179
Appendix
Figure 12-37 DF of an OIP 154 kV bushing (1970)
These results show that the frequency scan method will enable more detailed
insulation analysis in the future. But it is necessary to compare the curves to
fingerprint measurements. This way it will be possible to detect changes in
insulation at a very early stage.
12.9.17 Summary
With advancing age of transformers, a regular check of the operating condition
becomes more and more important. The analysis of the gas in oil is well-proven
method of analysis but must be complemented by efforts to locate any faults
indicated by excess hydrocarbon gases in the oil. This way important
maintenance can be performed in time to avoid a sudden total failure. The fault
location can be successfully performed using simple electrical methods, such as
resistance measurements.
The described new test technology enables DF frequency scans which, by
comparing DF curves to fingerprints it will be possible to detect degradation in
insulation at a very early stage with a more detailed analysis. Additionally,
excellent suppression of electromagnetic interference is guaranteed.
With the described system, other interesting tests can be performed such as
zero sequence measurements without additional equipment; current
transformers can be tested up to 2000A (ratio, polarity, excitation curve,
burden …); voltage transformers can be tested up to 2000V, contact
resistances, ground and line impedances can be measured and a lot of
additional applications are possible.
All measurements can be performed quickly and efficiently with automatic test
procedures enabling simple operation such that all results are saved in one
system. Essentially, the whole test report and diagnosis can be created
automatically.
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