Measurement of Conductivity and Equivalent Salt Deposit Density of Contaminated Glass Plate

M. A. Salam, Member IEEE, Zia Nadir, Nazar Mohammad, Ali Al Maqrashi, Ahmed Al Kaf, Talal Al Shibli, Badar Al Dhohuri

Department of Electrical and Computer Engineering

College of Engineering

Sultan Qaboos University

PO Box: 33, PC 123, Muscat,

Sultanate of Oman

Fax:+968-513454

Abstract: In this paper, the conductivity and Equivalent Salt Deposit Density (ESDD) of glass plate under contaminated condition has been measured in the laboratory. Different concentrations of salt solutions are used in the experiments. Test results in terms of conductivity and ESDD are plotted versus salt concentration and the relationship between the conductivity and ESDD is examined.

Keywords: Glass plate, tap water, distilled water, salt, ESDD and conductivity.

Introduction

Insulators are exposed to outdoor environment for transmission and distribution of electric power. Different types of contaminations contaminate these insulators. To identify the contamination level of an insulator either ESDD or conductivity is used. Generally, contamination can be classified into three categories; industrial contamination, sea contamination and dust contamination. The sea contaminants arrive simultaneously with moisture and are deposited on the insulator surface by the natural wind. The industrial contaminants like cement dust, fumes, fly ash and other gases increases slowly with time. These contaminants form a conducting layer in the presence of light rain or morning dews and causes to flow the leakage current. The heat will be produced due to this leakage current and creates dry band. If the leakage current increases, arc will be produced along the insulator surface. The arcs merge together and form a single arc, which triggers to surface flashover. Many researchers studied this flashover mechanism either considering conductivity or ESDD. M. A. M. Piah and Ahmed Darus [1] modeled the leakage current in terms of conductivity and other environmental parameters. I. R. Vazquez et al [2] have tested the non-ceramic insulators by non-standard method where they expressed the contamination level by ESDD. M. Farzaneh et al [3] have proposed the dynamic model of dc arc on ice surface by considering the surface conductivity. J. P. Holtzhausen et al [4] have proposed the theoretical model to calculate the flashover voltage of ac energized post type insulator. They used the conductivity for representing the contamination level of the insulator. F. V. Topalis et al [5] studied the critical flashover voltage of the insulator with the variation of surface conductivity and ESDD.

In this paper, ESDD and surface conductivity of different contaminated glass plates have been measured using IEC standard [6].

Measurement Procedure

Only one size of perspex glass plate is chosen for carrying out the experimental work. The size of glass plate is cm. Initially, NaCl with the amounts of 0.2gm, 0.4gm, 0.6gm, 0.8gm and 1.0gm are mixed with tap water to get the solutions. In the experiment tap water is used for comparative study. The glass plate is contaminated by the 0.2gm salt solution and dried in microwave oven. The dry granules of the salt were collected by small brush from the contaminated glass plate and mixed with 200 ml tap water to get the solution for specific area of the glass plate. This process is repeated for other samples of salt solutions. The conductivity of each collected salt solution was measured by the conductivity-measuring instrument. At the same time, temperature is also recorded. The conductivities at different temperatures are converted to 200 temperatures by the expression [6] as,

(1)

where:

is the solution’s temperature,

is the volume conductivity at a temperature , (S/m)

is the volume conductivity at a temperature (S/m)

is the factor depending on the temperature as given in Table 1.

Table 1: Values of at different temperature

5 / 0.03156
10 / 0.02817
20 / 0.02277
30 / 0.01905

The salinity of the solution is determined by the following expression [6] as,

(2)

Finally, the equivalent salt deposit density can be determined by the following expression [6] as,

(3)

where:

is the volume of the solution, cm3

is the area of the cleaned surface, cm2

The measurement results in terms of correction conductivity and ESDD for tap water are shown in Table 2.

Table 2: Conductivity and ESDD of a cm contaminated glass plate.

Solution
(gm/ml) /
(S/cm) / ESDD
(mg/cm2)
0.2 / 0.019113 / 0.050967
0.4 / 0.023823 / 0.063948
0.6 / 0.033100 / 0.089731
0.8 / 0.043332 / 0.118422
1.0 / 0.047546 / 0.130301

Again, the amount of salt is varied as 0.1gm, 0.3gm, 0.5gm, 0.7gm and 0.9gm and mixed with 200ml tap water to get different salt solutions. Same procedure is repeated to measure the correction conductivity and ESDD of the cm size contaminated glass plate. The measured results in terms of correction conductivity and ESDD are shown in Table 2.

