Sobre “B”: Documentación Técnica

The environmental considerations are getting more and more important under the presently changing climate. Therefore the survey asked whether the reported failures could have been influenced by environmental conditions exceeding the equipment service limits or not. All four different types of survey failure cards (CB, DS/ES, IT and GI) had the same categories so it was not necessary to re-code. Categories specified in the survey are listed in Table 5-94. Table 5-95 shows the collected number of major and minor failures in which the environment was presumed to have contributed to their development and in which it was not. The table shows absolute and relative data (100% is number of MaF, MiF respectively) and compares all data analysis with an analysis in which countries 14 and 23 data were disregarded.

Table 5-96 shows the same information from the GIS location point of view. It shows the collected number of major and minor failures in which the environment contributed to their development and in which it did not for two categories of all data, i.e. for indoor GIS and outdoor GIS.

Detailed analysis of individual stress contributions are shown in Table 5-94. The questionnaire allowed for multiple answers in this question and thus the total number of identified stresses is higher than the number of answers with a positive indication (100% is total number of ticks in MaF, MiF resp.). Figure 5-64 shows relative distribution of environmental stresses that contributed to GIS CB-bay major (MaF) and minor (MiF) failures (100% is the number of MaF, MiF respectively, in which the respondents identified environmental contribution).

Table 5-94: Distribution of environmental stresses that contributed to GIS CB-bay major (MaF) and minor (MiF) failures – all data (absolute and relative values based on total MaF and MiF that were influenced by the environment)

Kind of environment contribution (all data)

Number of

MaF %MaF

Number

of MiF %MiF

Temperature too low 1 1,3 5 3,3

Temperature too high 2 2,5 8 5,3

Strong wind 1 1,3 4 2,6

Rain 4 5,1 18 11,9

Sudden variation in

temperature 4 5,1 8 5,3

Snow, ice or hoar-frost 2 2,5 10 6,6

Corrosive atmosphere 3 3,8 0 0,0

Fog or high humidity 3 3,8 13 8,6

Pollution including dust 4 5,1 7 4,6

Lightning 21 26,6 49 32,5

Earthquake 0 0,0 1 0,7

Flood 28 35,4 0 0,0

Other 6 7,6 28 18,5

Total 79 100,0 151 100,0

Summary of the above (in summarized categories division):

Temperature 7 8,9 21 13,9

Water in the air 9 11,4 41 27,2

Atmosphere 7 8,9 7 4,6

Wind 1 1,3 4 2,6

Lightning 21 26,6 49 32,5

Flood and earthquake 28 35,4 1 0,7

94

Table 5-95: Distribution of GIS CB-bay major (MaF) and minor (MiF) failures that were not and were influenced by an environmental stress - all data and data without countries 14 and 23 (absolute and relative values based on total MaF and MiF)

Environmental contribution to the failure

All data Data without countries 14 and 23

Number of MaF Number of MiF Number of MaF Number of MiF Abs. % Abs. % Abs. % Abs. %

No contribution 285 79,6 1380 91,7 100 95,2 957 98,7

Contribution 73 20,4 125 8,3 5 4,8 13 1,3

Table 5-96: Distribution of outdoor and indoor GIS CB-bay major (MaF) and minor (MiF) failures that were not and were influenced by an environmental stress – all data (absolute and relative values based on total MaF and MiF)

Environmental contribution to the failure

Outdoor GIS (all data) Indoor GIS (all data)

Number of MaF Number of MiF Number of MaF Number of MiF Abs. % Abs. % Abs. % Abs. %

No contribution 189  73,8 608 87,7 96 94,1  772  95,1

Contribution 67  26,2 85 12,3 6 5,9  40  4,9

Figure 5-64: Relative distribution of environmental stresses that contributed to GIS CB-bay major (MaF) and minor (MiF) failures

Comparison with previous survey

In the 2nd _{GIS survey there were not any questions on environment stresses that would have}

presumed to contribute to failures. In the 2nd _{survey was a separate category called}

“operational conditions of a failure” (a part of “service conditions” characteristic in 3rd _survey)

and one of the options was “lightning overvoltage”. In the 2nd _{survey there were 6 MaF}

identified in this category. That is about 1,5% of MaF. This value is much lower than the same category in the 3rd survey (almost 27%).

Findings and commentary

Presumed environmental contribution to a failure was identified in 20% of MaF and 8% of MiF for all data and in 5% of MaF and 1% of MiF for data without countries 14 and 23. Having a look at the same question from the GIS location point of view, the outdoor GIS’s suffer more from the environment influence than indoor GIS. Presumed environmental contribution was identified in 26% of MaF and 12% of MiF that happened in outdoor GIS and only in 6% of MaF and 5% of MiF that happened in indoor GIS.

0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% MaF MiF Distribution of environmental contribution to a failure (all data) Other Flood and earthquake Lightning Wind  Atmosphere  Water Temperature 

95

As already written in chapter 5.6 there were 28 MaF in voltage class 1 caused by a flood. These failures represent 35% of all positively identified MaF influenced by nature. These failures were excluded from any other analysis than this one. The second most frequent environmental influence is lightning representing 27% of positively identified answers. As lightning overvoltage is concerned, in contrary to a flood, utilities can protect their equipment by installing surge arresters. However it is possible that the effect of lightning has been overestimated. It is much more difficult to estimate if the lightning has stressed the equipment in excess of its rating than if the temperature was out of the specified range.

Minor failures were more influenced by different kinds of humidity in the air and by air temperatures than major failures. Beside the lightning activity (32%) they represent 27% and 14% of positive answers. Keeping in mind that tightness and ageing problems were identified as the most frequent minor problems it is natural that humidity and air temperature can accelerate their development. The comment about possible overestimation of the effect of lightning applies also to the MiF.