A New Artificial Treatment for the Reduction of Resistance in Ground Electrode

IEEE TRANSACTIONS ON POWER DELIVERY, VOL. 19, NO. 2, APRIL 2004 601

A New Artificial Treatment for the Reductionof Resistance in Ground Electrode

Hugo E. Martínez, Edward L. Fuentealba, Luis A. Cisternas, Hector R. Galleguillos, Jorge F. Kasaneva, andOsvaldo A. de la Fuente

Abstract—This study describes a resistance reduction additive(RRA) for reducing and maintaining reduced resistance of groundelectrodes over time. The RRA employed was a mixture of inor-ganic salts, some of which occur as residues from industrial min-eral processing in Chile. Chemical characteristics of the mixtureare described, as well as results of measurements of electrical resis-tance of ground electrodes over time with and without RRA treat-ment. Measures are also given for current intensities and loss ofelectrode mass in test electrodes buried below ground with RRAand within cell containers having a specific capacity. Small scaletests were made on the effects of impulse current in test cells con-taining electrodes treated with the RRA.

Index Terms—Chemical analysis, corrosion, grounding,grounding electrodes, resistance measurement.

I. INTRODUCTION

THE objectives that are pursued in the construction of agrounding system are several, and they obey different

reasons. The most important thing is to guarantee the peoplesecurity. However, to ensure good operation of the electric andelectronic system is also of great importance [1], [2]. Fromthe point of view of security, a grounding system must preventpeople from being subjected to dangerous electrical potentialdifferences [1]–[4]. Now, from the point of view of a goodoperation in an electric and electronic system, the groundingsystems must complete high-priority functions, as shown in thefollowing [1]:

• stable tensions between active phases and grounding,when a single-phase fault takes place in a power electricsystem;

• in the event of fault to ground, to provide a low impedanceroute;

• in the event of atmospheric discharges, to drive this greatenergy to ground;

• establishment of a voltage reference level.

Manuscript received September 24, 2002. This work was supported underProject PROIM “Industrial Minerals: New Opportunities for development ofthe country,” University of Antofagasta–Chile.

H. E. Martínez and E. L. Fuentealba are with the Department of Elec-trical Engineering, University of Antofagasta, Antofagasta, Chile (e-mail:[email protected]; [email protected]).

L. A. Cisternas and H. R. Galleguillos are with the Department of Chem-ical Engineering, University of Antofagasta, Antofagasta, Chile (e-mail: [email protected]; [email protected]).

J. F. Kasaneva is with the Physics Department, University of Antofagasta,Antofagasta, Chile (e-mail: [email protected]).

O. A. de la Fuente is with the Department of System Engineering, Universityof Antofagasta, Antofagasta, Chile (e-mail: [email protected]).

Digital Object Identifier 10.1109/TPWRD.2004.824760

There exist cases where the high resistivity of soil makes it dif-ficult or even impossible to obtain low resistance values in theconstruction of a ground electrode. For this reason, there are, atpresent, natural and artificial means of modifying soils whichcover ground electrodes which have low resistance characteris-tics. These include changing the nature of the overlying soil [1]and covering it with natural materials, such as bentonite [5], orartificial compounds, such as synthetic resins.

This report presents results of values from test-scale groundelectrodes with and without the application of current whichhave been treated with a resistance reduction additive (RRA)composed of raw materials and residual inorganic salts fromChile. Test times ranged over periods somewhat over one year.Although the result shown in this work only contains data be-tween one or two years, similar results have observed for othertests for time period of over four years. Both tests, with andwithout application of current, were carried out at four locationsincluding Antofagasta, Rancagua, Chuquicamata, Maria Elenanitrate deposit, and the town of Mejillones. Results are also pre-sented on voltages and lightning current discharges in cells ofspecific dimensions containing a hemispherical electrode cov-ered with the test material mentioned above for the reduction ofresistance in ground electrode.

II. CHEMICAL CHARACTERIZATION OF THE TEST PRODUCT

The RRA used was the product of combining three types ofmixtures of inorganic salts, which are here termed MA, MB,and MC, respectively. The following results were obtained inanalysis of each of these mixtures by X-ray diffraction usinga Siemens Co. model D5000 automatic computerized X-raydiffractometer.

