
3. Setting Up and Running a Test
72A-2570-01 Rev. K 07/2011
3-29
Repeat Results for One Phase at Different Times
The two responses in
were taken 18 months apart. The original
data was taken as a baseline set of results; the subsequent data was taken after
an incident involving the transformer. The results are similar.
Figure 3.45 Repeat Results for One Phase
Low-frequency variation, below about 5 kHz, is characteristic of core
magnetism affecting the results. The traces have the same basic shape, but one
is offset compared to the other. They come back into line as they approach
10 kHz.
The higher-frequency results are almost identical. This is strong evidence that
there has been no change in this transformer.
Results Showing a Shorted Turn
A shorted turn produces an effect similar to shorting the low-side windings for
a short-circuit measurement. The effect is easy to see at low frequencies and
does not require reference results.
The original results show the characteristic low-frequency response of a wye
(star) winding. The subsequent results, taken a year later after a close-in fault,
show the characteristic response of a short somewhere on that phase.
Содержание SFRA
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