R. Suzuki

36-WG11 / Milan /93

October 2001

Draft Proposal of New Annex:

Pollution Deposit and Shed Profile of Insulators

Site severity should be determined by measurement data of ESDD and NSDD on reference insulators of 120-kN cap and pin insulator with normal shed profile or small diameter rod/post insulator with plain shed profile. In case site severity value is applied to insulators with different profile, careful attention should be paid to expected pollution degree of the relevant insulators. It seems difficult to determine definite correction factor for insulator profile on pollution degree because it may vary from a site to the other depending on pollution environments. But information about effect of insulator profile on pollution deposit might be useful for readers to deeply study the meaning of site severity. So it would be proposed to provide such information in Annex. Draft Annex is shown as follows, where the data given in document 36-WG11/Warsaw/24 and IEEE Paper 89 SM 770-9 PWRD (authored by F. Zedan and M. Akbar in 1989) are used as typical examples. ----------------------------------Annex G (informative): Pollution Deposit and Insulator Profile Pollution deposit characteristics depend on insulator profile. In addition such dependence is influenced by pollution environments. In this regard, there are some information given below for reference. It should be noted that all the data shown hereafter are just typical examples obtained in certain environments and other data may be observed in different environments at site. In rapid pollution environments, pollutant deposits on the insulator surface for a very short time under strong wind condition. In this case washing by rain or heavy fog can not usually be expected during the occasion and deep under-rib type profile, e.g., anti-fog disc shed, can protect the bottom surface of the insulator from pollutant deposit, resulting in reduced pollution degree. Table G1

1

shows typical example of ESDD measurements on various insulators in coastal regions. Pollution deposit characteristics of post and hollow insulators is influenced by their diameter in rapid pollution environments. The larger the diameter becomes, the less ESDD can be expected. Typical example of measurement data is shown in Fig. G1. Table G1 Comparison of measured ESDD among various insulators in rapid pollution environments Insulator type and profile (diam., spacing, creepage dist., mm)

Cap and pin, standard shed (Ф254, 146, 280)

Cap and pin, standard shed (Ф280, 170, 370)

Cap and pin, anti-fog shed (Ф254, 146, 432)

Cap and pin, anti-fog shed (Ф320, 170, 550)

Long-rod, under-ribbed shed (average diam.Ф127)

Comparison of ESDD 1.01) 0.761) 0.641) 0.601) 1.44

Note: 1) ESDD on bottom surface of cap and pin insulators.

Fig. G1 Effect of average diameter on ESDD in rapid pollution environments In ordinary pollution environments, where pollutants gradually deposit on the insulator surface and rain occasionally washes the insulator surface, pollution

2

deposit characteristics of different insulators depend on pollution type, pollution sources, meteorological conditions, etc. Typical example of measured ESDD ratio is shown in Tables G2 and G3, where the ESDD near coasts and in deserts is compared among insulators with different profile, respectively. Table G2 Comparison of measured ESDD among various insulators in ordinary pollution environments near coasts Insulator type and profile (diam., spacing, creepage dist., mm)

Comparison of ESDD

Cap and pin, standard shed

1.01)

(Ф254, 146, 280)

Cap and pin, standard shed

0.791)

(Ф280, 170, 370)

Cap and pin, anti-fog shed

0.69-0.921)

(Ф254, 146, 432)

Cap and pin, anti-fog shed

0.611)

(Ф320, 170, 550)

Long-rod, normal shed (average diam.Ф115) Long-rod, under-ribbed shed (average diam.Ф127)

0.29-0.39 0.48

Note: 1) ESDD on bottom surface of cap and pin insulators.

Table G3 Comparison of measured ESDD among various insulators in ordinary pollution environments in deserts Insulator type and profile (diam., spacing, creepage dist., mm)

Comparison of ESDD

Cap and pin, standard shed Cap and pin, anti-fog shed Cap and pin, aerodynamic shed Long-rod, aerodynamic shed

------------------------------

3

1.0 0.90 0.31-0.34 0.21