The mixture MA was composed primarily of halite (NaCl),and in lesser proportions of bloedite [Na Mg SO H O] andstevensite [montmorillonite group Ca Mg Si O OHH O].The mixture MB was primarily halite and montmoril-

lonite [Na Al Mg Si O OH nH O]. Its minorcompounds included huntite [Mg Ca CO ], ankerite[Ca Fe Mg CO ], and calcite (CaCO ).

Inorganic salt mixture MC was composed primarilyof halite, with minor fractions including gismondine(CaAl Si O H O), ankerite, diaspora, hanskite[Kna CO SO Cl], Montmorillonite, and saponite[Mg Si Al O OH H O].

Following X-ray diffraction analysis of qualitative compo-sition, quantitative evaluation was done for some of the moreimportant elements and compounds present in the salt mixtures.

0885-8977/04$20.00 © 2004 IEEE

602 IEEE TRANSACTIONS ON POWER DELIVERY, VOL. 19, NO. 2, APRIL 2004

TABLE ICHEMICAL ANALYSIS OF INORGANIC MIXTURES

TABLE IIMEASUREMENT OF ACIDITY IN THE RRA

TABLE IIIMEASURES OF RESISTIVITY IN THE CELL

Results of chemical analyses are listed in Table I. Determina-tion of cations was made using atomic absorption spectroscopy(AA) using a Varian Co. Model 220FS instrument. Chloridesand carbonates were analyzed volumetrically and sulfates bygravimetry.

Elemental analyses were converted to compositions byminerological substance using the “Minerology Module” ofHSC Chemistry for Windows software [8]. The results are a“best estimate,” given that several solutions to the problemexist. The proximate composition of mixture MA was 70%halite, 26% bloedite, and 4% stevensite. The MB mixturecontained about 85% gismondine, 12% ankerite, and 3% halite,and the MC mixture was about 64% huntite, 35% halite, and1% montmorillonite.

Table II compares the results of pH measurement [6], [7] ona specific quantity of the RRA with that of a soil sample fromthe II Region. This measurement is also given for three differentweights of RRA (1, 2, and 3 g) in a constant volume of distilledwater.

Determination of resistivity of the RRA was done in acell measuring 10 10 10 cm, containing copper-plateelectrodes. Results of the resistivity tests are given in Table III.

Based on the average resistivity results from above, a valuewas obtained of 0.22 - . A comparable result reported in [7]was 0.23 - at 23 C.

It is important to indicate that the resistivity value can be fur-ther lowered by altering the proportions of raw materials andsalts in the composition of the RRA described above.

Fig. 1. Placement of test electrodes in soils of the University of Antofagasta.

III. TESTS OF ELECTRODES WITHOUT APPLICATION

OF CURRENT

Test electrodes consisted of copper rods (pikes) 1 m in lengthand 5/8 inches in diameter. These were buried horizontally in aditch about 0.5 m wide and 0.6 m deep, where tests were carriedout without injection or circulation of current.

A. II Region, Antofagasta

After having carried out various tests during 1997 [2], [3]and carrying out definitive determinations on the proportionsof elements which formed the RRA, six test electrodes wereinstalled on the terrain of the University of Antofagasta, wheresoil resistivity was about 3000 -m . Electrodes were installedabout 4 m apart.

Fig. 1 presents a schematic diagram of the positions of the sixsample electrodes.

Sample RA was an electrode installed directly in the soil withno RRA. Sample RB was an electrode improved using a re-sistance reduction additive sold widely in the electrotechnicalmarket, treated with 25 l of tap water. Samples RC, RD, and REwere electrodes to which had been added 7, 14, and 21 kg of theRRA described above, treated, respectively, with 25, 50, and 60l of tap water. Sample RF was a test electrode which receiveda single application of 14 kg of the RRA over 20 cm of earthwhich covered it and was then treated with 25 l of tap water.The resistance of the tap water is 10,4 -m

Fig. 2 shows the comparative values of resistance in the sixground electrodes as a function of time.

Fig. 3 presents graphs of Fig. 2, reducing the scale of theground resistances of the ground electrodes in order to betteremphasize the development of resistance over time in the testelectrodes of the experimental ground electrodes which wereartificially enhanced with RRA. It can be seen that the groundelectrode with the least resistance was that having the largestquantity of RRA (RE), followed in descending order by RD andRC, and that the values remained practically fixed over time.

