IEC 60815-1 pdf download Selection and dimensioning of high-voltage insulators intended for use in polluted conditions — Part 1: Definitions, information and general principles
Table 1 shows the data and decisions needed within each approach.The applicability of eachapproach depends on available data, time and economics involved in the project.The degreeof confidence that the correct type and size of insulator has been selected varies alsoaccording to the decisions taken during the process. lt is intended that if “shortcuts” havebeen taken in the selection process，then the resulting solution will represent over-designrather than one with a high failure risk in service.
ln reality，the pollution performance of the insulator is determined by complicated anddynamic interactions between the environment and the insulator. Annex B gives a briefsummary of the pollution flashover mechanism.
In Approach 1, such interactions are well represented on an operating line,or substation, andcan also be represented in a test station.
In Approach 2, these interactions cannot be fully represented by laboratory tests， e.g. thetests specified in lEC 60507 and lEC/TR 61245.
ln Approach 3, such interactions can only be represented and catered for to a limited degreeby the correction factors. Approach 3 can be rapid and economical for the selection anddimensioning process but may lead to under-estimation of the SPS or to a less economicalsolution due to over-design.The overall costs，including imposed performance requirements,have to be considered when choosing from the three approaches.Whenever circumstancespermit,Approaches 1 or 2 should be adopted.
The time-scales involved in the three approaches are as follows:
For service experience (Approach 1), a period of satisfactory operation of five to ten years can be considered as acceptable. This period may be longer or shorter according to thefrequency and severity of climatic and pollution events.
For test station experience (Approach 1), a period of investigation of two to five years canbe considered as typical. This period may be longer or shorter according to the testprotocol and severity.
For measurement of site severity (Approaches 2 and 3), a period of at least one year isnecessary (see 8.2).
For estimation of site severity (Approaches 2 and 3), it is necessary to carry out researchinto the climate and the environment and to identify and analyse all possible pollutionsources. Hence，estimation is not necessarily an immediate process and may requireseveral weeks or months.
For laboratory testing (Approach 2), the necessary time is a matter of weeks or monthsdepending on the type and scale of tests.
The following clauses give more information on system requirements, environment and site pollution severity determination.
An example of a questionnaire that can be used in Approach 1 to obtain operational experience from an existing line or substation is given in Annex H.