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Analysis of power transformers failures According to statistics about 85% of all breakdowns of power transformers are attributed to the failure of the insulating system. So how big are losses related to insulation failure? For the period from 1997 through 2001 a research was conducted by The Hartford Steam Boiler Inspection & Insurance Co. with a purpose to analyse reasons of breakdowns of power transformers rated at 25 MVA and above. Results were presented at International Association of Engineering Insurers, 36th Annual Conference – Stockholm, 2003. |
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Table 1 displays losses caused by property damage and business interruption. |
Year |
Total number of breakdowns |
Total Loss |
Total Property Damage |
Total Business Interruption |
|
1997 |
19 |
$ 40,779,507 |
$ 25,036,673 |
$ 15,742,834 |
|
|
1998 |
25 |
$ 24,932,235 |
$ 24,897,114 |
$ 35,121 |
|
|
1999 |
15 |
$ 37,391,591 |
$ 36,994,202 |
$ 397,389 |
|
|
2000* |
20 |
$ 150,181,779 |
$ 56,858,084 |
$ 93,323,695 |
|
|
2001 |
15 |
$ 33,343,700 |
$ 19,453,016 |
$ 13,890,684 |
|
|
Total |
94 |
$ 286,628,811 |
$ 163,239,089 |
$ 123,389,722 |
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Table 2 displays costs of breakdowns per MVA. Calculation takes into consideration only 78 failures in total, because for the rest of them transformers size was unknown. During this five year period, the average cost was $8,990 per MVA. |
Year |
Total number of breakdowns |
Breakdowns of transformer with known size |
Total MVA reported |
Total PD (with site data) |
Cost per MVA |
|
1997 |
19 |
9 |
2567 |
$20,456,741 |
$7,969 |
|
|
1998 |
25 |
25 |
5685 |
$24,897,114 |
$4,379 |
|
|
1999 |
15 |
13 |
2433 |
$36,415,806 |
$14,967 |
|
|
2000 |
10 |
19 |
4386 |
$56,354,689 |
$12,849 |
|
|
2001 |
15 |
12 |
2128 |
$16,487,058 |
$7,748 |
|
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Total |
94 |
78 |
17,199 |
$15,4611,408 |
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Table 3 lists the costs and number of failures for each cause of failure. |
Cause of Failure |
Number |
Share of Failure |
Total Paid |
Share of the Cost |
|
Insulation Failure |
24 |
25.53 % |
$ 149,967,277 |
52.32 % |
|
|
Design /Material/Workmanship |
22 |
23.4 % |
$ 64,696,051 |
22.57 % |
|
|
Unknown |
15 |
15.96 % |
$ 29,776,245 |
10.39 % |
|
|
Oil Contamination |
4 |
4.26 % |
$ 11,836,367 |
4.13 % |
|
|
Overloading |
5 |
5.32 % |
$ 8,568,768 |
2.99 % |
|
|
Fire /Explosion |
3 |
3,19 % |
$ 8,045,771 |
2.81 % |
|
|
Line Surge |
4 |
4.26 % |
$ 4,959,691 |
1.73 % |
|
|
Improper Maint /Operation |
5 |
5.32 % |
$ 3,518,783 |
1.23 % |
|
|
Flood |
2 |
2.13 % |
$ 2,240,198 |
0.78 % |
|
|
Loose Connection |
6 |
6.38 % |
$ 2,186,725 |
0.76 % |
|
|
Lightning |
3 |
3.19 % |
$ 657,935 |
0.23 % |
|
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Moisture |
1 |
1.06 % |
$ 175,000 |
0.06 % |
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Total |
94 |
|
$ 286,628,811 |
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Conclusion Insulation failures were the leading cause of failure in this study. This category excludes those failures where there was evidence of a lightning or a line surge. There are actually four factors that are responsible for insulation deterioration: pyrolosis (heat), oxidation, acidity, and moisture. But moisture is reported separately. The average age of the transformers that failed due to insulation was 18 years. |
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