For design purposes, the specific knowledge about the creepage distance of the insulator for the contaminated environment is important. This can be done easily if the mathematical relationship between the creepage distance and Salt Deposit Density (SDD) is known. In this paper, a relationship between the creepage distance of the insulator and SDD has been proposed using the Dimensional Analysis technique. The results calculated from the proposed expression are compared with other results and found to be in close agreemen

Ahmad, Ahmad S.

Ahmad, Hussein

Buntat, Z.

Fuad, Syed Ahmad

Paul, K. C.

Piah, M. A. M.

Salam, Md. Abdus

Tamsir, T.

English

Universiti Teknologi Malaysia Institutional Repository

2000 Conference on Electrical Insulation and Dielectric Phenomena Study of Creepage Distance of the Contaminated Insulator in Correlation with Salt Deposit Density Md. Abdus Salam, Hussein Ahmad, Ahmad S. Ahmad, * Syed Ahmad Fuad, ** K. C. Paul, T. Tamsir, Z. Buntat, M. A. M. Piah Department of Electrical Power Engineering Faculty of Electrical Engineering Universiti Teknologi Malaysia * Tenaga Nasional Bhd Research Selangor, Malaysia ** Toronto University, Canada Abstract: For design purposes, the specific knowledge about the creepage distance of the insulator for the contaminated environment is important. This can be done easily if the mathematical relationship between the creepage distance and Salt Deposit Density (SDD) is known. In this paper, a relationship between the creepage distance of the insulator and SDD has been proposed using Dimensional Analysis technique. The results calculated from the proposed expression are compared with other researcher's results and found to be in close agreement. INTRODUCTION In the transmission lines operating 132 kV to 500 kV, the cap-and-pin glass insulators are used as either V- string or I-string configuration. They are usually served in-line with the cross arm to prevent the transverse movement of the conductor under all but extreme loads. At the same time horizontal VEE, horizontal line post and also strutlsuspension string have been used in the transmission network systems. The insulator leakage or creepage distance is dependent on its total height. The creepage distance of the insulator increased with increasing string length. The string length of the insulator is required to increase with increasing SDD value. The line insulators are exposed to the outdoor environment. These insulators are contaminated by the seawater spraying near sea and also by industrial fumes near the industrial areas. The insulation strength of those contaminated insulators is dependent on so many variables namely (1) the type and amount of contaminant and inert binder, (2) the configuration of the insulator, (3) the length of the insulator string, (4) weather conditions and testing method. The deposited contaminants on the insulator surface can be expressed and represented by the Salt Deposit Density. The creepage distance of the insulator is closely related with the SDD. Some researchers [ 1-31 have established the relationship between creepage distance and the SDD empirically. The data of the CIGRE working group [ 1 3  is given in terms of the withstand specific leakage or creepage distance in mmkV rms line to line voltage as a function of contamination level in terms of SDD. The IEEE working group [4] has proposed similar empirical relationship between creepage distance and SDD. For developing empirical relationship more working time and large amount of data is required. For minimizing these kinds of problems, a mathematical relationship between the creepage distance and the SDD of the contaminated insulator has been proposed using Dimensional Analysis technique. The proposed analytical expression has been verified by the other researcher's results. THEORETICAL DEVELOPMENT In the practical field, the creepage distance of the insulator directly depends on average diameter ( D ), Salt Deposit Density (SDD), exposure time ( e t )  and static arc constant ( N  ). According to Dimensional Analysis technique [ 5 ] ,  the relationship between them can be written as, p = F ( D ,  N ,  SDD,  et)  (1) where: F - Function; p - Creepage distance of the insulator; et - Exposure time of the insulator; N - Static arc constant; SDD - Salt Deposit Density. The dimensional matrix of the above variables can be written as, 0-7803-6413-9/00/$10.00 2000 IEEE 215 L M T A where: p D N SDD et -1 1 1 -2 0 -1 0 1 1 0 3 0 -3 0 1 1 0 n-1 0 0 L - Length in SI units; M - Mass in SI units; T - Time in SI units; A - Current in SI units; n , N - Arc constant. The rank of the above dimensional matrix is 4 and dimensionless product of the whole set is 1. The homogeneous linear algebraic equations from the above matrix can be written as follows, - k l + k ,  + k ,  -2k ,  = O  (2) - k l  + k, + k,  = O  3 k ,  - 3k3 + k, = O  k ,  + (n - 1) k, = 0 (3) (4) ( 5 )  Where k ,  , k 2  k,  k,and k ,  are the exponents of the respective variables. The expression of k, ,  k , ,  k,and k, intermsof  k,canbederivedfrom equation (2) to (5 ) .  