GSU; 15/400 kV; 340 MVA; OFAF; sealed
Installed on Summer 2005, filled with naphtenic oil, new oil controlled (no problem found).
After 7 months: alert from Hydran sensor
Monitoring: firstly each week, later daily.
|
Gas
|
Date
|
16/07/05
|
29/07/05
|
09/02/06
|
Loading reduction
|
15/02/06
|
Electrical tests
|
16/02/06
|
17/02/06
|
|
Oxygen
|
ul/l
|
2651
|
5462
|
924
|
559
|
821
|
3055
|
||
|
Nitrogen
|
ul/l
|
8934
|
18462
|
8122
|
3963
|
5987
|
16142
|
||
|
Carbon dioxide
|
ul/l
|
78
|
96
|
298
|
155
|
206
|
309
|
||
|
Carbon monoxide
|
ul/l
|
11
|
11
|
79
|
35
|
50
|
84
|
||
|
Hydrogen
|
ul/l
|
0
|
0
|
1032
|
610
|
780
|
1092
|
||
|
Acetylene
|
ul/l
|
0
|
0
|
22
|
13
|
11
|
19
|
||
|
Methane
|
ul/l
|
0
|
0
|
2387
|
1369
|
1817
|
2634
|
||
|
Ethane
|
ul/l
|
0
|
0
|
657
|
352
|
475
|
701
|
||
|
Ethylene
|
ul/l
|
0
|
0
|
2322
|
1245
|
1680
|
2462
|
||
|
C3
|
ul/l
|
0
|
4
|
1697*
|
876
|
1153
|
1754
|
*Hydran alert
– The manufacturer supposed a overheating due to magnetic fields in the nucleus
– Diagnostic based on DGA: localized overheating, due to a bad clamping
Final results:During the internal inspection a bad clamping is found in the connection between one of the phases and the HV bushing, with confirmation of the localized overheating due to bad contant.
After repair and oil treatment a new monitoring planning is decided:
Conclusions:After fault Ethylene had an initial moderate increase, later stabilized at non dangerous values.
|
Fault found during the inspection
When DGA intercept the fault/case history |
