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Appendix
current curve in real time. For this measurement, the transient recording
functionality of the OMICRON CMC 256 was used (see Figure 5-13 "Dynamic
resistance measurement for analysis of the diverter switch").
5.1.9 Turns Ratio
This test is normally only performed if a problem is suspected from the DGA,
dissipation factor test or relay operation. The turns-ratio test detects shorted
turns, which indicate insulation failure. Shorted turns may result from short
circuits with high currents or insulation failures. The voltage ratio obtained by the
test is compared to the boilerplate voltage ratio. The ratio obtained from the field
test should agree with the factory value to within 0.5%. New transformers
normally compare to the boilerplate within 0.1%. With the described test system,
it is additionally possible to measure the ratio with magnitude and phase angle
over a wide frequency range.
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General