B. VI Region, Rancagua

Similar testing was carried out in Chile’s VI Region, wherethe soils are of an agricultural type. The sites measured were lo-cated near the towns of Malloa and Rengo. In Malloa, a 1.5-mrod (pike) 5/8 inches in diameter was installed, the resistance ofwhich (unimproved) was about 43 . This was improved artifi-cially by the addition of 7 kg (RC) of RRA. The test electrodeplaced at Rengo had a resistance of 383 prior to improvement.It was treated with 14 kg (RD) of RRA. This test region was af-fected by unusual climatic conditions during the experimental

MARTÍNEZ et al.: A NEW ARTIFICIAL TREATMENT FOR THE REDUCTION OF RESISTANCE IN GROUND ELECTRODE 603

Fig. 2. Resistances of six ground electrode test electrodes without currentcirculation.

Fig. 3. Enlargement of Fig. 5.

period (May–October 2000), experiencing extreme drought fol-lowed by extreme rains.

Table IV lists the results obtained with the preceding groundelectrodes, carried out by personnel of Electric Company of theCompañia General de Electricidad (CGE). It is important tostate here that these results confirmed that RRA was insoluble.

Fig. 4 shows the graphs of ground electrodes as a function oftime, from Table IV. According to the results obtained in the VIRegion of Chile, there was a decrease in resistance to groundwith an increase in the quantity of RRA.

C. II Region, Chuquicamata, Maria Elena, and Mejillones

Three test electrodes were installed, using 14 kg (RD) ofRRA. The resistance in the ground electrode without applica-tion of current in Chuquicamata, Maria Elena, and Mejillonesis shown in Figs. 5–7.

Fig. 4. Measures of resistance in ground electrodes in Region VI, Chile.

Fig. 5. Resistance of a ground electrode without current circulation atChuquicamata.

TABLE IVMEASURES OF RESISTANCE IN GROUND ELECTRODES IN REGION VI, CHILE

IV. TEST USING CIRCULATION OF RESIDUAL CURRENT

Sets of three test electrodes were installed as described above,using 14 kg (RD) of RRA, at each of two mining centers innorthern Chile, II Region. One set was installed at the Chuquica-mata copper mine and another at the Maria Elena nitrate de-posits. A third set was installed at the port of Mejillones. Lowlevels of current were applied to each of these electrodes througha dimmer switch (domestic lighting type) to simulate a residualcurrent. Electrodes were recovered at 4-mo intervals in order


Fig. 6. Resistance of a ground electrode without current circulation at MariaElena.

to determine the loss of mass of the electrodes due to corro-sion. This procedure was also carried out on three electrodes atthe University of Antofagasta using the above methods with 7,14, and 21 kg of RRA (RC, RD, and RE) , plus low-level fixedcurrent.

It should be noted that the Chuquicamata and Maria Elenasites are located in the Atacama desert which is exceedingly dryand has intense solar radiation.

The schematic diagram presented in Fig. 8 shows the circuitused to circulate the electric current in each of the groundingtest systems. The measure of the resistance, in agreement withFig. 8, is made through the quotient among the voltage, re-garding the neutral, of the current feed and the current at thebeginning of the electrode.

A. Chuquicamata

Fig. 9 shows the variation in resistances of the groundelectrode of the three electrodes placed at the interior of theChuquicamata mine. Sample R3CC showed high values forresistance as the RRA had been incorrectly placed at initiation.However, the remaining two electrodes increased in valueresistance about 6 mo after installation. In order to determinethe effect of adding water, on November 10, 2000, samples 1and 2 were treated with 40 l tap water. It was observed (withsurprise) that in sample 1, the resistance decreased from 3194to 102 over a period of 15 min and remained at this levelfor over two weeks. Sample 2 did not respond as quickly, butover a period of two weeks, the ground resistance decreasedfrom 7307 to 9.6 . Fig. 10 shows the curves from Fig. 9with a reduced scale on the resistance axis. The test electroderecovered for mass determination (R3CC) which initiallyweighed 1132.58 g, weighed 1130.98 g after 4 mo, suggestingthe loss of 0.4 g of the electrode mass per month.

Fig. 7. Resistance of a ground electrode without current circulation atMejillones.

Fig. 8. Scheme of introduction of ground current to test electrodes.

Fig. 9. Resistance of a ground electrode with current circulation atChuquicamata.



Fig. 11. Variation in resistances of ground electrodes at Maria Elena.