Table 2: Conductivity and ESDD of a cm contaminated glass plate.

Solution
(gm/ml) /
(S/m) / ESDD
(mg/cm2)
0.1 / 0.01562 / 0.041401
0.3 / 0.021562 / 0.057706
0.5 / 0.024663 / 0.066272
0.7 / 0.039284 / 0.107044
0.9 / 0.045647 / 0.124944

Results and Discussion

The correction conductivity and ESDD are measured by using glass plate and different amount of salt concentration. The NaCl and tap water is used as artificial pollution. The correction conductivity and ESDD obtained from present measurements by varying the amount of salt concentration is presented in Figure 1 and Figure 3.

The correction conductivity and corresponding ESDD for cm size glass plate varies with the variation of salt concentration as shown in Fig. 1. As in Fig.1, the salt concentration from 0.2 gm to 0.8 gm, the variation of conductivity and ESDD is almost linear. The values of ESDD are plotted against the conductivity, which is shown in Fig. 2. It is observed that the relationship between the conductivity and ESDD is linear. Some researchers arguments are different related to this relationship. According to one researcher the value of conductivity is equal to the square root of the ESDD value [7].

The correction conductivity and corresponding ESDD is measured for 0.1gm, 0.3gm, 0.5gm, 0.7gm and 0.9gm salt salinity using cm size glass plate. The correction conductivity and ESDD is plotted with those salt concentrations, which are shown in Fig. 3.

In Fig. 3, the variation of correction conductivity increases with increase in the salt concentration and this variation is almost linear. In the same Figure, the variation of ESDD is also linear with the amount of salt concentrations. The values of ESDD are plotted against with correction conductivity, which is shown in Fig. 4.

From Fig. 4, it is also observed that the relationship between the correction conductivity and Equivalent Salt Deposit Density is linear.

Conclusions

The values of correction conductivity and Equivalent Salt Deposit Density (ESDD) were measured for a glass plate with the variation of the amount of salt concentration. From the experiments, it is found that the variation of correction conductivity and ESDD are linear with the amount of salt concentrations. One researcher is mentioned the insulator surface conductivity is equal to the square root of the ESDD [7]. Based on the CIGRE [8], 1 mg/cm2 (ESDD) is equal to 100 (layer conductivity).

In the experiment, the relationship between the correction conductivity and ESDD has been examined and is found linear. In future, this relationship will be verified by more experiments.

References

[1] M. A. M. Piah, Ahmad Darus, “Modeling Leakage Current and Electric Field Behaviour of Wet Contaminated Insulators”, Power Engineering Letters, IEEE Transactions on Power Delivery, Vol. 19, N0. 1, pp. 432-433, January 2004.

[2] I. R. Vazquez, G. M. Tena and R. H. Corona, “Nonstandard Method for Accelerated Aging tests of Nonceramic Insulators, IEE Proc.-Gener. Transm. Distrib., Vol 149, No. 4, pp. 439-445, July 2002.

[3] M. Farzaneh, I. Fofana, C. Tavakoli, “Dynamic Modeling of DC Arc Discharge on Ice Surface”, IEEE Transactions on Dielectrics and Electrical Insulation, Vol. 10, No. 3, pp. 463-474, June 2003.

[4] J. P. Holtzhausen, W. L. Vosloo, “The Pollution Flashover of ac Energized Post Type Insulators”, IEEE Transactions on Dielectrics and Electrical Insulation, Vol. 8, No. 2, pp. 191-194, April 2001.

[5] F. V. Topalis, I. F. Gonos and I. A. Stathopulos, “Dielectric Behavior of Polluted Porcelain Insulators”, IEE Proc.-Gener. Transm. Distrib., Vol 148, No. 4, pp. 269-274, July 2001.

[6] International Electrotechnical Commission, “Artificial Pollution tests on High Voltage Insulators to be used on ac System”, IEC 60507-04, Switzerland, 1991.

[7] Ling An, Xiuchen Jiang, Zhendong Han, “Measurements of Equivalent Salt Deposit Density (ESDD) on a Suspension Insulator”, IEEE Transactions on Dielectrics and Electrical Insulation, Vol. 9, No. 4, pp. 562-568, August 2002.

[8] CIGRE working group 33.04, Study Committee 33, “A Critical Comparison of Artificial Pollution Test Methods for HV Insulators”, ELECTRA, No. 64, pp. 117-136, January 1979.