These expressions are, 3n 1 n n - 1  n - 1  n - 1  k ,  =-kl , k 3  = --kl,k4 = k ,  9 - 3n n - 1  k,  =-k, By assigning the value of k ,  as 1 the expression of equation (6) can be written in matrix form as follows, kl k2 k3 k,  k ,  D N SDD et - - -  n-1 n-1 n-1 The general expression from the above matrix can be written as, By applying the Buckingham's, iz theorem [ 5 ] ,  equation (7) can be re-written as, - 3n I n 3 n  -- -  -p = d D n - l  N (SD13) "- '(et)  n - l  (8) Where dcis the dimensiona.1 constant. It should be noted that in an work [6] on application of Dimensional Analysis technique for relating insulators flashover voltage with pollution resistance, other variables were considered as constant. Therefore, in the present work equation (8) has been modified by denoting the exponent (?) byb and treating N and et as constants so as to highlight the relationship between creepage distance and Salt Deposit Density. ' n - 1  p=d , (SDD)bD3b  (9) COMPARISON OF RESULTS Actually the creepage distance of the insulator is the most important determinant for studying the contamination performance and also design purposes. The values of creepage distance are calculated from equation (9) with different values of d, , b for V-string and I-string insulator arrangement. For comparison, the calculated results are plotted with the other researcher's result [4] and are shown in Fig. 1. In Fig.1, it is observed that the creepage distance of the I-string insulator is much lower than the V-string insulator for the range of SDD value 0.04 to 0.1 mg/cm2. Because in case of V-string, large number of insulators are required than I-string. The results obtained from the proposed analytical expressions are more consistent with other researcher's results for both V and I string. Again the creepage distances for I-string are calculated from equation (9) for the ran,ge of SDD from 0.02 to 0.44 mg/cm2. These calculated values are plotted with the other researcher's results i. e. CIGRE [l], NGK [2], and CESI [3] results. These are shown in Fig. 2. From the Fig. 2, it has been seen that the proposed analytical results are in close agreem'ent with the NGK [2] researcher results. The deviatilon between the proposed analytical results and CIGRE [ l ]  results is slightly higher. Because in CIGRE [ I ]  models the values of 216 d, and b constants are considered 66 and 0.223 [I]  CIGRE Working Group 33.043 Study Committee, "A Critical Comparison of Artificial Pollution Test Methods for HV respectively. Insulators", ELECTRA, No. 64, pp. 117-136, January 1979. //- + IEEE I-string - - -X- - -Ana. I-string [2] I. Kimoto, K. Kito, and T. Takatori, "Anti- Pollution Design Criteria for Line and Station Insulators, IEEE Transactions on Power Apparatus and Systems, Vol. 91, pp. 317-327, 1972. [3] M. de Nogris, D. Perin and A. pigini, "Design of Extemal Insulation for AC Systems Under Polluted Conditions", CESI Technical Brochure, 1992. 1 0 0.02 0.04 0.06 0.08 0.1 0.12 [4] IEEE Working Group on Insulator Contamination, Lightning and Insulator Subcommittee, T & D Committee, Fig. 1. Variation of creepage "Application Guide for Insulators in a distance with SDD Contaminated Environment", IEEE Transactions on Power Apparatus and Systems, SDD [mg/sq.cm] Vol. 98, pp. 1676-1695, 1979. 2 40 - 5 3 0 -  cl 2 0 -  P) .- U 2 a E 1 0 -  V 0 - r  0 0.1 0.2 0.3 0.4 0.5 SDD [mg/sq.cm] Fig. 2. Specific creepage distances with SDD CONCLUSIONS Langhaar, H. L, "Dimensional Analysis and Theory of Models", John Wiley and Sons, Inc., New York, 195 1. Farouk A. M. Rizk, "Application of Dimensional Analysis to Flashover Characteristics of Polluted Insulators", IEE Proc,, Vol. 117, No. 12, pp. 2257-2260, 1970 The analytical expression between the creepage distance and Salt Deposit Density for the polluted insulator has been derived using Dimensional Analysis technique. The creepage distances calculated from the proposed analytical expression are compared with the other researcher's results and found to be in close agreement. REFERENCES 217 

Study Of Creepage Distance Of The Contaminated Insulator In Correlation With Salt Deposit Density

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Study Of Creepage Distance Of The Contaminated Insulator In Correlation With Salt Deposit Density

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