B. Maria Elena

Variation in resistance of the ground electrodes for three elec-trodes installed at the Maria Elena nitrate deposits is shown inFig. 11. Sample R3CC from this site had also been incorrectlyinstalled, resulting in a high resistance value compared to theother two electrodes. Fig. 12 shows the development of resis-tance over time of the ground electrodes. The electrode recov-ered was R3CC; at installation, its weight was 1211.34 g, andafter 4 mo, its weight was 1119.40 g, suggesting a loss of massof 22.98 g/mo. This value, as the result for Chuquicamata, canbe considered low. A linear approximation gives 100 years tocomplete mass lost.


Fig. 13. Current in three electrodes installed in soils of the University ofAntofagasta.

C. Antofagasta

In Figs. 13 and 14, the results of magnitudes of intensitiesof current and resistance of ground electrodes consisting of thethree electrodes with RRA treatments (7, 14, and 21 kg) areshown installed on the terrain of the University of Antofagasta,similar to RC, RD, and RE of Fig. 1. The installation date wasAugust 31, 1999.

D. Mejillones

Fig. 15 shows the variations in the resistance of ground elec-trodes consisting of three electrodes placed at the Mejillonessubstation of the EDELNOR electric company. Sample R3CCfrom this site had also been incorrectly installed, explaining its


Fig. 14. Resistances of ground electrodes in three electrodes in soils of theUniversity of Antofagasta treated with 7, 14, and 21 kg of RRA.

Fig. 15. Variation in resistances of ground electrodes at Mejillones.

high value compared to the other two electrodes. The recoveredelectrode from this site was R3CC which, prior to installation,weighed 1120.04 g, and after 4 mo weighed 1117.43 g, sug-gesting a loss of electrode mass of 0.65 g/mo. Fig. 16 showsthe results of waveform tension applied and current circulatedthrough the electrodes at the sites mentioned above.

V. TESTS WITH IMPULSE CURRENT

In this test, the test electrode was in the form of a hemispherewith a radius of 2.51 cm. The hemisphere is placed in a coppercell containing the RRA.

Fig. 17 shows the dimensions of the cell and the placementof the RRA. First, the resistance of the electrode is measured

Fig. 16. Record of voltage waves and current in an electrode of the groundelectrode type treated with RRA.

Fig. 17. Cell used for testing impulse current.

TABLE VRESISTANCE OF THE HEMISPHERICAL ELECTRODE WITH INDUSTRIAL

FREQUENCY VOLTAGE RMS

at a frequency voltage root mean square (rms) of 50 Hz. Theseresults are given in Table V. Subsequently, the average resis-tance of the electrode measured within the RRA at industrialfrequency voltage was about 1.35 .

Tests were later carried out with impulse current of 50/200 ,with negative polarity on the ground electrode described above.The results are shown in Table VI.

Fig. 18 shows one of the records of voltage and current inthe tests carried out at the High Voltage Laboratory of the


TABLE VIIMPULSE TESTS

Fig. 18. Record of voltage and current in impulse test.

Department of Electrical Engineering of the University ofChile, Santiago.

Results in Table VI suggest that the was the mostrepresentative value, which showed a final averaged value of0.89 .

VI. CONCLUSION

• A resistance reduction additive (RRA) was developedfrom natural resources and inorganic salt residues ob-tained from mining activity in the Antofagasta Regionof Chile, which allowed reduction of resistance andextended the life of electrical ground electrodes.

• The RRA developed for the ground electrodes was nothighly corrosive, as ground electrodes treated with the ad-ditive showed a less than 1 g of loss in mass per monthwithout the presence of circulating current.

• This additive is recommended for use in ground electrodesin both neutral ground or service soils based on observa-tions that in ground electrodes maintained with circulatingcurrent for periods of over a year, there was rapid responsein lowering their resistance upon treating them with water.

• In insulating soils in protection ground also without circu-lating currents, the RRA maintained its resistance valuefor periods greater than a year without the addition ofwater.

• The product developed showed 34% less resistance to im-pulse current (out standard) with respect to the industrialfrequency voltage.

ACKNOWLEDGMENT

The authors thank the High Voltage Laboratory of theDepartment of Electrical Engineering of the Universidadde Chile. They also thank Codelco Chile Chuquicamata,EDELNOR Electric Company, SQM Chemical Company, andCGE Electrical Company.

