS 2309 : 1989. Clause 9.4.3 of BS 7430:1998.

Guide for control of Undesirable Static Electricity: Earthing Resistance for the control of static electricity : Less than 10 ohms. Table 4 page 28 of IS 2689:1989 ( Reaffirmed March 2010)

Requirement of an Embedding Material

It should have high electrical conductivity which should be constant, unaffected by changes in temperature & moisture;

It should permanently remain once embedded and should not be either dissolved in or swept away by water

It should have high swelling property to absorb water and retain the same over long periods of time

It should not cause or accelerate the corrosion of the ground electrode material, such as steel

It should be easily applicable

It should not cost much in relation to the total cost of grounding installation.

Embedding Material : Bentonite

One of the most suitable substances for chemical treatment of soils which fulfills most of the above requirements is a clay known as Bentonite.

Bentonite

Calcium based Sodium Based

Bentonite Properties

Bentonite contains Na o (Soda), K o (Potash), Cao (Lime), Mgo (Magnesia) & other mineral salt that ionize forming a strong electrolyte with :

a) pH : 8-10

b) ρ : 2.5 Ohm-m at 300 % moisture

c) Swell index by volume : ≥ 8

d) Quantity required for Pipe electrode as per

IS:3043-1987 (2.75 m long 100mm Id 13 mm thick) : 45 Kg

Suppliers of Bentonite

M/s Amar minerals Pvt Ltd., Netivali Baug, Kalyan Dist.Thane, Maharastra

M/s Amarjyot Industries No.45, Dr.Meisheri Road,Near Sandhurst road,Railway Stn.Bombay Works:A-108, MIDC, Dombivili, Dist.Thana

M/s Industrial Minerals & Chemicals Co.Pvt Ltd., No.125, Narayan Dhauru street, Nagaevi, Bombay – 400 003 Works: Kurla Road, chakala Andheri Bombay-58 Works: Chinchpokli cross lane, Bomaby 400 027

M/s International Minerals & Chemicals Co. No.54-D, Govt.Industrial Estate,Bombay-400 067


M/s Ambika Minechem Industries No.129/131, Kazi Sayed street 4th Floor, Bombay – 400 003

M/s Mysore Agencies 23/1, 3 rd Cross, Lalbaugh Road, Bangalore – 560 027

M/s Baroda Mineral Grinding Industries National highway, Naroda Ahmedabad

M/s J.D.Jones & Co.Pvt Ltd., C/5, Gillander House, No.8, Netaji Subhash Road, Calcutta 700001

M/s Metamine Industries Rathnagarmata Road, Kapadvanj, Dist.Kaira Gujarat


M/s Somanath Minerals & Chemicals No.72, Chitra Industrial Estate,Bhavnagar 364 004 (Gujarath)

M/s . Sunders India Corporation Near Indian Airlines Corporation, Diwanpara Road, Bhavnagar – 364 001

M/s. Manjunatha Pulverisers Sabuvani Buildings, N.R.Road, Bangalore – 560 002

M/s. Mysore City & Mineral Industries No.1032, IV Block, Rajaji nagar, Bangalore 560 010

M/s. Mine Chemical Industries, Peenya Industrial Estate,Phase III, Bangalore

M/s. Binto Plast Pvt Ltd., Industrial Estate, Jodhpur – 342 001

M/s.United Engineering Corporation APSRTC Complex,Vishakapatnam

M/s. Ashapura Group of Industries “ VIBHA” 55/3 13th H Main, HAL 2nd Stage Indira nagar,Bangalore – 560 008 H.O.81/82, Mittal Court C, Nariman point, Bombay – 400 021


M/s . OSWAL MINERALS No.6, 2nd Main Road,Rama chandrapuram ,Bangalore – 560 021,Ph: 080- 23123187

M/s. KUTCH MINERALS H.K Road, Kachh – Mandvi,Gujarat – 3704650,Email: [email protected],Ph: 02834- 223009 / 223012

M/s. Gujarat Clay Mills Pvt. Ltd Gujarat Clay Mills Compound,Phoenix Hyundai, 1st Floor, Opp Buntara Bhavan,Buntara Bhavan Marg, Kurla (E) Mumbai – 70,Ph: 022- 24052329 ,Fax: 022- 24053357

M/s. National Mineraly Development Corporation Ltd( A Govt. of India Enterprises) Khanij Bhavan 10- 3 -311/A, Castle Mills, Masab Tank Hyderabad – 28 Ph: 040- 23538713 Fax: 040 – 23538711

M/s. S.D Fine – Chem Ltd 315- 317, TVI EST. 248 Worli Road, Mumbai – 400 030 Ph: 022- 4949006 Fax: 022- 24937232

Suppliers of Earth Testers

Megger M/s . Josts Engineering Company Ltd 1/3, Krishna Vilas Palace Road, Bangalore – 560001 Ph: 22263707 Contact Person: Mr. Raghavendra Mob: 9448374211 FLUKE M/s.TTL Technologies Pvt Ltd 3071, 10th Cross, 11th Mani, HAL 2nd Stage, Bangalore – 560008 Ph: 080- 25260646, 25251859

Suppliers of Earth Testers

CHAUVIN AROUX M/s. Cyronics Instruments Pvt Ltd 001 Ground Floor Pooja Apts. V R Bhide Marg Dadar(W) Mumbai – 400 028 Contact Person: Mr. Rahul More Cell No: 9860093203 KYORITSU M/s. Messals Overseas ( India ) Pvt Ltd C-5, Shakti Nagar, Tonk Road, Jaipur – 302 018 Ph: 91-141-2705361 Contact Person: Mr. Aviral Sharma Mob: 9799559319

Thanks!

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