Alternating long and short sheds are beneficial in areas where heavy wetting can ... An alternating housing profile can be designed in general with all kinds of ...
36-WG11/Capetown/141 36(Bejing/Germany)04 Comments on 36/191/CD: IEC 60815-2 Ed.1 “Selection and dimensioning of high voltage insulators for polluted conditions. - Part 2: Ceramic and Glass insulators for a.c. voltage“ The comments also apply to 36/187/CD
With reference to the comments submitted earlier and contained in the relevant compilation of comments details are given below.
Chapter 9.1 should read (has also to be changed in IEC60815-1): 9.1 General recommendation for profiles (repeated from IEC60815-1) Aerodynamic or open profiles prove to be beneficial in areas where the pollution is deposited onto the insulator by wind, such as deserts, heavily polluted industrial areas or coastal areas which are not directly exposed to salt spray. This type of profile is especially effective in areas that are characterised by extended dry periods. Open profiles are also accessible for easy cleaning under maintenance. Standard profiles are effective for use in “very light“ or “medium“ polluted areas where a long creepage distance or aerodynamical effective profile is not required. The use of fog-type (anti fog) profiles with steeper shed inclination or with under-ribs, are beneficial in areas exposed to a salt water fog or spray, or to other pollutants in the dissolved state. These profiles may also be effective in areas with a particulate pollution precipitation containing slow dissolving salts. Alternating long and short sheds are beneficial in areas where heavy wetting can occur. An alternating housing profile can be designed in general with all kinds of shed profiles. See figure 2 for definition of the described housing profile types:
1
Figure 2 on page 17 should be as follows:
Figure 2 – Typical ceramic post, long rod and hollow insulator shed profile a) Aerodynamic or open profile (plain shed) b) Standard profile (uniform plain shed, inclination approx. 18°). Sheds of standard profile may also be equipped with a “small nose“ at the rim (“drop edge”). c1) Fog-type profile with plain sheds of steeper shed inclination c2) Fog-type profile with under-ribs d) Alternating sheds Alternating sheds can be designed of any shed profile type a) b) and c) 2
Replace table 3 and table 4 only by one table, i.e. new table 3 as follows. Table 3:
The selection of profile for vertical and horizontal a.c. long rod, post and hollow insulators
Polluted Areas Desert
Open Profile
Standard Profile
Fog-type Profile
Areas with sandy soils or in a desert location. These areas can be extensive polluted. Pollution that dissolves slowly has a high inert component, mainly wind borne.
Collects less pollution, as other profiles
More wind borne deposit accumulates on the underside of the sheds, in particular sheds with under-ribs have reduced natural cleaning by wind.
Gives good self-cleaning by wind.
Coastal Areas in direct vicinity of the coast, but in some cases can be as far inland as 10-20 km inland. Rapid pollution build-up and effective washing (not very adhesive).
Total surface becomes polluted but is accessible for natural cleaning.
Total surface becomes polluted but is accessible for natural cleaning.
Steeper shed inclination or under-ribs prevent wetting of the whole underside during rain.
Needs relatively long string length. More wind borne deposit accumulates on the underribs. Moderate natural cleaning.
Quick dissolving pollution. Has low inert component.
Long creepage distance per string length.
Pollution by wind and gravity.
Industrial/Agriculture Areas in close proximity to the industrial pollution source, may only affect a few installations. Conductive particulate pollution. (Cement, coal, chemicals, NOx, SOx etc.
Reduced pollution deposit. Easier to clean
Total surface becomes polluted but is accessible for natural cleaning.
Ribs collect pollution and do not self-clean.
Pollution that dissolves slowly has medium or high inert component, often heavy particles which settle on horizontal surfaces.
Inland (Low Pollution) No advantages provided by the open profile.
The added creepage distance is unnecessary.
All types of profiles can be designed with alternating shed projections. Alternating shed profiles may have advantages under heavy wetting conditions. Alternating shed profiles can be designed for the specific pollution area with all 3 profile types (“open“, “standard“, “fog-type“) to consider also heavy rain conditions. The pollution deposit on hollow and post insulators reduces with increasing diameter. However, the pollution flashover voltage reduces with increasing diameter. Recommended
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