REFERENCES

[1] A. Barachini, “Tratamiento de los electrodos para tomas de tierra porintermedio de procedimientos artificiales,” Revista Electrotécnica Ar-gentina, Jan./Feb. 1982.

[2] H. Martínez, “Nuevo procedimiento que reduce artificialmente laresistencia de las puestas a tierra en suelos de alta resistividad,” in IConferencia Internacional del Área Andina del IEEE, Isla Margarita,Venezuela, Sept. 8–10, 1999.

[3] , “Tratamiento alternativo artificial que reduce y mantiene las re-sistencias de puesta a tierra de suelos con alta resistividad,” in Proc.XIII Congreso Chileno de Ingeniería Eléctrica, Universidad de Santiago,Chile, Nov. 8–12, 1999.

[4] P. Ortuondo and S. Navarro, “Métodos para mejoramiento de puesta atierra en terrenos de alta resistividad,” Endesa Chile, Revista Electrotéc-nica Argentina, 1976.

[5] W. R. Jones, “Bentonite rods assure ground rod installation in problemsoil,” IEEE Trans. Power App. Syst., vol. PAS-99, pp. 1343–1346,July/Aug. 1980.

[6] “Soil Quality. Determination of pH,” Std., ISO 10 390, 1994.[7] “Soil Quality. Determination of Specific Electrical Conductivity,” Std.,

ISO 111 265, 1994.[8] Outokumpu HSC Chemistry for Windows, Versión 4.0, User’s Guide,

Outokumpu Research Oy, Finland, 1999.

Hugo E. Martinez was born in 1953. He received the B.S. degree in electricalengineering from Technical University of Chile, Santiago, Chile, the M.Sc. de-gree in electrical engineering from the University of Chile, Santiago, Chile, theB.S. degree in electrical engineering from Technical University of Chile, andthe Ph.D. degree in electrical engineering from the Universidad Politécnica ofMadrid, Madrid, Spain.

His research interests include grounding systems and polluted insulators.Dr. Martinez is a member of IEEE Chilean Society and CIGRE.

Edward L. Fuentealba was born in 1972 in Tomé, Chile. He received the B.S.degree in electrical engineering with a minor in industrial engineering from theUniversity of Antofagasta, Antofagasta, Chile.

Currently, he is an Assistant Professor in the Electrical Engineering Depart-ment, University of Antofagasta, Antofagasta, Chile. His current research areais electrical power systems.

Luis A. Cisternas was born in 1961. He received the B.S. degree in chemicalengineering from the Catholic University of the North, Antofagasta, Chile,and the Ph.D. degree in chemical engineering from the University of Wis-consin–Madison.

Currently, he is a Professor in the Chemical Engineering Department, Univer-sity of Antofagasta, Antofagasta, Chile. His current interests areas are processesdesign and industrial minerals applications.

Dr. Cisternas is a member of American Institute of Chemical Engineers(AIChE).

Hector R. Galleguillos was born in 1954 in Pedro de Valdivia, Chile. He re-ceived the B.S. degree in chemical engineering from the Catholic University ofthe North, Antofagasta, Chile, and the Ph.D. degree in chemistry from the Uni-versity of Laguna, Laguna, Spain.

Currently, he is an Associate Professor in the Chemical Engineering Depart-ment, University of Antofagasta, Antofagasta, Chile. He has been involved inresearch on thermodynamic of electrolyte solutions and industrial minerals.

Dr. Galleguillos is a member of Sociedad Iberoamericana de Electroquímica(SIBAE).


Jorge F. Kasaneva was born in 1952. He received the B.S. degree in physicsfrom the University of Barcelona, Barcelona, Spain and the B.S. degree inelectronic engineering from the Catholic University of the North, Antofagasta,Chile, and the Ph.D. degree in physics from the University of Barcelona,Barcelona, Spain, in 1990.

Currently, he is an Associate Professor of physics at the University of Antofa-gasta, Antofagasta, Chile. He has been involved in a research project on materialscience.

Osvaldo A. de la Fuente was born in 1969 in Santiago, Chile. He received theB.S. degree with double majors in industrial engineering and mines engineeringfrom the University of Chile, Santaigo, Chile, in 1994 and 1995, respectively.

Currently, he is an Assistant Professor in the Industrial Engineering De-partment, University of Antofagasta, Antofagasta, Chile. His current researchinterest is minerals economics.

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A New Artificial Treatment for the Reduction of Resistance in Ground Electrode