1 Scope and purpose
This part of GB/T 26218 gives specific guidelines and principles to arrive at an informed judgment on the probable behavior of a given insulator in certain pollution environments.
This part is applicable to the selection of composite insulators for a.c. systems, and the determination of their relevant dimensions, to be used in high voltage systems with respect to pollution.
The contents of this part are based on CIGRE 33.13 TF 01 documents [1], [2], which form a useful complement to this part for those wishing to study in greater depth the performance of insulators under pollution.
This part does not deal with the effects of snow or ice on polluted insulators. Although this subject is dealt with by CIGRE [3], current knowledge is very limited and practice is too diverse.
The object of this part is to give the user means to:
——determine the reference unified specific creepage distance (USCD) from site pollution severity (SPS) class;
——choose appropriate profiles;
——apply correction factors for altitude, insulator shape, size and position, etc. to the RUSCD.
2 Normative references
The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.
GB/T 2900.8-2009 Electrotechnical terminology - Insulators (IEC 60050-471: 2007, IDT)
GB/T 24622-2009 Guidance on the measurement of wettability of insulator surfaces (IEC/TS 62073: 2003, IDT)
GB/T 26218.1-2010 Selection and dimensioning of high-voltage insulators intended for use in polluted conditions - Part 1: Definitions, information and general principles (IEC/TS 60815-1: 2008, MOD)
3 Terms, definitions and abbreviations
3.1 Terms and definitions
For the purposes of this document, the terms and definitions given in GB 2900.8-2009 and GB 26218.1-2010 and the following apply.
3.1.1
reference unified specific creepage distance; RUSCD
initial value of unified specific creepage distance for a pollution site before correction for size, profile, mounting position, etc. according to this part and generally expressed in mm/kV
3.2 Abbreviations
For the purposes of this document, the following abbreviations apply.
1 Scope and purpose
2 Normative references
3 Terms, definitions and abbreviations
3.1 Terms and definitions
3.2 Abbreviations
4 Principles
5 Materials
5.1 General information on common silicone rubber housing materials
5.2 Reduction of creepage distance
6 Determination of site pollution severity
7 Determination of the RUSCD
8 General recommendations for composite insulator profiles
9 Checking of profile parameters
9.1 General
9.2 Alternating sheds and shed overhang
9.3 Spacing versus shed overhang
9.4 Minimum distance between sheds
9.5 Creepage distance versus clearance
9.6 Shed angle
9.7 Creepage factor
10 Correction of RUSCD
10.1 Calculation
10.2 Correction for altitude Ka
10.3 Correction for insulator diameter Kad
11 Determination of the final minimum creepage distance
12 Confirmation by testing
Annex A (Informative) Technical deviations between this part and IEC 60815-3: 2008 and their justifications
Annex B (Informative) Information on pollution induced degradation of composite insulator
Bibliography
Figure 1 RUSCD as a function of SPS class
Figure 2 Typical “open” profiles
Figure 3 Typical alternating profile
Figure 4 Kad versus average diameter
Figure B.1 Operating areas as a function of pollution severity and USCD (for a fixed insulating length)
